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THE ANCIENT
LIFE-HISTORY
OF THE EARTH

Chapter 13:

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, Page 171 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.

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 Page 172 with the limestones throughout the Lower Carboniferous series. One of the most interesting of the British Carboniferous forms
Fig. 114.—Transparent slice of Carboniferous Limestone, from Spergen Hill, Indiana, U.S., showing numerous shells of Endothyra (Rotalia), Baiteyi slightly enlarged. (Original.) 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
Fig. 115.—Fusulina cylindrica, Carboniferous Limestone, Russia. Nummulite, precursor of the great and important family of the Tertiary Nummulites.

The sub-kingdom of the Cœlenterates, 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 Page 173 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 Chœtetes, 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, Page 174 from the fact that almost all the varied types of which it is composed disappeared utterly before the close of the Carboniferous
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 Cœtetes 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.) 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 Page 175 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 Palœocoryne, and has been referred to the Hydroid Zoophytes (Corynida). Doubt, however, has been thrown by other observers on the correctness of this reference.]

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,
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.) and Forbesiocrinus. Closely allied to the Crinoids, or forming a kind of transition Page 176 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
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. 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 Page 177 these grooves there seems to have been attached a row of short jointed calcareous filaments or "pinnules."

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
Fig. 119.—Palœchinus 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.) 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 Page 178 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 Archœocidaris. 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 Archœocidaris and Palœchinus; but the characteristic American forms belong principally to Melonites, Oligoporus, and Lepidechinus.

Amongst the Annelides it is only necessary to notice the little spiral tubes of Spirorbis Carbonarius (fig. 120),
Fig. 120.—Spirorbis (Microconchus) Carbonarius, of the natural size, attached to a fossil plant, and magnified. Carboniferous Britain and North America. (After Dawson.) 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.

The Crustaceans of the Carboniferous rocks are numerous, Page 179 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
Fig. 121.—Prestwichia rotundata, a Limuloid Crustacean. Coal-measures, Britain. (After Henry Woodward.) 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 Estheriœ and their allies, which present a curious Page 180 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
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, Palœocaris typus, slightly enlarged—Coal-measures, North America; f, Anthrapalœmon gracilis, of the natural size—Coal-measures, North America. (After De Koninck, M'Coy, Rupert Jones, and Meek and Worthen.) Shrimps (the Macrura), in having a long and well-developed abdomen terminated by an expanded tail-fin. The Palœocaris typus (fig. 122, e) and the Anthrapalœmon 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" Page 181 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.

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
Fig. 123.—Cyclophthalmus senior. A fossil Scorpion from the Coal-measures of Bohemia. 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, Page 182 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
Fig. 124.—Xylobius Sigillariœ, 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.) 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
Fig. 125—Haplophlebium Barnesi, a Carboniferous insect, from the Coal-meastures of Nova Scotia. (After Dawson.) the Devonian period. One of the most remarkable of the latter is a huge May-fly (Haplophlebium Barnesi, fig. 125), with Page 183 netted wings attaining an expanse of fully seven inches, and therefore much exceeding any existing Ephemerid in point of size.

The lower groups of the Mollusca are abundantly represented in the marine strata of the Carboniferous series by Polyzoans
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.)] 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" (Fenestellidœ), some of the characteristic forms of which are here figured (fig. 126). The graceful Page 184 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.

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 Productidœ, 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 Productœ 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 Page 185 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 Productœ, 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
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 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 Page 186 and South America; whilst P. Longispina (fig. 127, b) has a distribution little if at all less wide.

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
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 "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 Ammonitidœ, Page 187 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.

Fig. 129.—Goniatites (Aganides) Fossœ. Carboniferous Limestone.

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 (Cephalaspidœ) Page 188 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 Palœoniscus and Amblypterus (fig. 130), with their small rhomboidal and
Fig. 130.—Amblypterus macropterus. 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.

Page 189 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
Fig. 131.—Teeth of Cochliodus contortus. Carboniferous Limestone, Britain. 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 Page 190 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
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.) 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 Page 191 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:—

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.