THE CARBONIFEROUS PERIOD--Continued.
ANIMAL LIFE OF THE CARBONIFEROUS.
We have seen that there exists a great difference as to the mode
of origin of the Carboniferous sediments, some being purely marine,
whilst others are terrestrial; and others, again, have been formed
in inland swamps and morasses, or in brackish-water lagoons,
creeks, or estuaries. A corresponding difference exists necessarily
in the animal remains of these deposits, and in many regions
this difference is extremely well marked and striking. The great
marine limestones which characterise the lower portion of the
Carboniferous series in Britain, Europe, and the eastern portion
of America, and the calcareous beds which are found high up in
the Carboniferous in the western States of America, may, and
do, often contain the remains of drifted plants; but they are
essentially characterised by marine fossils; and, moreover, they
can be demonstrated by the microscope to be almost wholly composed
of the remains of animals which formerly inhabited the ocean. On
the other hand, the animal remains of the beds accompanying the
coal are typically the remains of air-breathing, terrestrial,
amphibious, or aerial animals, together with those which inhabit
fresh or brackish waters. Marine fossils may be found in the
Coal-measures, but they are invariably confined to special horizons
in the strata, and they indicate temporary depressions of the
land beneath the sea. Whilst the distinction here mentioned is
one which cannot fail to strike the observer, it is convenient
to consider the animal life of the Carboniferous as a whole: and
it is simply necessary, in so doing, to remember that the marine
fossils are in general derived from the inferior portion of the
system; whilst the air-breathing, fresh-water, and brackish-water
forms are almost exclusively derived from the superior portion
of the same.
[Illustration: Fig. 114.--Transparent slice of Carboniferous
Limestone, from Spergen Hill, Indiana, U.S., showing numerous
shells of _Endothyra_ (_Rotalia_), _Baiteyi_ slightly enlarged.
(Original.)]
[Illustration: Fig. 115.--_Fusulina cylindrica_, Carboniferous
Limestone, Russia.]
The Carboniferous _Protozoans_ consist mainly of _Foraminifera_
and _Sponges_. The latter are still very insufficiently known,
but the former are very abundant, and belong to very varied types.
Thin slices of the limestones of the period, when examined by the
microscope, very commonly exhibit the shells of _Foraminifera_
in greater or less plenty. Some limestones, indeed, are made up of
little else than these minute and elegant shells, often belonging
to types, such as the Textularians and Rotalians, differing little
or not at all from those now in existence. This is the case, for
example, with the Carboniferous Limestone of Spergen Hill in
Indiana (fig. 114), which is almost wholly made up of the spiral
shells of a species of _Endothyra_. In the same way, though to a
less extent, the black Carboniferous marbles of Ireland, and
the similar marbles of Yorkshire, the limestones of the west
of England and of Derbyshire, and the great "Scar Limestones" of
the north of England, contain great numbers of Foraminiferous
shells; whilst similar organisms commonly occur in the shale-beds
associated with the limestones throughout the Lower Carboniferous
series. One of the most interesting of the British Carboniferous
forms is the _Saccammina_ of Mr Henry Brady, which is sometimes
present in considerable numbers in the limestones of Northumberland,
Cumberland, and the west of Scotland, and which is conspicuous
for the comparatively large size of its spheroidal or pear-shaped
shell (reaching from an eighth to a fifth of an inch in size).
More widely distributed are the generally spindle-shaped shells
of _Fusulina_ (fig. 115), which occur in vast numbers in the
Carboniferous Limestone of Russia, Armenia, the Southern Alps,
and Spain, similar forms occurring in equal profusion in the
higher limestones which are found in the Coal-measures of the
United States, in Ohio, Illinois, Indiana, Missouri, &c. Mr Henry
Brady, lastly, has shown that we have in the _Nummulina Pristina_
of the Carboniferous Limestone of Namur a genuine _Nummulite_,
precursor of the great and important family of the Tertiary
Nummulites.
[Illustration: Fig. 116--Corals of the Carboniferous Limestone.
a. _Cyathophyllum paracida_, showing young corallites budded
forth from the disc of the old one; a', One of the corallites
of the same, seen in cross-section; b, Fragment of a mass of
_Lithostrotion irregulare_; b', One of the corallites of the
same, divided transversely; c, Portion of the simple cylindrical
coral of _Amplexus coralloides_; c', Transverse section of the
same species; d, _Zaphrentis vermicularis_, showing the depression
or "fossula" on one side of the cup; e, Fragrent of a mass of
_Syringopora ramulosa_; f, Fragment of _Coetetes tumidus_; f',
Portion of the same of the same, enlarged. From the Carboniferous
Limestone of Britain and Belgium. (After Thomson, De Koninck,
Milne-Edwards and Haime, and the Author.)]
