in the Coal-Measures, and show that the Labyrinthodonts differed in important particulars from all modern Amphibians, the group which includes our frogs and salamanders. Some of these ancient animals resemble a salamander in shape, while others were serpent-like in form. None of those yet discovered were frog-like, or without a tail, although the restored Labyrinthodont of the text-books is thus represented. All were protected by large pectoral bony plates, and an armor of small scutes on the ventral surface of the body. The walls of their teeth were more or less folded, whence the name Labyrinthodont. The American Amphibians known from osseous remains are all of moderate size, but the footprints attributed to this group indicate animals larger than any of the class yet found in the Old World. The Carboniferous Amphibians were abundant in the swampy tropical forests of that period, and their remains have been found imbedded in the coal then deposited, as well as in hollow stumps of the trees left standing.
The principal genera of this group from American Carboniferous rocks are—Sauropus, known only from footprints, Baphetes, Dendrerpeton, Hylonomus, Hylerpeton, Paniceps, Pelion, Leptophractus, Molgophis, Ptyonius, Amphibamus, Cocytinus, and Ceraterpeton. The last genus occurs also in Europe. Certain of these genera have been considered by some writers to be more nearly related to the lizards, among true reptiles. Some other genera known from fragmentary remains or footprints in this formation have likewise been referred to the true reptiles, but this question can perhaps be settled only by future discoveries.
No Amphibia are known from American Permian strata, but in the Triassic a few characteristic remains have been found. The three genera, Dictyocephalus, Dispelor, and Pariostegus, have been described, but, although apparently all Labyrinthodonts, the remains preserved are not sufficient to add much to our knowledge of the group. The Triassic footprints which have been attributed to Amphibians are still more unsatisfactory, and at present no important conclusions in regard to this class can be based upon them. From the Jurassic and Cretaceous beds of this continent no remains of Amphibians are known. A few only have been found in the Tertiary, and these are all of modern types.
The Amphibia are so nearly allied to the Ganoid fishes that we can hardly doubt their descent from some member of that group. With our present limited knowledge of the extinct forms, however, it would be unprofitable to attempt to trace in detail their probable genealogy.
The authors to whom especial credit is due for our knowledge of American fossil Fishes and Amphibians, are Newberry, Leidy, Cope, Dawson, Agassiz, St. John, Gibbes, Wyman, Redfield, and Emmons, and the principal literature of the subject will be found in their publications.