Bolanical Journal of the Linnean Socie!v (l982), 84: 223-256. With 93 figures
Fragmentary non-vascular plant
microfossils from the late Silurian of
Wales
DIANNE EDWARDS, F.L.S.
Department of Plant Science, University College,
P.O. Box 78, Cardiff CFI IXL, Wales
Received j i b 1981, accepted for publication Scptnnbn, I981
A wide variety of cuticles and tubular elements is described from a late Silurian (Ludlow Series)
locality in Wales which has already yielded a macroflora containing Cooksonia Lang, Slcgonothcca
Edwards and vascularized axes. These microfossils are compared with Lang's Downtonian
.V'matofhallus complex and Silurian assemblages of similar composition from north America. It is
concluded that the majority of these microfossils derive from non-vascular plants of uncertain affinity
which lived on land.
KEY WORDS:--cuticles
late Silurian
Prohtaxites - tubular elements.
~
-
Nemaloplexw
~
.Nemotothallus
~
non-vascular land plants
CONTENTS
Introduction . . . . . . . . . . . .
Locality, material and methods.
. . . . . . .
Description of cuticle remains . . . . . . . .
Categories ofcuticle . . . . . . . . .
SEMs ofcuticles . . . . . . . . . .
Description of tubular elements.
. . . . . . .
Comparison with similar microfwsils from Silurian sediments.
Taxonomic status of the microfossils. . . . . . .
Affinities and nature of .rVemafathallw
. . . . . .
. . . . .
Affinities and nature of tubular elements
Conclusions . . . . . . . . . . . .
Acknowledgements. . . . . . . . . . .
References.
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INTRODUCTION
I first visited Capel Horeb Quarry, Powys in 1965 in search of Cooksonia
downtonensis. Heard (1939) had collected and described this fossil from the
Downtonian Long Quarry Beds at Capel Horeb, but his figured material has since
disappeared. The fertile specimens which I found in the same beds were
subsequently described as Steganotheca striata (Edwards, 1970) as they did not
conform exactly to Heard's specific diagnosis for C. downtonensis, although I am
+
0024 4074/82/030223 34$03.00/0
223
01982 The Linnean Society of London
224
D. EDWARDS
convinced from his illustrations that they are synonymous. In the same paper I
mentioned the abundance of plant remains in the older Roman Camp Beds
(Whitcliffe Formation : Ludlow Series). These have since been more intensively
studied as part of a research project on the early history of vascular plants in Wales
and the Welsh Borderland. In addition to Hostinella and small fragments of
unbranched smooth axes (Edwards & Davies, 1976), sporangia of Cooksonia and
Steganotheca (Edwards & Rogerson, 1979) have been recorded. During the search
for unmistakably vascular plants, which involved bulk maceration and film pull
techniques, a large number of microfossils has been recovered. These include
spores, spore masses, tubes and cuticles, many assignable to the Nematothallus
complex (Lang, 1937). In particular, the cuticles indicate that the parent plants
were adapted to the terrestrial environment, a conclusion reached by Lang (1937)
following an investigation of slightly younger Downtonian remains. Like Lang, I
have had little success in elucidating the morphology, anatomy, reproductive
structures (and hence affinities) of these plants and have been reluctant to publish
incomplete, fragmentary data from Capel Horeb and other Silurian localities. It is
unfortunate that this attitude has allowed the criticism that I have failed to
appreciate the relevance of such microfossils to issues such as the colonization of the
land and the origin of vascular plants and that I have overconcentrated on
recording the stratigraphic history of vascular plants (Edwards, Bassett &
Rogerson, 1979; Gray & Boucot, 1980). Here I hope to redress the balance,
although I must emphasize that, in my opinion, the microfossils in this late Silurian
locality have little to do with the ancestry and origin of vascular plants. They are
relevant to the early colonization of the land only in their similarities with the
much older fragments of land plants described by Pratt, Phillips & Dennison
(1978) and Strother & Traverse (1979). The importance of these fragmentary
remains lies in their numbers and diversity, which have permitted a rigorous,
detailed study.
LOCALITY, MATERIAL AND METHODS
Capel Horeb Quarry is situated on the north side of the AM, 9 km east of
Llandovery. An account of its geology is given in Friend & Williams (1978). The
plant remains described here come from the Upper Roman Camp Beds just below
the unconformity (( 1) in Friend & Williams, 1978: fig. 41) and occur both on the
main quarry face and the scree below. The fauna has been described by Potter &
Price (1965), who consider the Upper Roman Camp Beds to be upper Ludfordian
(uppermost Ludlow Series) (Holland, Lawson, Walmsley & White, 1980). The
results of a preliminary palynological study are recorded in Richardson & Lister
(1969).
Coalified compression fossils are present throughout the upper layers of greyblue shaley siltstone. Some bedding planes are covered with small, irregular
patches of coalified material together with occasional unbranched or forking axes,
the latter assignable to Hostinella (Fig. 1). Fertile specimens are rare. Wider axes
with surface striations and less regular appearance are tentatively assigned to
Prototaxites. Occasionally, more extensive coalified encrustations with a polygonal
surface patterning and large conspicuous perforations are found. Such fossils were
originally described as plants (Thallomia; Heard & Jones, 1931) but are now
believed to be of arthropod origin (Dictyocaris; Rolfe, 1969).The plants are usually
NON-VASCULAR MICROFOSSILS FROM WALES
225
preserved as coalified compressions with some persistant cuticle. Occasional rusty
stains on rock surfaces, sometimes associated with the compressions, led to a search
for iron sulphide petrifactions, but to date only one pyritized axis of tubular
construction has been found.
In bulk maceration, small pieces of rock were dissolved in commercial strength
hydrofluoric acid. Larger fragments of coalified material thus liberated were
decanted and repeatedly rinsed. These specimens were either oxidized (cleared) in
Schulze’s solution for several hours, washed and mounted in Canada Balsam, or
prepared for scanning electron micrography by being cleaned in hydrochloric
acid, dried in a desiccator and mounted on double-sided Sellotape on a stub.
Smaller fragments were strewn on to DAG silver paint on a coverslip and air dried.
The coverslip was then stuck to a stub. Some of the larger oxidized pieces of cuticle
and wefts of tubes were embedded in methacrylate resin and sectioned using a
rotary microtome with glass knife.
All the specimens from which film pulls were prepared were first photographed.
They were then covered with several coats of cellulose nitrate in amyl acetate. The
resulting cellulose nitrate films were removed from the rock and mounted. I n the
majority of cases, they needed no further oxidation. The fragmentary plant
remains thus isolated fell into three major groups: spores, tubes and cuticles.
DESCRIPTION OF CUTICLE REMAINS
Bulk maceration yielded small fragments of cuticle displaying a reticulate
patterning similar to that which Lang described for .Vematothallus (Lang, 1937).
Far larger pieces were recovered on the film pulls taken from the irregularly
shaped patches of coalified material which crowded certain bedding planes (Fig.
1 ) . SEM studies on unoxidized macerated fragments (Figs 35-41) show that the
general organization of these cuticles parallels that in vascular plants (Stace, 1965)
where one surface (the outer) is normally smooth and the other (the inner) is
protracted into a reticulum of flanges which mark the position of the anticlinal
epidermal cell walls. Being uncertain of the nature of the underlying tissue in the
fossil plants, I propose to call the areas between the flanges, ‘units’. The vast
majority of fragments isolated were of this kind viz. cuticles rather than sheets of
thick-walled cells (Schopf, 1978; Pratt et a/., 1978). A preliminary examination of
the numerous film pull preparations revealed considerable diversity in the shape
and size of the units. Indeed where more extensive areas were recovered it was
possible to see variation within a single fragment. Here I propose to categorize the
variants to facilitate identification. It proved impossible to prepare film pull
specimens for SEM work as the cuticles disintegrated when the cellulose acetate
film was dissolved. In more recent studies from other localities it has been possible
to make permanent mounts and SEM preparations of both surfaces from a single
piece of cuticle isolated by bulk maceration. Here the pieces were too small and it
has been a major problem to relate light and SEM observations.
Cuticle thickness : Differences in cuticle thickness are particularly well demonstrated
in SEM preparations (Figs 35-39). In Fig. 39 the cuticle is so thin that the
positions of the flanges are visible as lighter lines on the outerside and in some areas
the cuticle has collapsed inwards over the centre of the unit. Most specimens are
much thicker (Fig. 36). In mounted macerated and film pull cuticles, thickness
15
226
D.EDWARDS
may be difficult to estimate because of variation in colour. That thicker cuticles are
darker is obvious from the‘dark brown lines which mark the positions of the
flanges, while in certain kinds of macerated cuticle there are occasional lighter
units (Fig. 21) where the cuticle itself is thinner. O n film pulls difficulties arise in
interpreting the thickness of cuticles which range from a pale straw colour with
prominant dark flanges (Fig. 6) to almost black where flanges are difficult to
delimit (Fig. 13). In some cases these differences may reflect the extent of natural
oxidation (weathering) in that darker cuticles may be more heavily coalified.
However, where cuticles of different colours lie alongside each other on the same
film pull, it is possible that the variation reflects differences in thickness.
