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shells of this group are not by any means strictly confined in locality or limited in its range, and, with the exception of the terebratula, they are perhaps the most widely distributed of the fossils of the first epoch. Several species pass likewise into the lower beds of the middle epoch; and it is not unlikely that some of the species referred to terebratula, and now living, may ultimately be recognized as spirifers. The species of terebratula of the mountain limestone
(fig. 35) are not very strongly marked, and some of them are capable of misleading the young fossilist by their great resemblance to shells of a much
newer period. The species figured admits of a singular extent of variety of form.
There are many other bivalve shells of the carboniferous limestone, and some of them are of considerable interest, but I cannot here venture upon any detailed account of them. On the whole, there is a manifest approach to the existing type, although many genera at that time existed, all the species of which have since vanished, and a much greater number of new genera have been since introduced.
Of univalve shells there are several which seem to have been either chiefly or entirely confined to the rocks of the carboniferous period. The name Bellerophon (fig. 36, 37) has been given to one genus
* Bellerophon, a Greek name of a person supposed to have lived in the heroic age. As applied to the fossil, this name is entirely fanciful.
of doubtful affinity, which has been referred in succession to various groups of Mollusca, and even to
the Pteropoda, known to occur in the silurian rocks. The great thickness of the shell, its structure and mode of growth, and the kind of shells associated with it, render it more likely, perhaps, that the animal belonged to the Gasteropoda, and was not far removed from the limpet.*
The Cirrus, a flat shell, composed of a number of whorls, and often
size, seems to have inhabited the same muddy bottoms near shore; and the Euomphalus (fig. 39) probably resembled it in habit.
* De Koninck, Animaux Fossiles de la Belgique, p. 334.
+ Cirrus, a curl; so called from the form of the shell.
Euomphalus,- -Ev (eu), elegant; oupaλos (omphalus), a boss: so called
from the well-marked and distinct proportions of the shell.
But the cephalopodous inhabitants of the seas during the carboniferous period were still the most important and the most numerous of the molluscous animals; and they included not only the straight shells of orthoceratites, but a large number of spirally twisted species, bearing a somewhat different relation to the nautilus. The most important are called Goniatites* (fig. 40). The nature of the difference here exhibited, and its influence on the habits of the animal, will be considered in a future chapter, when speaking of the Ammonites, fossils of a yet newer period.
It has been already mentioned that the fishes, which, during the devonian period were for the most part of small size, and could not have been extremely formidable or powerful, were gradually advancing in development towards the latter part of the period, and that several new forms, of strange aspect and gigantic size, were then introduced. These seem to have attained their maximum of size and strength during the carboniferous epoch.
Two great natural families of fishes, one of them entirely, and the other almost extinct, seem to have occupied at this time the place of the great marine reptiles which succeeded and displaced them. These two families are nearly allied to each other, and pre
* Goniatites, yoμoç (gonos), an angle; from the angular markings made by the intersection of the walls of the chambers and the outer shell. (See cut.)
sent many remarkable and close analogies to the true saurians or reptiles, and for this reason the one first determined was named Sauroid.* The sauroid or reptilian fishes, although met with throughout in the rocks of the secondary epoch, and often very abundant, nowhere attain so great a magnitude, or offer such perfect types of their development, as in the earlier seas, whose inhabitants we are now considering.
So intimate is the resemblance, and so nearly perfect the passage between fishes and reptiles through these sauroid fishes, that very little is wanting to complete our knowledge of the numerous extinct forms, in spite of the rarity of existing species with which to compare them. It will, however, be better to confine our attention chiefly to the one or two genera most remarkable and most characteristic, in order to obtain an idea of the peculiarities which distinguished the ancient fishes from their living type.
The Megalichthys‡ (fig. 41), as its name imports, was an animal of large size, and seems also to have been of great strength. Its head was large, and the gape of the jaws enormous; the jaws themselves powerful, and provided with a range of most formidable teeth, of which some of enormous size projected far beyond the rest, as is the case with the crocodile. The
Lavpoc (sauros), a lizard; ɛdwv (eidon), resembling: from the strong saurian or reptilian analogies exhibited, chiefly in the teeth.
The existing sauroid fishes consist of seven species only, five of them belonging to the genus Lepidosteus, or bony pike, which are sufficiently common in the great American rivers; and two species of Polypterus, one from the Nile, and the other from the Niger. The scale of one species of Lepidosteus is figured in page 61, fig. 20.
Meyaλn, (megale), great; ix0vç (ichthys), a fish.
dimensions to which the animal must have attained may be imagined, when it is known that these teeth have been found measuring four inches in length,
JAW AND TEETH OF GIGANTIC SAUROID FISH.
and nearly two inches broad at the base, a size rarely if ever met with even in the largest reptiles. The body, covered with scales of corresponding magnitude (sometimes five inches in diameter), was well shaped for swimming, being formed upon a robust bony skeleton, and provided with an extremely large and powerful tail, enabling it to advance with extreme rapidity. It must have been eminently carnivorous, and capable of pursuing and taking almost any living creature among its contemporaries.*
The Holoptychius,† a genus nearly allied in many respects to the sauroids, seems to have differed from that family in some important points of structure. The specimen best known of this fish is about thirty inches long without the tail, and exhibits the most
* Although unquestionably a fish of large size, and, compared with other fishes of the ganoid order, truly gigantic, it was by no means so with reference to many existing tribes. The ganoid fishes, however, were generally small or of moderate dimensions.
+ 'Olos (holos), entire, complete; and πтʊɣn (płyche), a wrinkle, or fold: the fish's scales being entirely covered with wrinkled markings.