Of the few bones of the extremities which have come under the writer's inspection, one presents all the characteristics of the corresponding part of the humerus of a toad or frog, viz., the convex, somewhat transversely extended articular end, the internal longitudinal depression, and the well-developed del toid ridge. The length of the fiyigment is two inches, and the breadth is thirteen lines. The ridges are moderately thick and compact, with a central medullary cavity. In its structure, as well as in its general form, the present bone agrees with the batrachian, and differs from the crocodilian type.
As the fragment of the ilium was discovered in the same block as the two fragments of the cranium and the portion of the lower jaws, it is probable that they may have belonged to the same animal ; and if so, as the portions of the head corres pond in size with those of the head of a crocodile six or seven feet in length, but the acetabular cavity with that of a crocodile twenty-five feet in length, then the hinder extremities of the Labyrinthodon must have been of disproportionate magnitude compared with those of existing Saurians, but of approximate magnitude with some of the living anourous Batrachians. That such a reptile, of a size equal to that of the species whose remains have just been described, existed at the period of the formation of the new red sandstone, is abundantly mani fested by the remains of those singular impressions to which the term Cheirotherium has been applied. Other impressions, as those of the Cheirotherium Hercules, correspond in size with the remains of the Labyrinthodon salamandroides, which have been discovered at Guy's Cliff. The head of a femur from the same quarry in which the ilium was found is shown to corres pond in size with the articulate cavity of the acetabulurn. The two toe-bones, or terminal phalanges, resemble those of Batrachians in presenting no trace of a nail, and from their size they may be referred to the hind feet of the L. pachygnatkus.
An entire skull of the largest species discovered in the new red sandstones of Wurtemberg ; a lower jaw of the same species found in the same formation in Warwickshire ; some vertebra, and a few fragments of bones of the limbs, have served, with the indications of size and shape of the trunk of the animal yielded by the series of consecutive footprints, as the basis of the restoration of the Labyrinthodon salaman droides, at the Crystal Palace. It is to be understood, how ever, that, with the exception of the head, the form of the animal is necessarily more or less conjectural.
Labyrinthodon scntulatus.—The remains to which this specific designation has been applied compose a closely and irregularly aggregated group of bones imbedded in sandstone, and manifestly belonging to the same skeleton ; they consist of four vertebra, portions of ribs, a humerus, a femur, two tibiae, one end of a large flat bone, and several small osseous externally sculptured dermal scutes, which show that the crocodilian nature of a fossil reptile is not determinable by scutes only. The mass was discovered in the new red sand stone at Leamington, and was transmitted to the writer in the summer of 1840.
The vertebra present biconcave articular surfaces similar to those of the other species. In two of them the surfaces slope in a parallel direction obliquely from the axis of the vertebrae, as in the dorsal vertebra of the frog, indicating a habitual inflexion of the spine, analogous to that in the humped back of the frog. The neurapophyses are anchylosed to the vertebral body. The spinous process rises from the whole length of the middle line of the neurapophysial arch, and its chief peculiarity is the expansion of its elongated summit into a horizontally-flattened plate, sculptured irregularly on the upper surface. A similar flattening of the summit of the elongated spine is exhibited in the large atlas of the toad. The body of the vertebra agrees with that of the L. leptog nathus. The humerus is an inch long, regularly convex at the proximal extremity, and expanded at both extremities, but contracted in the middle. A portion of a somewhat shorter and flatter bone is bent at a subacute angle with the distal extremity, and resembles most nearly the anchylosed radius and ulna of the Batrachia.