Thickness and depth of Jranges: Being tapering structures, flanges are difficult to
quantify and are best examined by SEM. Changes in thickness may also be
observed by slowly focusing through the cuticle in mounted macerated examples,
but such changes are less obvious on film pulls, which show the most variability. In
some cases, the flanges are well-defined and enclose angular units (Fig. 6 ) ; in
others they are more difficult to delimit, gradually merging into the cuticle above
the unit, which then has a more rounded appearance (Fig. 11). Such variation
may indicate differences in the topography of the outermost ‘cellular’ layer of the
plant. It is also seen in some SEMs (cf. Figs 36, 37) although it is possible, but
considered unlikely, that the flatter kind with ridge-like flanges (Fig. 36) may be
more compressed. Thickness of flanges on any one piece of cuticle (taken at any
one level of focusing) is rarely uniform, indeed in a few cases pronounced
thickenings may limit circular or oval units. Finally, more extensively thickened
areas, (each marking the junction of several units) are here termed blank units
(e.g. Fig. 13). The thickened area may be either symmetrical normally extending
into four flanges, or irregular (Figs 36, 41).
Shape and size of units: Perhaps the most striking feature of these cuticles is the
variation in size and shape of the units, resulting in a lack of any regular pattern or
alignment over a wide area. The units are usually polygonal in outline, rarely
circular or oval. When polygonal they may be regular or irregular, the latter
predominating, and vary in number of sides. Their appearance is closely related to
the kind of flange present.
I began this analysis by photographing all the better-preserved cuticles at the
same magnification and from contact prints of these films divided the specimens
with more or less regular reticulum into three groups on the basis of unit size.
Subsequent detailed measurements showed that mean diameter of units in the
small class is < 9.0 pm, in the medium class, 10.0-16.0 pm, and in the larger class
> 17.0 pm. Within each group there are some cuticles which exhibit a wide range
of unit diameter and some a narrow range. Where the range is wide almost all the
measurements may fall close to the mean, although in other cuticles there is a
greater spread of measurements. Occasional smaller or larger units may be
scattered over the cuticle or clustered. In some cases a large unit is surrounded by
numerous smaller ones so that it has a more rounded appearance.
Perforations: All the cuticles are astomatous; most imperforate. O n some film pulls
there are holes coincident with circular or oval units. In many cases careful
examination shows a narrow jagged rim of cuticle around the holes suggesting that
they are produced by the wearing away of the inner areas of the cuticle. Only in a
few specimens am I convinced that the cuticles are naturally perforate, the holes
again occupying a single unit. Perforate forms recovered on bulk maceration have
NON-VASCULAR MICROFOSSILS FROM WALES
227
been examined by SEM but none of these can be related to the six major categories
circumscribed below and will be included as anomalous forms.
Categories of cuticle
Category I :Reticulum with regular appearance, comprising more or less sodiametric, angular
units (Figs 2-9) : The fragments of a small piece of macerated cuticle illustrated in
Fig. 2 are typical of the medium size range (5.G13.6 pm) in which most of the
measurements lie close to the mean. Very small flanges are more or less uniformly
wide ( 1.5-2.0 pm). A second macerated example (Fig. 3) has a slightly greater size
range (5.0-16.2 pm) with the smaller units more clustered together. Most of the
units are isodiametric, but may appear more rounded where surrounded by
numerous others. Some are less regular, a few being elongate with parallel sides.
This specimen (Fig. 3 ) illustrates blank units particularly well so that in some areas
the reticulum resembles the wall system found in transverse sections through
angular collenchyma.
A typical film pull preparation showing a similar range in unit diameter is
illustrated in Fig. 5. It is a much more extensive piece ofcuticle than the macerates
and combines their characteristics in that, although most of the units are
isodiametric, some are less regular and there are occasional larger, more rounded
ones. Flanges are prominent and of more or less uniform width (1.5 pm)
throughout. Although this specimen (Fig. 4) has quite a distinctive sinuous shape, it
is unlikely that it is the shape of a complete organism because the edges are jagged,
with incomplete marginal units. Specimen ,VMW 7734G 27u, although possessing a
similar range in unit diameter (4.5-20.0 pm) and flange thickness ( 1.5 pm), has a
completely different, far more angular appearance, because the units have
consistently fewer sides, rarely as many as six. An extensive area of cuticle is again
preserved and it shows variation in patterning, with small units of few sides and
uniform diameter in some regions and the smaller units intercalated among larger,
angular ones in others (Fig. 6).
The smallest reticulum recovered from bulk maceration is illustrated in Fig. 7. It
has a uniform appearance because most of the units fall within a narrow size range
(2.0-3.0 pm; flange thickness, 1.0 pm).
At the other end of the size range are the two film pulls shown in Figs 8, 9.
Specimen NMW 77 34G 28a (Fig. 8) looks very similar to a cuticle already
described (Fig. 5 ) but its mean unit diameter is greater (8.0-18.0pm; mean
15.0 pm). The remaining specimen (Fig. 9) comprises a much lighter (?thinner)
cuticle with well-defined flanges and is sporadically preserved over a wide area
(12 mmz). In some places the patterning is obscured by dark coalified material
lacking any organization. The part illustrated in Fig. 9 shows a regular reticulum
comprising isodiametric units of similar diameter. In other regions there are
occasional isolated smaller units (range 5.0-18.0 pm; mean 15.0 pm; flange
thickness 1.O pm) .
Category 2: Reticulum with regular appearance composed of more or less isodiametric rounded
units (Figs 20-24) : Cuticles in this category are often dark with flanges difficult to
delimit accurately. While Category 1 cuticles are evenly coloured except at the
flanges and are interpreted as being of uniform thickness, some of the units in this
category, particularly the larger ones, are lighter perhaps indicating thinner
cuticle. However, as this group is known only from film pulls, it is possible that
228
D. EDWARDS
NON-VASCULAR MICROFOSSILS FROM WALES
229
such wider expanses are more easily torn on film pulls or are differentially oxidized.
It is also likely that cuticles in this category correspond to the SEMs (e.g. Fig. 39)
which show deeply concave units enclosed by well-developed, tapering flanges.
The cuticles illustrated in Figs 11 & 12 are superficially similar with units having
approximately the same size range (5.0-1 7.5 pm) but they may be distinguished
on small differences in unit shape and in the distribution of unit diameter
measurements. Specimen NMW 77 34G 27b (Fig. 1 1) most closely approximates to
the cuticles already described in that over 80°;, of the units are isodiametric and
regular in shape with a large number of unit diameter measurements close to the
mean (10.0 pm). Flange width is 3-4 pm. The units in specimen NMW 7734G 266
(Fig. 12) are less regular, ranging from almost circular to elongate with nearly a
third not isodiametric. Indeed perhaps some areas in this particular cuticle would
be more suitably placed in a separate category. Both the mean diameter (8.0 pm)
and variance about the mean are lower. Flange thickness is also less uniform
(2-4 pm) with occasional straight, narrow flanges.
Many of the cuticles in this category have a mean unit diameter of < 10 pm.
Two examples are shown in Figs 13 & 14, which demonstrate the difficulties of
measurement ; they are very dark, but, where small areas of reticulum are visible,
they correspond to the regular (Fig. 13) or irregular forms (Fig. 14) just described
although the unit diameter range is much smaller with unit diameter rarely
> 12.5 pm. Flanges thickness is 3-4 pm and there are fewer lighter units.
Small irregular cracks are not uncommon throughout the film pull preparations
and are presumably the reasons for the absence of larger pieces of cuticle in
macerates. Typical of many of the cuticles in this particular category is the pattern
of shrinkage cracking (shown in Fig. 10) which usually occurs towards the edge of
the specimen where the reticulum is completely obscured. Such a pattern is
perhaps produced by the drying of a thick cuticle. It seems more likely that it
occurred during diagenesis rather than before burial, although there is also the
possibility that some cracking resulted from alternate wetting and drying of
cuticular fragments on exposed rock surfaces in the quarry.
Category 3: Reticulum wilh irregular appearance comprising angular units of varying shape
and size (Figs 2 . 5 2 7 ) : These cuticles have a far more variable appearance (Figs
15- 17). Specimen NMW 77 34G 27c is an excellent example of a film pull in which
the units are almost all angular and, although more or less isodiametric, are less
regular than those previously described. There is a wide range in unit diameter
(5.0-25.0 pm; mean 10.0 pm) and apart from a very small number which exceed
20 pm there are approximately equal numbers of each width. Flanges are straight
and uniformly wide (2.0 pm).
I have not seen an exact counterpart in the macerated specimens, although the
fragments illustrated in Fig. 16 have a far less regular appearance than those I have
already described (Figs 2, 3, 7). The units are variable in shape with occasional
Figures 1 10. Fig. 1. Typical rock surface from the Roman Camp Beds (Whitcliffe Formation: Ludlow
Series) from Capel Horeb Quarry, Powys with Hostinella and irregularly shaped coalified patcha, some
of which may be .rVmatofhallus(NMW77.34G.28), x I . Figs 2, 3, 7. Macerated Nmatothallus cuticles;
category I . Fig. 2. (NMW 77, 34G,14a), x350. Fig. 3. (NMW77.34G.15a), x 350. Fig. 7. Fragment
comprising predominantly small units, but note two larger ones near top (NMW 77.%.356), x 320.
Figs 4-6, 8, 9. Film pulls of .Ncmatothallus cuticles; category 1. Fig. 4. Fragment of unusual shape
(.VMW 77.34C.16a), x 62. Fig. 5. Part of Fig. 4. enlarged, x 300. Fig. 6. (NMW 77.34G.17a), x 300.
Fig. 8. (NMW 77.3G.186), x250. Fig. 9. (NMW 77.34G.19), x250. Fig. 10. category 2 cuticle
showing typical cracking (.VMW 77.3G.21), x 100.