The sub-kingdom of the _Coelenterates_, so far as certainly known,
is represented only by _Corals_;[19] but the remains of these are
so abundant in many of the limestones of the Carboniferous formation
as to constitute a feature little or not at all less conspicuous
than that afforded by the Crinoids. As is the case in the preceding
period, the Corals belong, almost exclusively, to the groups of
the _Rugosa_ and _Tabulata_; and there is a general and striking
resemblance and relationship between the coral-fauna of the Devonian
as a whole, and that of the Carboniferous. Nevertheless, there
is an equally decided and striking amount of difference between
these successive faunas, due to the fact that the great majority
of the Carboniferous _species_ are new; whilst some of the most
characteristic Devonian _genera_ have nearly or quite disappeared,
and several new genera now make their appearance for the first
time. Thus, the characteristic Devonian types _Heliophyllum,
Pachyphyllum, Chonophyllum, Acervularia, Spongophyllum, Smithia,
Endophyllum_, and _Cystiphyllum_, have now disappeared; and the
great masses of _Favosites_ which are such a striking feature
in the Devonian limestones, are represented but by one or two
degenerate and puny successors. On the other hand, we meet in
the Carboniferous rocks not only with entirely new genera--such
as _Axophyllum, Lophophyllum_, and _Londsdaleia_--but we have an
enormous expansion of certain types which had just begun to exist
in the preceding period. This is especially well seen in the Case
of the genus _Lithostrotion_ (fig. 116, b), which more than any
other may be considered as the predominant Carboniferous group of
Corals. All the species of _Lithostrotion_ are compound, consisting
either of bundles of loosely-approximated cylindrical stems, or of
similar "coral-lites" closely aggregated together into astræiform
colonies, and rendered polygonal by mutual pressure. This genus
has a historical interest, as having been noticed as early as in
the year 1699 by Edward Lhwyd; and it is geologically important
from its wide distribution in the Carboniferous rocks of both the
Old and New Worlds. Many species are known, and whole beds of
limestone are often found to be composed of little else than
the skeletons of these ancient corals, still standing upright
as they grew. Hardly less characteristic of the Carboniferous
than the above is the great group of simple "cup-corals," of
which _Clisiophyllum_ is the central type. Amongst types which
commenced in the Silurian and Devonian, but which are still well
represented here, may be mentioned _Syringopora_ (fig. 116, e),
with its colonies of delicate cylindrical tubes united at intervals
by cross-bars; _Zaphrentis_ (fig. 116, d), with its cup-shaped
skeleton and the well-marked depression (or "fossula") on one side
of the calice; _Amplexus_ (fig. 116, c), with its cylindrical,
often irregularly swollen coral and short septa; _Cyathophyllum_
(fig. 116, a), sometimes simple, sometimes forming great masses
of star-like corallites; and _Choetetes_, with its branched stems,
and its minute, "tabulate" tubes (fig. 116, f). The above,
together with other and hardly less characteristic forms, combine
to constitute a coral-fauna which is not only in itself perfectly
distinctive, but which is of especial interest, from the fact that
almost all the varied types of which it is composed disappeared
utterly before the close of the Carboniferous period. In the
first marine sediments of a calcareous nature which succeeded to
the Coal-measures (the magnesian limestones of the Permian), the
great group of the _Rugose corals_, which flourished so largely
throughout the Silurian, Devonian, and Carboniferous periods,
is found to have all but disappeared, and it is never again
represented save sporadically and by isolated forms.
[Footnote 19: A singular fossil has been described by Professor
Martin Duncan and Mr Jenkins from the Carboniferous rocks under
the name of _Paloeocoryne_, and has been referred to the Hydroid
Zoophytes (_Corynida_). Doubt, however, has been thrown by other
observers on the correctness of this reference.]
[Illustration: Fig. 117.--_Platycrinus tricontadactylus_, Lower
Carboniferous. The left-hand figure shows the calyx, arms, and
upper part of the stem; and the figure next this shows the surface
of one of the joints of the column. The right-hand figure shows
the proboscis. (After M'Coy.)]
[Illustration: Fig. 118.--A, _Pentremites pyriformis_, side-view
of the body ("calyx"); B, The same viewed from below, showing the
arrangement of the plates; C, Body of _Pentremites conoideus_,
viewed from above. Carboniferous.]
Amongst the _Echinoderms_, by far the most important forms are
the Sea-lilies and the Sea-urchins--the former from their great
abundance, and the latter from their singular structure; but the
little group of the "Pentremites" also requires to be noticed.
