Thus the corals and encrinites remain with scarcely a change in outward form, but of increasing variety, and in countless myriads. The trilobites are nearly extinct, while the annelidæ, which appear not in the devonian system, return to the stage in greater numbers and diversity of structure. The conchiferæ are likewise enlarged in every order; as also the crustaceæ, which are more than quadrupled. Pteropodæ present four genera in the silurian group, decline to one in the devonian, which genus is not found in the carboniferous, but a new one takes its place. The brachiopodæ are again very abundant, as they were in the two former groups. The most characteristic shells of the order and period are the productus, spirifer, terebratula. One genus of heteropoda, the bellerophon, appeared in the silurian rocks, of which there were eleven species. Eight species occur in the devonian system along with a new genus, porcellia. The bellerophon numbers nineteen species in the carboniferous rocks, and the porcellia, which occurs also, contains three. The cephalopods, the most predaceous of their kind, lose generically, while they multiply prodigiously in species during the latter epoch. Thus the goniatites alone amount to fifty-four, the nautili to forty-two, and the orthoceratites, which had declined to twelve in the devonian, swell to thirty-two species in the carboniferous series. But the fishes in this group of rocks exhibit, unquestionably, the largest amount, both in number and form, of new types. Here the sharks and sauroids appear, for the first time, not small, or attenuated in bulk, but vigorous, robust specimens of their kind, strong and expert swimmers, armed with enlarged destructive organs, and every way equipped for maintaining the due proportion of numbers, and the free trade of the ocean. Thus of the order of placoids, there are twenty-eight genera, and ninety-four species; of ganoids there are five genera, and twelve species; and sauroids enumerate thirteen genera, and twenty-four distinct and entirely new specific creations. A specimen of reptilian life has here also been detected; and what is of still greater theoretic importance, in tracing the course of creation, the immediately overlying sandstones have yielded up impressions of the winged tribes that “fly in the open firmament of heaven.” This interesting fact will, in its proper place in the order of superposition, be more fully alluded to.