~
230
D. EDWARDS
NON-VASCULAR MICROFOSSILS FROM WALES
23 1
large conspicuous ones and others narrow and elongate. Blank units are extremely
well-developed. Flange width is 1.5-2.5 pm.
Specimen .NMW 7734G 22 is included for its extreme variability (Fig. 17). It is a
very pale piece of cuticle sporadically preserved on a film pull. Small clusters of
isodiametric units lie adjacent to areas similar in appearance to those described in
this category, where units are angular, but variable in size and shape. Occasional
larger units which are surrounded by a number of small ones appear rounded (see
unit arrowed in Fig. 18 for comparison) this effect being enhanced by the presence
of thicker flanges (4 pm). Elsewhere flange width is 1-3 pm, the thinnest being the
straightest .
Category 4 : Reticulum comprising units of wide size range with smaller members occasionally
forming a network around larger ones. Cuticle of unif0rm thickness (except atflanges) (Figs
18 20): This is the least satisfactory category and may well be an extension of
category 3 in which the distribution of large and small units seems to be random.
An excellent film pull example is illustrated in Figs 18 & 19. The smaller units
surrounding the more conspicuous larger ones may be isodiametric so that the
larger appear rounded, or elongate and parallel, with the larger ones more
angular. But such a patterning is not repeated over the whole area and other
regions resemble cuticles assigned to category 3 or even category 1. The cuticle
itself is well-preserved and of uniform colour except in the very smallest units. In
contrast, Fig. 20 shows a specimen in which, for the most part, flanges only are
present. Although these vary a little in width (1.5-2.0 pm) thicker forms are not
consistently associated with the larger units.
Category 5: Reticulum comprising units of varied shape and wide size range with smaller
members occasionally forming a network around larger ones. Cuticles thinner over the larger
units (Figs 21-26) : The conspicuous lighter units range from circular to oval to,
more rarely, rounded angular in shape and it is assumed that they possess a thinner
cuticle. This is most convincing in the cleared macerated specimens (Figs 21-23).
The size and distribution of the lighter units also varies, sometimes even on the same
piece of cuticle (Fig. 2 1 ). Very occasionally two adjacent units are separated by a
broad flange only, but more usually intervening areas are occupied by small
angular units which may be isodiametric or elongate. In one specimen oval units
occur within more extensive areas ofsmall angular units (Fig. 22). Flange thickness
may be more or less uniform or greater around the larger units. Unlike the film
pull specimens which cover a much wider area, these macerated examples are very
fragmentary, tend to be more variable and sometimes more difficult to interpret. A
typical example is shown in Fig. 24. Here most of the lighter units are almost
circular in outline, but some are oval or even more angular. Other members of the
category are characterized by conspicuous, predominantly circular, lighter units of
varying diameter.
In this category and the next some of the units appear perforate, although
Figures 11-22. .Vemutotha//w cuticles. Figs 11-14. Film pulls of cuticles; category 2. Fig. 1 1 . (NMW
77.34G.176), x250. Fig. 12. (NMW 77.346./66), x250. Fig. 13. Very dark cuticle with barely
distinguishable flanges (.VMW 77.34G.20), x 250. Fig. 14. (.VMW 77.%.21), ~ 2 5 0Figs
.
15, 17. Film
pull specimens; Fig. 16. macerated cuticle; category 3 Fig. 15 (NMW 77. 34G. 17c), x 250. Fig. 16.
(.VMW 77. iWC. 186), ~ 2 5 0 Fig.
.
17. (NMW 77.346.22), x 5 W . Figs 18 20. Film pull specimens;
Fig. 18. larger more
category 4. Figs 18, 19 illustrate two areas ofsame cuticle (NMW 77.34G.K~).
rounded units is indicated by arrow, x 250. Fig. 19. Larger units are more angular, x 250. Fig. 20.
(.VAfW 77.346.23). x 330. Figs 21, 22 Macerated cuticles; category 5. Fig. 21. Larger circular to oval
lighter units are not perforate (.VMW 77.34GM), x 500. Fig. 22. (NMW 77.34Gllc). x 500.
232
D. EDWARDS
NON-VASCULAR MICROFOSSILS FROM WALES
233
careful examination at higher magnification usually reveals vestiges of cuticle
attached to the flanges suggesting that the thinner cuticle above the larger units
has been torn off or weathered. The lighter units in specimen .NMW 77 3% 25a
(Fig. 25) range from oval to circular in shape. It is just possible to distinguish
smaller, more angular units in the intervening, very much darker areas. This is one
of the most informative pieces I recovered because attached to the fragment just
described is a smaller piece of very dark cuticle with faint patterning and cracking
typical of category 2 (Fig. 26). I have already speculated that certain cuticles in
this category are unevenly thickened.
Category 6: Perforate forms (Figs 29-33): Included in this category is a number of
diverse forms, mostly recovered on film pulls, and in which certain units lack any
traces of covering cuticle. The apertures are either perfectly circular, when they
tend to be most conspicuous, or can be subcircular or oval. Bearing in mind the
limitations of film pulls already mentioned, it is unfortunate that these forms are
not common in macerates. Indeed, I have found only one or two small scraps
where the cuticle appears to be pierced by circular holes (Fig. 27). Some cuticles in
this group may be closely related to those in category 5. Although the circular
lighter areas in Fig. 28 are smaller than in Fig. 25, the overall appearance is similar
and some of the units still bear traces of cuticle. However, others are considered to
be perforate. In Specimen NMW 77 .?4G 26d (Fig. 29) the lighter units are more
variable in shape and some of the larger oval perforations may extend over more
than one unit. Many of the cuticles are lighter and, except for the perforations, a
uniform colour. The imperforate areas may comprise rounded or angular units of
approximately the same size as the perforations. Flange width is more or less
uniform except where several circular units adjoin and blank units are extensively
developed. These lighter cuticles vary in the frequency and range in diameter of
the perforations (cf. Figs 30, 31, noting that these two forms were recovered from
the same piece of rock). Specimen .NMW 77 3% 27 (Fig. 32) stands apart in that it
comprises a reticulum of very small isodiametric units (range 3.0-8.0 pm; mean
6.0 [Am) with broad flanges of uniform thickness (4pm) so that the units have a
rounded appearance. Scattered throughout are circular to subcircular holes
slightly larger than the average unit diameter but bounded by flanges. A few show
peripheral cuticular remnants, but many have very clear cut boundaries and may
represent perforations in the original cuticle.
Finally there are some pieces of dark cuticle which are undoubtedly perforate
but lack many of the features of the above cuticles and may have had a different
origin. Fig. 33 shows an example where the holes are circular to subcircular
(diameter range 6.0-12.0 pm; mean 9.0 pm) and lie close together. I have not
been able to detect any structure in the intervening regions except for an
Figures 23 34. emulot lot hall^ cuticles. Figs 23-26,28. Imperforate forms; category 5. Fig. 23. Macerated
example (.VMW 77..?4C.15c), x IOOO. Fig. 24. Film pull (NMW 77.346.24), x 250. Fig. 25. Film pull
specimen showing traces of cuticles on margins of larger lighter units (.VMW 77.34G.25u), x 500. Fig.
26. Another part of this cuticle which merges into a darker region where units are much smaller, x 200.
Fig. 27. Poorly preserved macerated fragment with occasional perforations (NMW 77.343.144, x 500.
Fig. 28. (,VMW77.34C.26u), x 250. Figs 29-33. Film pulls of perforated cuticles; category 6. Fig. 29.
Darker cuticle with occasional often circular perforations (NMW 77.3fG.164, x 250. Fig. 30. (.N'MW
77.34.260), x 2.50. Fig. 31. (NAW 77.3&.266), x 250. Note that the circular perforations are more
frequent in Fig. 30 than in Fig. 31. Fig. 32. (.VMW 77.34C.27), x250. Fig. 33. (,VMW 77.34G.256),
x 250. Fig. 34. Part of cuticle illustrated by Lang (.Vn. KW.55, Plate 11, fig. 66) by kind permission of
the Keeper of Palaeontology, British Musuem (Natural History). Photograph by C. Shute, x 190.
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D.EDWARDS
NON-VASCULAR MICROFOSSILS FROM WALES
235
occasional small lighter area where the holes are further apart. In other specimens
the holes are less regular but more widely spaced, the cuticle itself being uniformly
dark.
SEMs of cuticles
.Vematothallus form: Some of these have already been mentioned (Figs 35-41).
Although very fragmentary, they tend to fall into two major groups. The first has
angular units and truncated, well-defined flanges (Fig. 38), while in the second the
flanges are longer, taper and enclose concave units with rounded outlines (Fig. 37).
The units are small and usually with a narrow size range, although Fig. 36
shows a fragment where a larger oval unit is also present.
Two objectives of this piece of research have been to discover something of the
morphology of the organism which secreted such cuticles and to learn something of
the underlying tissues. In pursuit of the first I have looked for well-defined
repeated units in film pull preparations and arrangement of units which may
constitute a margin (if indeed one existed). Where folding is observed (Fig. 35) it
may indicate that the plant had upper and lower surfaces enclosed by cuticles or
may even have been of tubular organization, but it seems more likely that such
folding is fortuitous and that the plant was thalloid, the conclusion reached by
Lang in 1937. In all but one of the specimens examined the edges are irregular.
The exception has a smooth margin and the flanges fade away to a flat border (Fig.
40).