The Sea-lilies are so abundant in the Carboniferous rocks, that it
has been proposed to call the earlier portion of the period the
"Age of Crinoids." Vast masses of the limestones of the period
are "crinoidal," being more or less extensively composed of the
broken columns, and detached plates and joints of Sea-lilies,
whilst perfect "heads" may be exceedingly rare and difficult
to procure. In North America the remains of Crinoids are even
more abundant at this horizon than in Britain, and the specimens
found seem to be commonly more perfect. The commonest of the
Carboniferous Crinoids belong to the genera _Cyathocrinus,
Actinocrinus, Platycrinus_, (fig. 117), _Poteriocrinus, Zeacrinus_,
and _Forbesiocrinus_. Closely allied to the Crinoids, or forming
a kind of transition between these and the Cystideans, is the
little group of the "Pentremites," or _Blastoids_ (fig. 118).
This group is first known to have commenced its existence in
the Upper Silurian, and it increased considerably in numbers
in the Devonian; but it was in the seas of the Carboniferous
period that it attained its maximum, and no certain representative
of the family has been detected in any later deposits. The
"Pentremites" resemble the Crinoids in having a cup-shaped body
(fig. 118, A) enclosed by closely-fitting calcareous plates,
and supported on a short stem or "column," composed of numerous
calcareous pieces flexibly articulated together. They differ from
the Crinoids, however, in the fact that the upper surface of
the body does not support the crown of branched feathery "arms,"
which are so characteristic of the latter. On the contrary, the
summit of the cup is closed up in the fashion of a flower-bud,
whence the technical name of _Blastoidea_ applied to the group
(Gr. _blastos_, a bud; _eidos_, form). From the top of the cup
radiate five broad, transversely-striated areas (fig. 118, C),
each with a longitudinal groove down its middle; and along each
side of each of these grooves there seems to have been attached
a row of short jointed calcareous filaments or "pinnules."
[Illustration: Fig. 119.--_Paloechinus ellipticus_, one of the
Carboniferous Sea-urchins. The left-hand figure shows one of the
"ambulacral areas" enlarged, exhibiting the perforated plates.
The right-land figure exhibits a single plate from one of the
"inter-ambulacral areas." (After M'Coy.)]
A few Star-fishes and Brittle-stars are known to occur in the
Carboniferous rocks; but the only other Echinodemls of this period
which need be noticed are the Sea-urchins (_Echinoids_). Detached
plates and spines of these are far from rare in the Carboniferous
deposits; but anything like perfect specimens are exceedingly
scarce. The Carboniferous Sea-urchins agree with those of the
present day in having the body enclosed in a shell formed by
an enormous number of calcareous plates articulated together.
The shell may be regarded as, typically, nearly spherical in
shape, with the mouth in the centre of the base, and the excretory
opening or vent at its summit. In both the ancient forms and the
recent ones, the plates of the shell are arranged in ten zones
which generally radiate from the summit to the centre of the base.
In five of these zones--termed the "ambulacral areas"--the plates
are perforated by minute apertures or "pores," through which
the animal can protrude the little water-tubes ("tube-feet") by
which its locomotion is carried on. In the other five zones--the
so-called "inter-ambulacral areas"--the plates are of larger
size, and are not perforated by any apertures. In all the modern
Sea-urchins each of these ten zones, whether perforate or
imperforate, is composed of two rows of plates; and there are
thus twenty rows of plates in all. In the Palæozoic Sea-urchins,
on the other hand, the "ambulacral areas" are often like those of
recent forms, in consisting of _two_ rows of perforated plates
(fig. 119); but the "inter-ambulacral areas" are always quite
peculiar in consisting each of three, four, five, or more rows
of large imperforate plates, whilst there are sometimes four
or ten rows of plates in the "ambulacral areas" also: so that
there are many more than twenty rows of plates in the entire
shell. Some of the Palæozoic Sea-urchins, also, exhibit a very
peculiar singularity of structure which is only known to exist
in a very few recently-discovered modern forms (viz., _Calveria_
and _Phormosoma_). The plates of the inter-ambulacral areas,
namely, overlap one another in an imbricating manner, so as to
communicate a certain amount of flexibility to the shell; whereas
in the ordinary living forms these plates are firmly articulated
together by their edges, and the shell forms a rigid immovable
box. The Carboniferous Sea-urchins which exhibit this extraordinary
peculiarity belong to the genera _Lepidechinus_ and _Lepidesthes_,
and it seems tolerably certain that a similar flexibility of
the shell existed to a less degree in the much more abundant
genus _Archoeocidaris_. The Carboniferous Sea-urchins, like the
modern ones, possessed movable spines of greater or less length,
articulated to the exterior of the shell; and these structures
are of very common occurrence in a detached condition. The most
abundant genera are _Archoeocidaris_ and _Paloechinus_; but the
characteristic American forms belong principally to _Melonites,
Oligoporus_, and _Lepidechinus_.
[Illustration: Fig. 120.--_Spirorbis (Microconchus) Carbonarius_,
of the natural size, attached to a fossil plant, and magnified.
Carboniferous Britain and North America. (After Dawson.)]
Amongst the _Annelides_ it is only necessary to notice the little
spiral tubes of _Spirorbis Carbonarius_ (fig. 120), which are
commonly found attached to the leaves or stems of the Coal-plants.