The film pull specimens revealed little about underlying tissues. Although
coalified material may obliterate the pattern of flanges, I have never observed any
cellular organization in it. Very occasionally an isolated tube is adpressed to a
cuticle. To prevent destruction of more delicate tissues, cuticles for SEM
examination were not oxidized. In some cases this meant that granular, organic
but non-cellular, debris as well as quartz grains remained, trapped between the
flanges and often obliterating detail. Other specimens are cleaner with flanges
clearly visible, but a few have an untidy appearance (Fig. 43) because the flanges
are extended into flimsy, very irregular sheets, again lacking organization.
Specimen .MMW 77 34G 326 shows the most extensive subcuticular development
(Figs 44, 45) but even here it is impossible to detect either tubes or cells in the
‘stringy’ material. A very poorly preserved cuticle with adhering tubes is illustrated
in Fig. 46. A reticulum characteristic of .Nematothallus is still present in some areas.
The tubes may be part of the underlying tissue, but they look remarkably similar to
air-dried preparations of hyphae of Allomyces which had been prepared for
comparison with some of the smaller tubes to be described later. I therefore suspect
that this is recent fungal contamination which occurred either on the exposed rock
surface or during preparation.
Figures 35 42. Figs 35-41. SEMs of.Nmafothnlluscuticles. Fig. 35. Folded cuticle showing smooth and
flanged surfaces. Adpressed pollen grains are contaminants (NMW 77.346.290). x 425. Fig. 36. Inner
surface with short Ranges and shallow units: large unit indicated by arrow (NMW 77.3G.30). x 700.
Fig 37. Deeply concave units with rounded appearance; ?category 2, (.NMW77.3G.3/0).x 1450. Fig.
38. Reticulum with regular isdiametric units and clearly defined Ranges (.N.WV 77..?4C.33~),x 800.
Fig. 40. Inner surface of cuticle showing smooth margin (.NMW 77.34G.340), x 1100. Fig. 41. Inner
surface ofcuticle arrow indicates a regular blank unit (NMW 77.346.346), x 575. Fig. 42. Fragment of
coalified axis or inner surface of cuticle of vascular plant type (NMW 77.34C.3%), x 115.
236
D. EDWARDS
NON-VASCULAR MICROFOSSILS FROM WALES
23 7
Anomalousforms:
Specimen NMW 77 34G 33b (Figs 47, 48) : This is an irregularly-shaped fragment
15 pm thick with variable appearance resulting from differences in the
development of the flange system. Over small areas it resembles conventional
Nmothallus cuticles with high tapering flanges enclosing pronounced concave units
(Fig. 48). In other places the flanges are much broader, often appearing as flat
bands sometimes surrounding circular to subcircular apertures (c. 4 pm diameter).
The latter have rounded margins (Fig. 47) and give the impression that they lead
into chambers partially roofed by the flanges. This is difficult to substantiate in the
absence of sections, but such a degree of cuticularization is seen in certain
xeromorphic vascular plants where anticlinal epidermal walls are completely
cuticularized and the inner periclinal ones partly so (Stace, 1965; Fig. 1). Indeed
the faint ridges on some of the smaller flanges (arrowed in Fig. 47) may indicate
that still deeper tissues were cuticularized. Alternatively the fragment may be part
of a sheet of cells, but there is no evidence for this at the edges
" which could be
viewed (Fig. 48). In one region the single thick layer of cuticle is clearly perforated
(Fig. 48).
Speiimen NMW 77 34G 38a (Figs 52-54): Although superficially similar to the
previously described fragment, there is some evidence here for a sheet of cells.
Again the surface has a variable appearance. There are areas comprising a
reticulum of thick flanges with deep concave units (Fig. 54). The flanges may be
alternated with jagged edges or may be smooth and rounded (Fig. 53). In other
regions the surface is flat or may be interrupted by clusters of shallow concave
depressions of varying depth (Fig. 53). Fig. 51 shows a rounded aperture
surrounded by a smooth band sloping towards the hole, similar to those described
for specimen NMW 77 34C 336 (Fig. 47). Some of the fractured edges (Fig. 52)
indicate that the specimen possesses at least one layer of thick walled cells below
the exposed flanged surface described here.
Specimen NMW 77 34G 39a (Figs 5.558): The curved nature of this small fragment
made it possible to examine both surfaces, each of which bears a reticulate pattern.
The upper one (i.e. further away from the stub surface) shows aligned oval
depressions separated by more or less smooth flattened 'flanges', which may be
broader in some regions than others (Figs 55, 56). The lower one more closely
resembles the inner surface of .Nmatothallus-type cuticles (Fig. 58) but as this could
be viewed only at an oblique angle and the tilt of the stub has a profound influence
on the appearance of the upper surface, I cannot be certain that the two surfaces
are different. From the fractured edges (Figs 57, 58) adjacent upper and lower
depressions appear to be of equal depth and extend through almost the entire
thickness of the specimen. It was impossible to determine how such depressions
related spatially over a wider area.
Figures 43-50. Figs 43 46. SEMs of.Vemofofhollt*rcuticles. Fig. 43. Inner surface with flanges extended
into irregular sheets (.rVAfW77.346.34, x 1600. Fig. 44. Inner surface with underlying tissue (NMW
77.34G.326),x 160. Fig. 45. .Vnnatofhallus-typepatterning offlanges enlarged from Fig. 44, x 825. Fig.
46. Poorly preserved cuticle with attached tubes (.VMW 77.%G.296), x 400. Figs 47-50. SEMs of
anomalous forms. Fig. 47. Inner surface of cuticle showing broad flat flanges, some with faint ridges
(arrowed) ( VMW 77.34G.336), x 825. Fig. 48. Another part of cuticle illustrated in Fig. 47 showing
more typical .Vemufofhallus-type patterning. Perforation is indicated by arrow, x 700. Fig. 49. Thick
cuticle with faint reticulum and perforations (NMW 77.34G.31b).x 600.Fig. 50. Smooth cuticles with
depression and perforations ( VMW 77.34G.33, x 775.
238
D. EDWARDS
NON-VASCULAR MICROFOSSILS FROM WALES
239
Specimen NMW 77 34G 31b (Fig. 49): The thick cuticle illustrated in Fig. 49 is
characterized by a faint reticulum, absent from some areas, and prominent
circular perforations, (range 4-8.5 pm; mean 6 pm) in diameter. The latter may
occupy an entire unit, the centre of a unit so that a rim remains or may be
asymmetrically positioned. In one case a very thin film extends a short way from
the inner surface over the aperture. A few units bear circular darker areas which
correspond in size and position to the perforations in others. Although most of the
perforations extend vertically through the cuticle, a few are at an angle. Since the
cuticle is thick and the flanges poorly developed, it seems unlikely that such a
reticulum would be visible on film pull preparations.
Specimen NMW 77 34G 37 (Fig. 50) : This is an irregularly-shaped piece of cuticle
with smooth but gently wrinkled surface which seems to be perforate. The holes
occur in thinner cuticle at the bases of circular to oval depressions. They are
usually irregular in shape ranging from slits to larger jagged spaces, although in a
few cases the cuticle remains intact but often obliterated by detritus. This variation
suggests that the holes are produced as the thinner cuticle is worn away. However,
where they are circular with rounded edges and occupy the entire depression or
penetrate the cuticle at an angle (Fig. 50) it is possible they were present in the
original cuticle. There is some indication at a broken edge that the lower surface
was flanged, but no conclusive evidence to suggest affinity with Nematothallus.
DESCRIPTION OF TUBULAR ELEMENTS
Smooth Tubes:
Wideforms (20-40 pm) : The commonest types of tubular elements recovered on
bulk maceration in this group are unbranched and have very thick, almost smooth
walls (Figs 76, 77). These are probably melanosclerites (Eisenack, 1963) which are
of animal origin but of uncertain affinity. They are dark and do not respond to
prolonged exposure to Schulze's solution. In contrast there are short lengths of
wide tubes with thinner walls which do clear and may belong to plants. The walls
are featureless, the tubes compressed and unbranched (Fig. 78). When recovered
on film pulls they normally occur singly and appear as dark bands. An exception
is illustrated in Fig. 79 where a number of tubes show parallel alignment in an
amorphous, granular matrix. I could not detect any ornament in the short lengths
of dark presumed tube which ranged between 20 and 40 pm in diameter.
.Wurrora, forms ( < 6 p m ) : The largest fragments isolated on bulk maceration are
interwoven masses of small tubes, 3-5 pm in diameter. Before oxidation they are
almost black in colour and so densely organized that it is possible to see structural
detail only at the edges (Fig. 80). SEM and film pull preparations indicate that in
some cases the tubes are randomly interwoven forming mats ofsome thickness (Fig.
84) while in others (Fig. 85) they are more longitudinally aligned so that an axial
structure, several millimetres long results. Because the tubes are entangled and
fragment when teased apart, I could not convince myself from light microscope
Figures 51 58. SEM of anomalous cuticles. Figs 51-54. (NMW 77.34C.38~).Cellular layer with
variable surface patterning (for explanation see text) ; Fig. 51, x 750, Fig. 52, x 600,Fig. 53. x 725,
Fig. 54, x 775. Figs 55-58. Fragment ofcuticle with patterning on both surfaces (.NMW 77.34G.B~).
Fig. 55. Surface with oval depressions and rounded broad flanges, x 1400. Fig. 56, x 1250. Figs 57,58.
Edge of cuticle, Fig. 57, x 550. Fig. 58, x 1250.
240
D. EDWARDS
NON-VASCULAR MICROFOSSILS FROM WALES
24 I
preparations that they branch. The scanning micrographs show that they are
branched (Figs 87, 88), but sparingly so. They also indicate that the better
preserved tubes are smooth and parallel sided. Some of the macerated specimens
have less regular outlines and may be twisted or collapsed. Lighter oval or circular
areas (Fig. 83) may mark the scars ofbranches. I found no certain septa. Radiating
groups of tubes (Fig. 81) are sometimes seen in macerations, but these may be
fortuitous arrangements of superimposed elements.
Most of the tubes recovered from the macerates are dark coloured and give the
impression they are rigid structures. A small number are much lighter, less well
preserved and flimsy. The latter kind is most common on film pulls. As the
dimensions are the same, it is possible that the lighter forms are more weathered,
naturally oxidized examples of the darker.
Ornamented tubes: Banded tubes are very rare in Capel Horeb macerations. The
examples illustrated in Figs 74 & 75 show annular or spiral (with very low pitch)
ornamentation, the thickenings being 1-1.3 pm in diameter and 1-2 pm apart.
The very short lengths of tube recovered are unbranched, 25-30 pm in diameter
and occur singly. A group of tubes presumed to be of similar construction was
picked out for SEM studies (Figs 67-70). All except two of the tubes are
longitudinally orientated with some intertwining. The outer wall surface may be
smooth, gently contoured indicating the portions of the thickenings inside or
corrugated because of collapse of the thinner regions of the wall. T h e ornament
comprises inwardly projecting thickenings of the wall. These are continuous with
the wall and appear to be made of the same material. Whether or not the
thickenings are annular or spiral cannot be determined. They are 0.75-1.3 pm
wide and up to 3 pm apart. In cross-section they are semicircular with sometimes a
slight constriction where attached to the wall. The tubes are unbranched and not
tapered.
A second group of tubes is illustrated in Figs 71 & 72. Specimen NMW 77 3415
38c is a small irregular fragment, just over a millimetre long and 400 pm wide
comprised of aligned tubes which show a tendency to fracture longitudinally and
to split into sheets. The presence of longitudinally thinning ridges and sporadic
more or less transverse folds give the surface a scalariform appearance. Where
intact, the tubes are c. 12.5 pm diameter and are of one kind. Their inner surfaces
show a reticulate patterning which may be an original feature or may have been
produced by pyrite crystals. A similar patterning which I am more convinced is
pyrite damage is seen in Fig. 73. Additional material is required to permit a more
detailed investigation of this type of organization. I have included it to
demonstrate the diversity in the microfossil assemblage.
Association of tubes: Most of the mats of tubes recovered on bulk maceration
consisted of small tubes of one size only. Figure 82 shows an exception, a very
fragmentary specimen in which larger tubes are also present. Film pull
Figures 59-66. SEMs of Proiotaxifes-type associations of tubes. Figs 59 62 (,VhfW77.34G.3k). Fig. 59.
Fragment showing conspicuous longitudinally orientated wide smooth tubes, x 140. Fig. 60.
Transversely fractured tubes showing completely homogenous wall system, x 1100. Fig. 61. Wide tube
fractured longitudinally revealing smooth inner surbce of wall, x 1200. Fig. 62. Transverse fracture
showing discrete tuhes, x 1100. Figs 63 65 (.MhfW 77.34G.34~).Fig. 63. Small fragment with one
conspicuous intact tube, x 150. Fig. 64. Transverse fracture with numerous wide tubes, x 450. Fig.
65. Longitudinal fracture showing one intact wide tube surrounded by apparently disorganized tissue
in position of smaller tube system, x 325. Fig. 66. l’ransversr fracture where discrete tubes are not
evident and wall systems arc completely homogenous (.V.Z4W 77.344G.386), x 1250.
16
242
D. EDWARDS
NON-VASCULAR MICROFOSSILS FROM WALES
243
preparations are a little more informative. In one case a few, poorly preserved
featureless ‘bands’ (c. 16 pm diameter) lie beneath a mass of small tubes of the
lighter variety (Fig. 89), but it is impossible to decide whether or not such an
association is fortuitous. The wider tubes (10.4-31.2 pm: mean 16.3 pm) in
specimen .NMW 77 34G 50 are more numerous and roughly aligned in a matrix of
granular coalified material and short lengths of poorly preserved, but apparently
unbranched tubes (2.6-5.2 pm diameter) which are either randomly arranged or
show some longitudinal orientation parallel to the wider tubes (Fig. 90). The latter
are unbranched, dark, straight or slightly sinuous and up to 270 pm long. I
thought initially that they were similar to the featureless smooth forms described
on page 239, but there are occasional very short lengths of tube which are clearly
banded (Fig. 93). Closer examination of the dark kinds and photography with
infra red film revealed that some are also ornamented. I cannot be sure that all the
wide tubes are of this kind as there are also a few, lighter-coloured, structureless
bands associated with the narrow tubes.
Fragments in which wide tubes predominate: These are known only from SEM studies
and superficially resemble Prototaxites. The first, a small fragment c. 400 pm long, is
composed of longitudinally orientated, thick-walled tubes, smooth on the inside,
and usually slightly compressed. Tube diameter is c. 20 pm and wall thickness,
3 4 pm. Where adjacent tubes are in contact the walls are completely fused and so
the cell wall system appears homogeneous (Fig. 60). In fractured cross-section
(Figs 60, 62), the wider tubes appear separated by a system of smaller elements
where again the walls show homogenization although here the walls are much
thinner. Fractured surfaces at right angles to this reveal a three-dimensional
reticulum apparently formed by irregular extensions of the walls of the larger tubes
(Fig. 61). The unexpected appearance of the intervening tissue may result from the
homogenization of the walls of a system of small tubes (pseudoparenchyma of some
authors, e.g. Schmid, 1976) although I fail to find any distinct channels in the very
disorganized tissue.
Similar general organization and state of preservation are seen in the specimen
illustrated in Figs 63-65. Many wide tubes are visible in transverse section, but the
fragment is very short and only one intact tube with ‘flanged’ surface is preserved
in the fractured longitudinal plane (Fig. 61) The rest of this surface appears
completely disorganized, with again little evidence for a second system of narrow
tubes.
In the last example in this group, the wall system is completely homogeneous so
there are no discrete tubes. One fractured surface (Fig. 66) shows large oval
lumens, each delimited by a narrow structureless layer, interpreted as a thick wall.
This is continued into a reticulum in which the holes are much smaller than
previously described. The surface at right angles to this is contoured indicating the
positions of the longitudinally running under tubes, although the surface itself
Figures 67-74. Ornamented tubes. Figs 67-70. Banded tubes ( ~ V M W77.34C.33).Fig. 67. Cluster of
tubes, the majority longitudinally orientated, x 140. Fig. 68. Ridged inner surface of broken tube,
x 3125. Fig. 69. Inner surface of tubes showing irregularly spaced thickenings and smooth outer
surface at bottom right, x 3000. Fig. 70. Note corrugated appearance of outer surface of tube, where
collapse has occurred between thickenings, x 1200. Fig. 71. End of fragment composed of tubes with
scalariform surface appearance ( N M W 77.34G.34,x 120. Fig. 72. Another part ofspecimen illustrated
in Fig. 71 showing surface and reticulate patterning on inner wall, perhaps the results of pyrite
damage, x 362. Fig. 73. Tubes with internal pitting produced by pyrite (NMW 77.%.4J), x 500. Fig.
74. Isolated ornamented tube recovered on bulk maceration (.VMW 77.346.357,x 625.
244
D. EDWARDS
comprises an irregular, three-dimensional reticulum. Limited observations on the
inner surfaces of the tubes suggest that they are not as smooth as in the other
examples.
Homogenization of the cell wall system is a characteristic of charcoalified plant
fragments and the presence of charcoal in younger sediments has been used as an
indication of oxygen levels in palaeoatmospheres (Cope & Chaloner, 1980).
However, in the specimens described here, it seems unlikely that the peculiar
preservation results from burning, although it could have been produced by low
grade burial metamorphism, the lack of compression in the fragments perhaps
reflecting an unusually resilient wall composition. (Both Pachythecu and Prototuxites
are frequently recovered relatively uncompressed in Silurian and Devonian
assemblages where the remaining plants are completely flattened). Alternatively,
as cell wall homogenization is not seen in all the plant fragments at the locality
(e.g. the weft of small tubes), the wall system illustrated may have been present in
the original plant. Finally, it is possible, but considered improbable, that the effect is
a preparation artefact.
COMPARISON WITH SIMILAR MICROFOSSILS FROM SILURIAN SEDIMENTS
It was Lang (1937) who first described and appreciated the importance of such
microfossils which he had isolated from very fragmentary plant debris, remains
which “might often be regarded, not unjustly, as so broken up and decayed as
hardly to repay collection and examination’’ (Lang 1937: 247). In that paper
based on localities throughout the Downtonian he recorded cuticles with a
pseudocellular pattern and tubes of two sizes, the wider with internal thickenings.
Their frequent association led to the conclusion that they belonged to a single
organism which Lang called Nemutothullus. The validity of this will be questioned
later on, but I have no doubt that the microfossils themselves are similar to those I
have just described.
Considering first his figured cuticles, some are so familiar that they may be
assigned to one of my categories, e.g. No. 807 (Lang, 1937 : pl. 10, fig. 52) and .No.
765 (pl. 11, fig. 66) are typical of category 1 and No. 992 (Lang, 1937: pl. 11, fig.
67), of category 5. The specimen No. 807 (Lang, 1937 : pl. 11, fig. 64) in which the
units are mainly rounded with predominantly thin flanges, is less familiar.