This fact shows that though the modern species of _Spirorbis_
are inhabitants of the sea, these old representatives of the
genus must have been capable of living in the brackish waters
of lagoons and estuaries.
[Illustration: Fig. 121.--_Prestwichia rotundata_, a Limuloid
Crustacean. Coal-measures, Britain. (After Henry Woodward.)]
[Illustration: Fig. 122.--Crustaceans of the Carboniferous Rocks.
a, _Phillipsia seminifera_, of the natural size--Mountain Limestone,
Europe; b, One valve of the shell of _Estheria tenella_, of the
natural size and enlarged--Coal-measures, Europe; c, Bivalved
shell of _Entomoconchus Scouleri_, of the natural size--Mountain
Limestone, Europe; d, _Dithyrocaris Scouleri_, reduced in
size--Mountain Limestone, Ireland; e, _Paloeocaris typus_, slightly
enlarged--Coal-measures, North America; f, _Anthrapaloemon gracilis_,
of the natural size--Coal-measures, North America. (After De
Koninck, M'Coy, Rupert Jones, and Meek and Worthen.)]
The _Crustaceans_ of the Carboniferous rocks are numerous, and
belong partly to structural types with which we are already familiar,
and partly to higher groups which come into existence here for the
first time. The gigantic _Eurypterids_ of the Upper Silurian and
Devonian are but feebly represented, and make their final exit
here from the scene of life. Their place, however, is taken by
peculiar forms belonging to the allied group of the _Xiphosura_,
represented at the present day by the King-crabs or "Horse-shoe
Crabs" (_Limulus_). Characteristic forms of this group appear
in the Coal-measures both of Europe and America; and though
constituting three distinct genera (_Prestwichia, Belinurus_,
and _Euproöps_), they are all nearly related to one another. The
best known of them, perhaps, is the _Prestwichia rotundala_ of
Coalbrookdale, here figured (fig. 121). The ancient and formerly
powerful order of the _Trilobites_ also undergoes its final
extinction here, not surviving the deposition of the Carboniferous
Limestone series in Europe, but extending its range in America
into the Coal-measures. All the known Carboniferous forms are
small in size and degraded in point of structure, and they are
referable to but three genera (_Phillipsia, Griffithides_, and
_Brachymetopus_), belonging to a single family. The _Phillipsia
seminifera_ here figured (fig. 122, a) is a characteristic species
in the Old World. The Water-fleas (_Ostracoaa_) are extremely
abundant in the Carboniferous rocks, whole strata being often
made up of little else than the little bivalved shells of these
Crustaceans. Many of them are extremely small, averaging about
the size of a millet-seed; but a few forms, such as _Entomoconchus
Scouleni_ (fig. 122, c), may attain a length of from one to
three quarters of an inch. The old group of the _Phyllopods_
is is likewise still represented in some abundance, partly by
tailed forms of a shrimp-like appearance, such as _Dithyrocaris_
(fig. 122, d), and partly by the curious striated _Estherioe_
and their allies, which present a curious resemblance to the
true Bivalve Molluscs (fig. 122, b). Lastly, we meet for the
first time in the Carboniferous rocks with the remains of the
highest of all the groups of _Crustaceans_--namely, the so-called
"Decapods," in which there are five pairs of walking-limbs, and
the hinder end of the body ("abdomen") is composed of separate
rings, whilst the anterior end is covered by a head-shield or
"carapace." All the Carboniferous Decapods hitherto discovered
resemble the existing Lobsters, Prawns, and Shrimps (the _Macrura_),
in having a long and well-developed abdomen terminated by an
expanded tail-fin. The _Paloeocaris typus_ (fig. 122, e) and the
_Anthrapaloemon gracilis_ (fig. 122, f), from the Coal-measures
of Illinois, are two of the best understood and most perfectly
preserved of the few known representatives of the "Long-tailed"
Decapods in the Carboniferous series. The group of the Crabs
or "Short-tailed" Decapods (_Brachyura_), in which the abdomen
is short, not terminated by a tail-fin, and tucked away out of
sight beneath the body, is at present not known to be represented
at all in the Carboniferous deposits.
[Illustration: Fig. 123.--_Cyclophthalmus senior_. A fossil Scorpion
from the Coal-measures of Bohemia.]
[Illustration: Fig. 124.--_Xylobius Sigillarioe_, a Carboniferous
Myriapod. a, A specimen, of the natural size; b, Anterior
portion of the same, enlarged; c, Posterior portion, enlarged.
From the Coal-measures of Nova Scotia. (After Dawson.)]
[Illustration: Fig. 125--_Haplophlebium Barnesi_, a Carboniferous
insect, from the Coal-meastures of Nova Scotia. (After Dawson.)]
In addition to the water-inhabiting group of the Crustaceans, we
find the articulate animals to be represented by members belonging
to the air-breathing classes of the _Arachnida, Myriapoda_, and
_Insecta_. The remains of these, as might have been expected, are
not known to occur in the marine limestones of the Carboniferous
series, but are exclusively found in beds associated with the Coal,
which have been deposited in lagoons, estuaries, or marshes, in
the immediate vicinity of the land, and which actually represent
an old land-surface. The _Arachnids_ are at present the oldest
known of their class, and are represented both by true Spiders
and Scorpions. Remains of the latter (fig. 123) have been found
both in the Old and New Worlds, and indicate the existence in
the Carboniferous period of Scorpions differing but very little
from existing forms. The group of the _Myriapoda_, including
the recent Centipedes and Galley-worms, is likewise represented
in the Carboniferous strata, but by forms in many respects very
unlike any that are known to exist at the present day. The most
interesting of these were obtained by Principal Dawson, along
with the bones of Amphibians and the shells of Land-snails, in
the sediment filling the hollow trunks of _Sigillaria_, and they
belong to the genera _Xylobius_ (fig. 124) and Archiulus. Lastly,
the true _insects_ are represented by various forms of Beetles
(_Coleoptera_), _Orthoptera_ (such as Cockroaches), and
_Neuropterous_ insects resembling those which we have seen to
have existed towards the close of the Devonian period. One of the
most remarkable of the latter is a huge May-fly (_Haplophlebium
Barnesi_, fig. 125), with netted wings attaining an expanse of
fully seven inches, and therefore much exceeding any existing
Ephemerid in point of size.
[Illustration: Fig. 126.--Carboniferous _Polyzoa_. a, Fragment
of _Polypora dendroides_, of the natural size, Ireland; a' Small
portion of the same, enlarged to show the cells; b, Glauconome
pulcherrima_, a fragment, of the natural size, Ireland; b',
Portion of the same, enlarged; c, The central screw-like axis
of _Archimedes Wortheni_, of the natural size--Carboniferous,
America; c', Portion of the exterior of the frond of the same,
enlarged; c'', Portion of the interior of the frond of the
same showing the mouths of the cells, enlarged. (After M'Coy and
Hall.)]
The lower groups of the _Mollusca_ are abundantly represented
in the marine strata of the Carboniferous series by _Polyzoans_
and _Brachiopods_. Amongst the former, although a variety of other
types are known, the majority still belong to the old group of
the "Lace-corals" (_Fenestellidoe_), some of the characteristic
forms of which are here figured (fig. 126). The graceful netted
fronds of _Fenestella, Retepora_, and _Polypora_ (fig. 126, a)
are highly characteristic, as are the slender toothed branches
of _Glauconome_ (fig. 126, b). A more singular form, however,
is the curious _Archimedes_ (fig. 126, c), which is so
characteristic of the Carboniferous formation of North America.
In this remarkable type, the colony consists of a succession of
funnel-shaped fronds, essentially similar to _Fenestella_ in
their structure, springing in a continuous spiral from a strong
screw-like vertical axis. The outside of the fronds is simply
striated; but the branches exhibit on the interior the mouths of
the little cells in which the semi-independent beings composing
the colony originally lived.
[Illustration: Fig. 127.--Carboniferous _Braciopoda. a, _Producta
semireticulata_, showing the slightly concave dorsal valve; a'
Side view of the same, showing the convex ventral valve; b,
_Producta longispina_; c, _Orthis resupinata_; d, _Terebratula
hastata_; e, _Athyris subtilita_; f, _Chonetes Hardrensis_; g,
_Rhynchonella pleurodon_; h, _Spirifera trigonalis_. Most of
these forms are widely distributed in the Carboniferous Limestone
of Britain, Europe, America, &c. All the figures are of the natural
size. (After Davidson, De Koninck, and Meek.)]
The _Brachiopods_ are extremely abundant, and for the most part
belong to types which are exclusively or principally Palæozoic
in their range. The old genera _Strophomena, Orthis_ (fig. 127,
c), _Athyris_ (fig. 127, e), _Rhynchonella_ (fig. 127, g),
and _Spirifera_ (fig. 127, h), are still well represented--the
latter, in particular, existing under numerous specific forms,
conspicuous by their abundance and sometimes by their size. Along
with these ancient groups, we have representatives--for the first
time in any plenty--of the great genus _Terebratula_ (fig. 127,
d), which underwent a great expansion during later periods,
and still exists at the present day. The most characteristic
Carboniferous Brachiopods, however, belong to the family of the
_Productidoe_, of which the principal genus is _Producta_ itself.
This family commenced its existence in the Upper Silurian with
the genus _Chonetes_, distinguished by its spinose hinge-margin.