However, Lang had much greater success in clearing his specimens on cellulose
nitrate films than I, and it is possible that some of his paler cuticles with faint linear
flanges, correspond to some of the darker film pull specimens I have described, e.g.
in category 2. In some of his cuticles the patterning is not uniform over the whole
specimen, The film transfer preparation from the Temeside Shale already
mentioned (V. 54655) bears a number of large, well-preserved pieces of cuticle,
most with a regular pattern of clearly-defined flanges similar to that of category 1.
In certain areas the reticulum is less distinct and highly variable with some broad
flanges surrounding more rounded angular or even circular units. The cuticle here
is sporadically darker and appears to be thicker, perhaps comprising more than
one layer. SEM studies have not yet been undertaken on the Temeside Shale, but
it is possible that such areas correspond to the anomalous fragments I have
illustrated in Figs 51-58 and that Lang’s evidence for a thick-walled epidermal
layer (Lang 1937: 265) came from sections through such fragments.
Lang (1937) also found wefts of entangled small non-septate tubes, sparsely
NON-VASCULAR MICROFOSSILS FROM WALES
245
branched and averaging 2.5 pm diameter (range 1-5 pm) which closely resemble
those I have figured (Figs SCr88). Some of these cover a considerable area (e.g.
Lang, 1937: pl. 11, fig. 63 is 20 mm long by 5 mm wide) and the triangular
encrustation (Lang, 1937: pl. 12, fig. 83) has a maximum length of 35 mm. In
some specimens, he demonstrated the presence of wider tubes among the smaller
ones, although in these cases the latter tend to be less well-preserved, again
paralleling my own observations. No. 961 (Lang, 1937: pl. 11, fig. 57) is
superficially similar to NMW 77 34G 50 (Figs 90-93) but Lang was not able to
show banding in the darker wide tubes, although in another specimen from
Freshwater East (No.962) banded tubes are clearly present (Lang, 1937 : pl. 1 1, fig.
60). He also recorded isolated examples of wide featureless and banded tubes, of
similar size to those I have described.
Although I have found an occasional spore caught up in a tuft oftubes and a few
spore masses on bulk maceration and spores have been recovered from rock
surfaces or more rarely adpressed to cuticles on film pulls, I have found no
evidence to support Lang’s conclusion that they belong to the same plants as the
cuticles and tubes.
Interest in such fragmentary remains was revived in the last decade by, for
example, Gray & Boucot (1971, 1977, 1978) Gray, Laufeld & Boucot (1974) and
Banks (1975a, b, c) as their relevance of Silurian occurrences of vascular plants and
to the earliest land plants was debated. Banks (1975a) illustrated three cuticular
fragments, two of which had been isolated from early Silurian (Llandovery)
sediments of New York State by Professor W. Evitt. The third is one of my
preparations from the Siegenian of S. Wales. The latter I would assign to category
1. Considering the two North American specimens, Banks, 1975a: pl. 11, fig. 1
belongs in category 3 and Banks, 1975a: pl. 11, fig. 2, in category 2. In the same
paper Banks summarized records of dispersed banded tubes and of the two he
figured, the Llandovery specimen from New York State (Banks, 1975a: pl. 1, fig.
2) closely resembles those here.
By far the most comprehensive recent account of a similar assemblage of
microfossils, isolated by bulk maceration of continental Llandovery sediments from
Virginia, U.S.A.,is given by Pratt et al. (1978). The older strata yielded far greater
numbers of unbranched, non-septate, banded tubes. These occurred singly, in
pairs or in clusters of up to eight tubes aligned in parallel. They varied in width,
type of ornament (spiral or annular) and distance apart of bands. The Cape1
Horeb specimens fall within their size range and correspond to certain forms of
patterning. Their SEMs (Pratt et al., 1978: pl. 1, figs 11, 13) showing the internal
ridging of the wall are similar to my Figs 67-70 but differ in relative dimensions.
The most exciting discoveries of the American workers were the tapering tubes
with annular thickenings and intact ends. They illustrate one where the tube
narrows into a neck which is further extended into a papilliform tip.
Also found was a variety of smooth wide tubes described as “imperforate,
aseptate and unbranched” (Pratt et al., 1978: 129). These again are of similar size
to the Welsh specimens. More decayed examples showed faint oblique striations
which I have never observed, but which Strother & Traverse (1979) have recorded
on similar-sized tubes from contemporaneous sediments from Pennsylvania (see
below).
Dense wefts composed of variable, sparingly-branched tubes, called hyphal
filaments, look superficially similar to the specimens I have illustrated in Figs
246
D. EDWARDS
NON-VASCULAR MICROFOSSILS FROM WALES
24 7
84-88 but the older tubes are slightly wider (mean 6.0pm) and occasionally
septate. These septa and associated branching points are so distinctive that I doubt
I would have overlooked them had they been present in the Welsh material. The
authors emphasized that the hyphal filaments ere never found associated with
wider tubes or adpressed to cuticles.
A further important difference lies in their interpretation of some cuticular
fragments described as membranous, cellular sheets. Again, superficially they
resemble some of the cuticles from Capel Horeb. The SEM (Strother & Traverse,
1979; fig. 2), using my terminology, shows the inner surface of a cuticle on which
flanges are well-developed and delimit deeply concave units. There is also
considerable extraneous material which may represent the remains of underlying
tissues. However, Pratt and her co-workers interpreted my ‘flanges’ as cell walls
which jut outwards and the extraneous material as ‘thinner intracellular material’
(Pratt et al., 1978: 133). In addition, they suggested that there was a further noncellular cuticle layer covering the projecting walls. It is possible that their
micrograph, of an essentially smooth cuticle bearing faint impressions of cells,
corresponds to the outer face of a cuticle of the kind I have described, but I am
reluctant to speculate further on specimens which I have examined only from
photographs.
Strother & Traverse (1979) published a preliminary account ofmicrofossils from
Llandovery and Wenlock sediments of Pennsylvania, U.S.A. This was concerned
mainly with palynomorphs but they also described tubular and cuticular
fragments, the figured specimens coming from Wenlock strata. Microfossils from
the older horizon included compressed, featureless non-septate tubes, 8-12 pm in
diameter and a couple with annular thickenings. The cuticles were described as
possessing a ‘reticulate pattern of ridges’ (Strother & Traverse, 1979: 14) and the
units in some were perforate. The Wenlock assemblage was more diverse. I n
addition to the small tubes (mean diameter 10 pm), they recovered isolated wide
tubes which could be distinguished by their wall patterning. The forms they
figured with annular and spiral banding are similar in organization to some of
those from Virginia and from Capel Horeb (see, for example Strother & Traverse,
1979: pl. 3, figs 15, 18). They also illustrate a short piece of tube in which the
thickenings appear to project from the outside of the wall and other wide tubes
where walls are obliquely striated or appeared granular. The piece of cuticle
photographed by transmitted light shows a reticulate patterning but is too small to
categorize. Far more informative is the SEM in which the cuticle is folded so that
both surfaces are visible. The inner bears very prominent, broad flanges enclosing
angular but rounded units, some of which appear deeper than others. The
positions of the units are marked by shallow depressions on the otherwise smooth
Figures 75 -85. Fig. 75. Macerated tube showing annular thickening, (,VMW 77.34C.33, x650. Figs
66, 77. Fractured ends of unbranched tubes with thick, structureless walls, probably melanosclerites
(i.e.animal). Fig. 76. (.VMW77.34G.29~),
x 1350. Fig. 77. (.NMW77.34G.33d), ~ 4 6 2 Fig.
.
78. End of
featureless compresed broad tube believed to be of plant origin (.VMW 77.346.4223, x 950. Fig. 79.
Film pull with broad longitudinally orientated ?tubes in amorphous matrix (.VMW 77.34G.49,
x 120. Fig. 80. Typical mass ofsmall tubes recovered from bulm maceration with elements visible only
at the edge (.VMW 77.34G.46), x 120. Fig. 81. Edge ofmat of tubes with radial arrangement (.VMW
77.34C.47), x 350. Fig. 82. Fragment recovered on bulk maceration with tubesoftwosizes, both smooth
(.brMW 77.34G.46), x 200. Fig. 83. Teased-out tubes with irregular outline and showing lighter areas
(,+’.ifW 77.346‘.48), x 410. Figs 84, 85. SEM of small tubes. Fig. 84. Tubes interwoven randomly
(.V.tfW 77..M;.43a), x 350. Fig. 85. Tubes mainly 1ong.itudinallyaligned (.WMW 77.3#G.43b), x 460.
248
D. EDWARDS
Figures 86-93. Fig. 86. Fragment of t u b a partly embedded or adpressed to amorphous material
(.NMW 77.34C.44), x 200. Figs 87, 88. Tubes with branching (NMW 77.34C.43),x 1400. Fig. 89.
Film pull with weft of predominantly small tubes and occasional featureless wide ones (arrow) (.NMW
77.34C.49), ~ 3 5 0 Figs
.
90-93. Film pull, specimen composed of wide and narrow tubes (NMW
77.34C.50). Fig. 90.General view with two apparently featureless dark wide tubes in matrix of small
ones, x 200. Fig. 91. Arrow indicates wide tube with ornament, x 375. Fig. 92. Part of matrix of
narrow smooth tubes, x 375. Fig. 93. Part ofdark wide tube with some indication ofornament, x 800.
upper surface. This morphology does not exactly match any of my categories but
may be intermediate between 2 and 5. Strother & Traverse (1979: 19) interpreted
the cuticles as “extracellular secretions of unknown composition by
parenchymatous tissues of a plant thallus”.