This genus lived through the Devonian, and flourished in the
Carboniferous (fig. 127, f). The genus _Producta_ itself,
represented in the Devonian by the nearly allied _Productella_,
appeared first in the Carboniferous, at any rate, in force, and
survived into the Permian; but no member of this extensive family
has yet been shown to have over-lived the Palæozoic period. The
_Productoe_ of the Carboniferous are not only exceedingly abundant,
but they have in many instances a most extensive geographical range,
and some species attain what may fairly be considered-gigantic
dimensions. The shell (fig. 127, a and b) is generally more
or less semicircular, with a straight hinge-margin, and having
its lateral angles produced into larger or smaller ears (hence
its generic name--"_cochlea producta_"). One valve (the ventral)
is usually strongly convex, whilst the other (the dorsal) is flat
or concave, the surface of both being adorned with radiating
ribs, and with hollow tubular spines, often of great length.
The valves are not locked together by teeth, and there is no
sign in the fully-grown shell of an opening in or between the
valves for the emission of a muscular stalk for the attachment
of the shell to foreign objects. It is probable, therefore, that
the _Productoe_, unlike the ordinary Lamp-shells, lived an
independent existence, their long spines apparently serving to
anchor them firmly in the mud or ooze of the sea-bottom; but Mr
Robert Etheridge, jun.; has recently shown that in one species
the spines were actually employed as organs of adhesion, whereby
the shell was permanently attached to some extraneous object,
such as the stem of a Crinoid. The two species here figured are
interesting for their extraordinarily extensive geographical
range--_Producta semireticulata_ (fig. 127, a) being found
in the Carboniferous rocks of Britain, the continent of Europe,
Central Asia, China, India, Australia, Spitzbergen, and North
and South America; whilst _P. Longispina_ (fig. 127, b) has
a distribution little if at all less wide.
[Illustration: Fig. 128.--_Pupa (Dendropupa) vetusta_, a
Carboniferous Land-snail from the Coal-measures of Nova Scotia.
a, The shell, of the natural size; b, The same, magnified;
c, Apex of the shell, enlarged; d, Portion of the surface,
enlarged. (After Dawson.)]
The higher _Mollusca_ are abundantly represented in the Carboniferous
rocks by Bivalves (_Lamellibranchs_), Univalves (_Gasteropoda_),
Winged-snails (_Pteropoda_), and _Cephalopods_. Amongst the Bivalves
we may note the great abundance of Scallops (_Aviculopecten_ and
other allied forms), together with numerous other types--some of
ancient origin, others represented here for the first time. Amongst
the Gasteropods, we find the characteristically Palæozoic genera
_Macrocheilus_ and _Loxonema_, the almost exclusively Palæozoic
_Euomphalus_, and the persistent, genus _Pleurotomaria_; whilst
the free-swimming Univalves (_Heteropoda_)are represented by
_Bellerophon_ and _Porcellia_, and the _Pteropoda_ by the old
genus _Conularia_. With regard to the Carboniferous Univalves,
it is also of interest to note here the first appearance of true
air-breathing or terrestrial Molluscs, as discovered by Dawson
and Bradley in the Coal-measures of Nova Scotia and Illinois. Some
of these (_Conulus priscus_) are true Land-snails, resembling the
existing _Zonites_; whilst others (_Pupa vetusta_, fig. 128) appear
to be generically inseparable from the "Chrysalis-shells" (_Pupa_)
of the present day. All the known forms--three in number--are of
small size, and appear to have been local in their distribution
or in their preservation. More important, however, than any of
the preceding, are the _Cephalopoda_, represented, as before,
exclusively by the chambered shells of the Tetrabranchiates.
The older and simpler type of these, with simple plain septa,
and mostly a central siphuncle, is represented by the straight
conical shells of the ancient genus Orthoceras, and the bow-shaped
shells of the equally ancient _Cyrtoceras_--some of the former
attaining a great size. The spirally-curved discoidal shells
of the persistent genus _Nautilus_ are also not unknown, and
some of these likewise exhibit very considerable dimensions.
Lastly, the more complex family of the _Ammonitidoe_, with lobed
or angulated septa, and a dorsally-placed siphuncle (situated on
the convex side of the curved shells), now for the first time
commences to acquire a considerable prominence. The principal
representative of this group is the genus _Goniatites_ (fig.
129), which commenced its existence in the Upper Silurian, is well
represented in the Devonian, and attains its maximum here. In this
genus, the shell is spirally curved, the septa are strongly lobed
or angulated, though not elaborately frilled as in the Ammonites,
and the siphuncle is dorsal. In addition to _Goniatites_, the
shells of true _Ammonites_, so characteristic of the Secondary
period, have been described by Dr Waagen as occurring in the
Carboniferous rocks of India.
[Illustration: Fig. 129.--_Goniatites (Aganides) Fossoe_.
Carboniferous Limestone.]
[Illustration: Fig. 130.--_Amblypterus macropterus_. Carboniferous.]