NON-VASCULAR MICROFOSSILS FROM WALES
249
A similar assemblage (palynomorphs, cuticles and tubes) was recovered by
McGregor & Narbonne (1978) from late Ludlow sediments ofArctic Canada. The
mainly banded tubes have no counterparts in the Welsh material, but of the two
figured cuticles described as cellular sheets, one (McGregor & Narbonne, 1978: pl.
2, fig. 3) is identical to certain members (Fig. 23) of category 5 and the other has
characteristics of categories 1 and 2. They also illustrated some fragments of
arthropod cuticles some of which I have found at Capel Horeb. Zdebska (1978)
described some perforated cuticles from the Lower Devonian of Poland which she
assigned to Spongiophyton. Her illustrations of Spongiophyton sp. 2, which include
some excellent SEMs of both surfaces of quite large fragments, look similar to
cuticles of the kind I have categorized above and which Lang (1937) called
.,Vaatothallus. T h e cuticular patterning in Spongiophyton (Chaloner, Mensah &
Crane, 1974) is quite different. It is unfortunate that the specimen which shows
dichotomizing branching (Spongiophyton sp. 1 ), and superficially resembles a
Spongiophyton thallus, lacks both cellular detail and any convincing evidence for
tubular construction. The cuticles with reticulate patterning and perforations have
more in common with those isolated from younger sediments in Britain (work in
progress in Cardim.
T o sum up, the majority of the microfossils which I have isolated and described
can be identified by reference to Lang’s work on Downtonian floras, while more
recent work indicates that similar assemblages occur throughout the Silurian and
extend into the Lower Devonian.
TAXONOMIC STATUS OF THE MICROFOSSILS
Lang (1937) believed that the repeated association of cuticles, banded and
narrow tubes pointed to their all belonging to the same organism which he named
.Vematothallus pseudo-vasculosus. He concluded that it was a land plant of
organization not paralleled elsewhere in the plant kingdom. In that Prototaxites,
another putative land plant of enigmatic affinity, also possessed two systems of
tubes, Lang placed both in a new class, the Nematophytales, but felt that there was
some justification for erecting a new phylum to include land plants intermediate
between the algae and vascular plants “with an organisation that proved
unsuccessful so that they became extinct” (Lang 1937: 287). He further speculated
that since both genera often occurred in the same assemblages throughout the
Downtonian they may have been different parts of the same plant, but he had no
direct evidence for this. The suggestion has recently been revived by Jonker (1979)
who has attached thalloid .Nematothallus to axes of Prototaxites construction.
My own investigations at Capel Horeb have yielded no additional evidence to
support Lang’s conclusion on the tripartite nature of .Nematothallus. Although I
have recovered associations of two sizes of tubes, they have never been attached or
adpressed to cuticles. Lang provided very detailed descriptions of his most
informative specimens which I have recently re-examined. Most are film transfers
prepared by coating the rock surface and compressions fossils with a thick layer of
cellulose nitrate in amyl acetate and, after drying, dissolving the rock in
hydrofluoric acid. The buried surfaces of the compressions are thus exposed on the
cellulose nitrate film. This has the advantage of causing less damage from tearing
than the film pull technique b u t where the original rock surface was particularly
rich in plant fragments, layers of superimposed cuticles and tubes together with
250
D. EDWARDS
some persistent rock grains may be recovered. Lang’s specimens from Freshwater
East, Dyfed (Pembroke) and Tin Mill Race, Shropshire, provide good examples of
this. Although occasionally, a small number of wide featureless tubes are
superimposed on cuticles or patches of very poorly preserved small tubes adjoin or
are adpressed to cuticles I am convinced that such occurrences are fortuitous.
However, there is very good evidence for the associations of two sizes of tubes in the
Lang preparations (Lang 1937: pl. 11, figs 57, 60). Pratt et al. (1978) record three
very fragmentary specimens in which a small number of banded tubes is said to be
embedded in cellular sheets. Nevertheless, I propose to discuss the affinities of tubes
and cuticles separately here and to avoid confusion I propose that the genus
Nmatothallus be used for thalloid or foliose compressions which are covered by a
cuticle bearing a reticulate patterning of flanges, and that this name should not be
used for associations of tubes. Until the significance of the patterning of flanges in
terms of the organization of underlying tissues is appreciated, I am reluctant to
delimit a number of species even though there is a striking variation between some
of the cuticles I have described. The six categories were erected to facilitate the
handling of a large number of specimens and were not intended as natural
groupings. Those specimens which encompass more than one category vindicated
this approach. Progress in elucidating the nature of the underlying tissues has been
disappointing but perhaps this was to be expected. If the role of such cuticles was
to protect ‘soft’ tissues vulnerable to desiccation the latter would presumably have
had little potential for fossilization.
AFFINITIES AND NATURE OF NEMATOTHALLUS
Apart from the cuticles from North America and Poland which I have already
surveyed above and believe to be related to Nematothallus as defined
here, there are records of non-vascular plants throughout the Devonian which
possessed ‘cuticles’ or an outer layer of thick-walled cells and which are considered
to have been adapted to the terrestrial environment. These were reviewed by
Chaloner et al. (1974), whilst a more recent paper by Niklas (1980) summarized
the role of palaeobiochemical studies in deducing their affinities.
I have examined preparations from two of these plants, Parka decipiens (Lower
Devonian, Scotland) and Orestovia devonica Devonian : U.S.S.R.) and found
nothing to suggest relationship with Nematothallus. The sac-like, sometimes forking,
thalli of Protosalvinia (Foerstia) have a surface cellular patterning, but Schopf (1978)
emphasizes that the resilient covering is not a cuticle, but a single layer of thickwalled cells. .Nematothallus has far more in common with Spongiophyton in which a
very thick cuticle bears the imprints of cells on its inner surface. Two species were
originally recorded from the middle Devonian of Brazil (Krausel, 1960) and these
have more recently been described from Ghana by Chaloner et a f . (1974). The
thallus of Spongiophyton is a flattened, cylindrical, dorsivential dichotomizing
structure in which the upper cuticle, perforated by large holes, is much thicker
than the lower. The cellular patterning on the inside of the cuticle is usually very
regular with longitudinally orientated ranks of elongate units quite distinct from
that in Nematothallus. Some SEMs (e.g. Chaloner et al., 1974: 121, figs 2, 3) are
superficially similar but the units are much larger and the cuticles thicker. The
tubular construction of Spongiophyton has not been convincingly demonstrated for
.Nematothallus.
NON-VASCULAR MICROFOSSILS FROM WALES
25 1
I n the absence of any closely related forms in the fossil record and of any wellpreserved tissues below the cuticles, the affinities of the plants covered by
.R'ematothallus cuticles remain obscure. Nevertheless it is still possible, to speculate
on the nature of the underlying tissues by reviewing the surface features of a wide
variety of plants which would produce a Nmatothallus-type patterning on
superimposed cuticles. This approach is not new : it was adopted by Chaloner et al.
(1974), in deducing the nature of Spongiophyton and also figured in assessments on
the affinities of cuticles in the early land plant debate (Banks 1975 a,b; Gray &
Boucot, 1977, 1980).
I begin by assuming that .Nmatothallus was a thallose, perhaps encrusting, plant
whose upper surface only was probably covered by a cuticle. Although other
possibilities, namely that it comprised a flattened tubular thallus or was foliose,
have been considered, I have no evidence for either. O n land the thalloid habit is
seen in the majority of fern gametophytes and in many liverworts, although the
arrangement of surface cells tends to be more orderly than in Nmatothallus. A far
greater range of tissue types is found in the algae, where I have paid particular
attention to encrusting forms. Marine examples from the Rhodophyta include
multiaxial growth forms in which a thin thallus is composed of horizontal filaments
which produce short, upwardly directed files of cells, the surface layer comprising
the tips of the latter. In certain thallose Phaeophyta (Fucales) a distinct surface
layer, the meristoderm, is delimited. Extracellular surface layers may be present in
extant red and brown algae, but these differ in composition from vascular plant
cuticles and would probably not persist in coalified compressions. Lang (1937)
himself entertained the possibility that organization typical of the Codiaceae could
have produced the patterning on his Nmatothallus cuticles. In these algae
coenocytic filaments are entwined to form axial cables and then turn outwards to
stand at right angles to the surface. Lang rejected this idea and suggested that the
patterning was produced by the pressure o f a network ofsmall tubes on the cuticle.
He changed his mind again (Lang, 1945) after preparing a section through a thickwalled epidermis, but this was not illustrated.
Having very briefly surveyed the literature and made a few preparations from
representatives of the major algal lines, I favour a patterning produced by the ends
of closely packed filaments or siphons as is seen in certain green algae rather than a
discrete epidermal layer covering parenchymatous or pseudoparenchymatous
tissues. I must emphasize, that this opinion relates only to the organization of
underlying tissues and has no taxonomic implications.
In a recent paper, Edwards, Edwards & Rayner (in press) deliberated on the
roles and physiological consequences of an imperforate cuticle. There is now some
evidence to suggest that a few cuticles are perforate, although whether or not
imperforate and perforate forms derive from the same organisms cannot be
determined. Thinner areas over certain units which characterize category 5
cuticles may have facilitated gaseous exchange or may mark the positions of
underlying sporangia or gametangia.