Coming finally to the _Vertebrata_, we have in the first place
to very briefly consider the Carboniferous _fishes_. These are
numerous; but, with the exception of the still dubious "Conodonts,"
belong wholly to the groups of the _Ganoids_ and the _Placoids_
(including under the former head remains which perhaps are truly
referable to the group of the _Dipnoi_ or Mud-fishes). Amongst the
_Ganoids_, the singular buckler-headed fishes of the Upper Silurian
and Devonian (_Cephalaspidoe_) have apparently disappeared; and
the principal types of the Carboniferous belong to the groups
respectively represented at the present day by the Gar pike
(_Lepidosteus_) of the North American lakes, and the _Polypterus_
of the rivers of Africa. Of the former, the genera _Paloeoniscus_
and _Amblypterus_ (fig. 130), with their small rhomboidal and
enamelled scales, and their strongly unsymmetrical tails, are
perhaps the most abundant. Of the latter, the most important are
species belonging to the genera _Megalichthys_ and _Rhizodus_,
comprising large fishes, with rhomboidal scales, unsymmetrical
("heterocercal") tails, and powerful conical teeth. These fishes
are sometimes said to be "sauroid," from their presenting some
Reptilian features in their organisation, and they must have been
the scourges of the Carboniferous seas. The remains of _Placoid_
fishes in the Carboniferous strata are very numerous, but consist
wholly of teeth and fin-spines, referable to forms more or less
closely allied to our existing Port Jackson Sharks, Dog-fishes,
and Rays. The teeth are of very various shapes and sizes,--some
with sharp, cutting edges (_Petalodus, Cladodus_, &c.); others in
the form of broad crushing plates, adapted, like the teeth of the
existing Port Jackson Shark (_Cestracion Philippi_), for breaking
down the hard shells of Molluscs and Crustaceans. Amongst the many
kinds of these latter, the teeth of _Psammodus_ and _Cochliodus_
(fig. 131) may be mentioned as specially characteristic. The
fin-spines are mostly similar to those so common in the Devonian
deposits, consisting of hollow defensive spines implanted in
front of the pectoral or other fins, usually slightly curved,
often superficially ribbed or sculptured, and not uncommonly
serrated or toothed. The genera _Ctenacanthus, Gyracanthus,
Homacanthus_, &c., have been founded for the reception of these
defensive weapons, some of which indicate fishes of great size
and predaceous habits.
[Illustration: Fig. 131.--Teeth of _Cochliodus contortus_.
Carboniferous Limestone, Britain.]
[Illustration: Fig. 132.--a, Upper surface of the skull of
_Anthracosaurus Russelli_, one-sixth of the natural size: b,
Part of one of the teeth cut across, and highly magnified to
show the characteristic labyrinthine structure; c, One of the
integumentary shields or scales, one-half of the natural size.
Coal-measures, Northumberland. (After Atthey.)]
In the Devonian rocks we meet with no other remains of
Vertebrated animals save fishes only; but the Carboniferous
deposits have yielded remains of the higher group
of the _Amphibians_. This class, comprising our existing
Frogs, Toads, and Newts, stands to some extent in a position midway
between the class of the fishes and that of the true
reptiles, being distinguished from the latter by the fact
that its members invariably possess gills in their early
condition, if not throughout life; whilst they are separated from
the former by always possessing true lungs when adult, and
by the fact that the limbs (when present at all) are never in
the form of fins. The Amphibians, therefore, are all
water-breathers when young, and have respiratory organs adapted
for an aquatic mode of life; whereas, when grown up, they
develop lungs, and with these the capacity for breathing air
directly. Some of them, like the Frogs and Newts, lose their
gills altogether on attaining the adult condition; but others,
such as the living _Proteus_ and _Menobranchus_, retain
their gills even after acquiring their lungs, and are thus fitted
indifferently for an aquatic or terrestrial existence. The name of
"Amphibia," though applied to the whole class, is thus not
precisely appropriate except to these last-mentioned forms
(Gr. _amphi_, both; _bios_, life). The Amphibians also
differ amongst themselves according as to whether they keep
permanently the long tail which they all possess when young (as
do the Newts and Salamanders), or lose this appendage when
grown up (as do the Frogs and Toads). Most of them have
naked skins, but a few living and many extinct forms have
hard structures in the shape of scales developed in the integument.
All of them have well-ossified skeletons, though some
fossil types are partially deficient in this respect; and all of
them which possess limbs at all have these appendages supported
by bones essentially similar to those found in the limbs
of the higher Vertebrates. All the Carboniferous Amphibians
belong to a group which has now wholly passed away--namely,
that of the _Labyrinthodonts_. In the marine strata which
form the base of the Carboniferous series these creatures have only
been recognised by their curious hand-shaped footprints, similar
in character to those which occur in the Triassic rocks, and which
will be subsequently spoken of under the name of _Cheirotherium_.
In the Coal-measures of Britain, the continent of Europe, and
North America, however, many bones of these animals have
been found, and we are now tolerably well acquainted with a
considerable number of forms. All of them seem to have
belonged to the division of Amphibians in which the long tail
of the young is permanently retained; and there is evidence
that some of them kept the gills also throughout life. The skull
is of the characteristic Amphibian type (fig. 132, a), with
two occipital condyles, and having its surface singularly pitted
and sculptured; and the vertebræ are hollowed out at both
ends. The lower surface of the body was defended by an armour
of singular integumentary shields or scales (fig. 132, c);
and an extremely characteristic feature (from which the entire
group derives its name) is, that the walls of the teeth are deeply
folded, so as to give rise to an extraordinary "labyrinthine"
pattern when they are cut across (fig. 132, b). Many of the
Carboniferous Labyrinthodonts are of no great size, some of
them very small, but others attain comparatively gigantic
dimensions, though all fall short in this respect of the huge
examples of this group which occur in the Trias. One of the
largest, and at the same time most characteristic, forms of the
Carboniferous series, is the genus _Anthracosaurus_, the
skull of which is here figured.
No remains of true Reptiles, Birds, or Quadrupeds have as yet
been certainly detected in the Carboniferous deposits in any part
of the world. It should, however, be mentioned, that Professor
Marsh, one of the highest authorities on the subject, has described
from the Coal-formation of Nova Scotia certain vertebræ which
he believes to have belonged to a marine reptile (_Eosaurus
Acadianus_), allied to the great _Ichthyosauri_ of the Lias. Up to
this time no confirmation of this determination has been obtained
by the discovery of other and more unquestionable remains, and
it therefore remains doubtful whether these bones of _Eosaurus_
may not really belong to large Labyrinthodonts.
LITERATURE.
The following list contains some of the more important of the
original sources of information to which the student of Carboniferous
rocks and fossils may refer:--
(1) 'Geology of Yorkshire,' vol. ii.; 'The Mountain Limestone
District.' John Phillips.
(2) 'Siluria.' Sir Roderick Murchison.
(3) 'Memoirs of the Geological Survey of Great Britain and Ireland.'
(4) 'Geological Report on Londonderry,' &c. Portlock.
(5) 'Acadian Geology.' Dawson.
(6) 'Geology of Iowa,' vol. i. James Hall.
(7) 'Reports of the Geological Survey of Illinois' (Geology and
Palæontology). Meek, Worthen, &c.
(8) 'Reports of the Geological Survey of Ohio' (Geology and
Palæontology). Newberry, Cope, Meek, Hall, &c.
(9) 'Description des Animaux fossiles qui se trouvent dans le
Terrain Carbonifère de la Belgique,' 1843; with subsequent
monographs on the genera _Productus_ and _Chonetes_,
on _Crinoids_, on _Corals_, &c. De Koninck.
(10) 'Synopsis of the Carboniferous Fossils of Ireland.' M'Coy.
(11) 'British Palæozoic Fossils.' M'Coy.
(12) 'Figures of Characteristic British Fossils.' Baily.
(13) 'Catalogue of British Fossils.' Morris.
(14) 'Monograph of the Carboniferous Brachiopoda of Britain'
(Palæontographical Society). Davidson.
(15) 'Monograph of the British Carboniferous Corals'
(Palæontographical Society). Milne-Edwards and Haime.
(16) 'Monograph of the Carboniferous Bivalve Entomostraca of
Britain' (Palæontographical Society). Rupert Jones, Kirkby, and
George S. Brady.
(17) 'Monograph of the Carboniferous Foraminifera of Britain'
(Palæontographical Society). H. B. Brady.
(18) "On the Carboniferous Fossils of the West of Scotland"--'Trans.
Geol. Soc.,' of Glasgow, vol. iii., Supplement. Young and
Armstrong.
(19) 'Poissons Fossiles.' Agassiz.
(20) "Report on the Labyrinthodonts of the Coal-measures"--'British
Association Report,' 1873. L. C. Miall.
(21) 'Introduction to the Study of Palæontological Botany.' John
Hutton Balfour.
(22) 'Traité de Paléontologie Végétale.' Schimper.
(23) 'Fossil Flora.' Lindley and Hutton.
(24) 'Histoire des Végétaux Fossiles.' Brongniart.
(25) 'On Calamites and Calamodendron' (Monographs of the
Palæontographical Society). Binney.
(26) 'On the Structure of Fossil Plants found in the Carboniferous
Strata' (Palæontographical Society). Binney.
Also numerous memoirs by Huxley, Davidson, Martin Duncan, Professor
Young, John Young, R. Etheridge, jun., Baily, Carruthers, Dawson,
Binney, Williamson, Hooker, Jukes, Geikie, Rupert Jones, Salter,
and many other British and foreign observers.