Some of the perforate cuticles cannot be assigned to Nmatothallus and may well
be of arthropod origin. Fragments of eurypterid cuticle showing the characteristic
scales are occasionally recovered on film pulls from Cape1 Horeb. McGregor &
Narbonne (1978) figure a variety of such fragments of diverse origin : their fig. 4b
shows a pale cuticle with a faint reticulum and occasional perforations which is
superficially similar to some of my figures. They tentatively relate this to a
2.52
D. EDWARDS
ceratiocaridid crustacean (Rolfe, 1962) although Gray & Boucot (1977) doubt
that cuticles composed of collophane with some replacement calcite would survive
acid oxidation treatments. Rolfe’s paper is useful in that it lists a wide range of
organisms and processes capable of boring or perforating cuticles or shells. In the
current investigation I have looked very carefully at the perforated forms for
indications of such secondary structures. The most spectacular example of the
activity of a borer at the Capel Horeb locality is seen in the perforated tests of
Dictyocaris. These large encrustations, covering several square centimetres, with
characteristic polygonal surface markings and conspicuous perforations (5 mm in
diameter) were originally thought to be of plant affinity (Thallomia: Heard &
Jones, 1931). Chaloner et al. (1974) reiterated Lang’s doubts (Lang, 1937) that the
cuticles with convincing stomata and fragments of vascular tissue had been isolated
from the fossils. in the meantime, Rolfe (1969) had placed Thallomia in synonomy
with Dictyocaris a phyllocarid arthropod, whose test is often characterized by large
perforations (Stamer, 1935). Having applied all the techniques outlined above to
the Capel Horeb specimens, I can confirm that they lack any structures indicative
of plant affinity.
AFFINITIES AND NATURE OF TUBULAR ELEMENTS
Lang (1937) emphasized that a major difference between Prototaxites and his
.Nematothallus was the presence of banded tubes in the latter. However, he had
earlier been involved in the description of the only species of Prototaxiles, P . taitii, in
which spirally thickened tubes are recorded (Kidston & Lang, 1921). Associated
with a small fragment composed of unornamented tubes of two sizes, the larger of
mean diameter 40 pm and the smaller 10 pm, they found another piece which they
interpreted as the peripheral region of a cylindrical structure. It was in the inner
zone of this that they recorded fine tubes with spiral ornament comprising a
ridging of the inner surface of a thick wall, similar in construction to the wide tubes
I have isolated. No dimensions were given, and they were unable to demonstrate
connection with more typical Prototaxites axes, where the two sizes of tubes
possessed walls of uniform thickness, with the wider thick-walled forms orientated
in a predominantly longitudinal direction.
Lyon (1962) discovered a second Rhynie Chert example which comprised a
loose plexus of randomly orientated, non-septate tubes of two sizes, in which the
smaller (mean diameter 8.5 pm) had smooth walls and the larger (range 2-24 pm;
mean 18 pm) possessed thick walls with conspicuous spiral thickenings. Branching
in both types was restricted to small areas called branch knots (possibly equivalent
to the medullary spots of Prototaxites). Lyon also found much wider smooth tubes
(56 pm diameter) in associated fragments. The ornamented tubes are very
distinctive and quite different from those of Nmatothallus sensu Lang, those I have
described here and those attributed to Prototaxites taitii. Indeed, Lyon created a
new taxon Nematoplexus rhyniensis. He suggested that his new genus should embrace
“fragments of ‘tube tissue’ which cannot (within the limits of existing knowledge)
be assigned to either Prototaxites and Nematothallus” (Lyon 1962 : 85). Nmatoplexw,
a form genus for associations of two sizes of aseptate tubes the smaller with smooth
walls, the wider with internal ornamentation derived from an organism of
unknown form and size, would encompass many of the systems of tubes which
NON-VASCULAR MICROFOSSILS FROM WALES
253
Lang (Lang, 1937; pl. 11, figs 55-61) and I (Figs 89-93) have described, although
I should like to find additional specimens before delimiting species.
Lang ( 1937), together with subsequent authors, suggested that his Nmatothallus
could have been attached to axes of Prototaxites but had no direct evidence for this.
More recently, Jonker (1979) described thalli composed of fine tubes traversed by
dark wide tubes (veins) in which annular thickenings were detected. These, which
he identified as .Nmatothallus and termed phylloids, were found attached to axes of
Prototaxites construction (termed cauloids) except that some of the larger tubes
were ornamented. Jonker called his reconstructed plant, Prototaxites loganii
although ornamented tubes are not a characteristic of this species. Dawson (1859)
had originally described the large tubes as being spirally thickened, but it was later
shown that the system of small tubes itself had produced this effect, (Carruthers,
1872). Some of my preparations, i.e. those associations of tubes which I would call
.Irematoplexus, correspond to Jonker’s descriptions of Nematothallus - phylloids, but
as he gives no measurements and his preparations are ground sections, comparison
is difficult. Cuticles are not recorded in the new German specimens and this
illustrates the ambiguities which may arise in the use of Nmatothallus semu Lang.
I have no evidence to support the attachment of associations of tubes described
here to Prototaxites, which is also recorded at Capel Horeb. Apart from identifying
the latter in late Silurian sediments, I have somewhat neglected this genus. The
apparent incompressibility of these specimens and my SEMs showing
homogenization of the wall system indicate the necessity for more detailed
investigation. Lang (1937), of course, had been more thorough and had embedded
and sectioned his Downtonian material. Large tubes are conspicuous in his
transverse sections and they broadly correspond in diameter to the tubes described
here and were all smooth walled. He noted that the distance between the wide
tubes and hence amount of tissue comprising small tubes varied between
specimens, a feature illustrated by Krausel & Weyland (1934: fig. 21) for
Prototaxites dtchenianus from the Lower Devonian of Germany. Jonker ( 1979)
identified their fig. 3, a longitudinal section through a n axial structure, in which
the wide tubes are smooth, as .Nematothallus.
There remain the relationships and affinities of isolated ornamented tubes,
clusters of such tubes and the wefts of narrow tubes. My meagre evidence suggests
that the isolated ornamented forms are similar to those associated with the fine
tubes. Lang thought that the wider ones were increasingly concentrated to the
interior, perhaps even associated to form conducting tissue (Lang, 1937; Pratt et al.
1978) while the smaller ones predominated at the edges. I am less confident that all
the narrow tubes I have isolated come from the same type of organism. Masses of
small tubes (sparingly branched) and with smooth walls are very common at some
localities where banded tubes are absent. When considering possible mycological
affinities of such tubes from the Brecon Beacons Quarry (Lower Devonian) I sent
some preparations to Dr Pirozynski but he could not find any characteristics which
would allow unequivocal assignment to the fungi.
The functions and affinities of the ornamented tubes have recently received
considerable attention (Banks 1975 a,b; Gray & Boucot 1977; Pratt et al., 1978;
Schopf, 1978). The diversity of forms recorded by Strother & Traverse (1979)
suggests that they come from a number of organisms. I can add little to the debate.
I believe that the tubes, except the melanosclerites I have recovered, are all of
plant origin although I cannot be certain that they derive from the same kind of
254
D. EDWARDS
plant. My SEM studies suggest that the ornament is an internal ridging of the wall,
is of the same composition as the wall and is continuous with it. Having observed
the homogeneous wall system in Prototaxites I am now more hesitant to state
categorically that the banded tubes are quite different from xylem conducting
elements where the primary wall remains unthickened, especially as Strother &
Traverse (1979) and Lang (1937) mentioned that their thickenings were easily
dislodged. However, from my experience with tracheids from coalified
compressions in late Silurian and early Devonian sediments where the primary
wall is never preserved, I am convinced that the unthickened parts of the banded
tubes are not composed of cellulose and hence that these structures are not
pteridophyte tracheids. Niklas & Pratt ( 1980) have isolated lignin or lignin-like
residues from the microfossil assemblage described by Pratt et al., (1978) and
suggest that “these plants may have had cell types that were both structurally and
biochemically similar to those of water conducting cells” (Nicklas & Pratt, 1980:
396). These geochemical data were based on the entire assemblage and so it was
not possible to prove that the lignin residues came from the banded tubes
themselves.
CONCLUSIONS
The microfossils (cuticles and tubular elements) described here are similar to
those recorded throughout the Silurian and Lower Devonian.
Many correspond to the remains described by Lang (1937) when he erected the
genus Nmatothallus. I suggest here that .Nmatothallus be restricted to thallose
compressions in which it is possible to demonstrate a cuticle with a reticulate
patterning of flanges and that Nmatoplexus Lyon be used for associations of two
sizes of tubes which cannot be assigned to Prototaxites.
The very resilience of these cuticles and tubular elements suggests that they were
composed of complex polymers at least comparable with lignin and with cutin of
higher vascular plants. It is now necessary to extract each kind of microfossil
separately for chemical analysis. We have begun such a project in Cardiff based on
.Nmatothallus-type cuticles from Dittonian sediments.
The presence of cuticles and spores indicates that the parent plants were
adapted to the terrestrial environment.
As little is known about the morphology of the complete plants, the spatial
organization of tissues and their reproductive characteristics it would be unwise to
fit them into existing taxa. The idea of Lang (1937) of a new higher taxon (based
on the Nematophytales), intermediate between the algae and vascular plants
remains an attractive one, although its erection must await the description of
better preserved, more intact, preferably fertile specimens.
ACKNOWLEDGEMENTS
The material described here was very skilfully and patiently prepared by Mrs E.
C. W. Rogerson whose technical post was financed by a Natural Environment
Research Council grant. I also thank the numerous palaeontological colleagues
with whom I have discussed the affinities of the microfossils and Mrs Val. Rose
who helped prepare the manuscript. The Keeper of Palaeontology British Museum
(Natural History) very kindly allowed access to the Lang collection.
NON-VASCULAR MICROFOSSILS FROM WALES
255
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