The ilium (62), like the scapula, is expanded at its articular or femoral end. It is less long and slender ; one border is straight, the other concave, by the expansion toward that border of the femoral end. Two shorter bones on each side complete the pelvis below. One is of a simple form, straight, thicker in proportion to its length than in the ilium : it may be ischium.
The other bone is shown, with its fellow, in t. xiii., fig. 6, and xviii., figs. 8 and 9, of Von Meyer's treatise. That author compares the pair of bones to the Aptychus in shape ; they may be the pubic bones. On this hypothesis, they are restored to their true position at 64 (pubis) in fig. 65. The femur (6s) is slightly expanded, and truncate at both ends ; it is not longer than the ilium. The tibia (66) and fibula are separate bones, like those of the fore-arm ; the margins, which are turned toward each other, are most concave. They are rather more than half the length of the femur.
The foot-bones are separated by a fibro-cartilaginous tarsal mass (68) from those of the leg. The form of the phalanges, expanded and truncate at both ends, bespeaks their simple ligamentous joints, and that they supported, like the fore-limb, a fin or limb adapted simply for swimming. The argument for the saurian affinities of Archegosaurus, based by V. Meyer on the short fore-limbs of Mystriosaurus, already invalidated by the difference of structure, is controverted by the fact, that the hind limbs of Archegosaurus, like those of the Perenni branchs, are not only as simple in structure, but also as short, as the fore-limbs.
Genus DENDRERPETON.-111 1852 Sir Charles Lyell and Mr. Dawson, in the course of their investigations of the coal strata of Nova Scotia, remarkable for the erect fossil trees in certain parts, discovered in the hollow of the trunk of one of these trees (Sigillaria, 2 feet in diameter), which was wholly con verted into coal, some small bones, which Professor Wyman of Boston surmised to have belonged to a batrachian reptile.
By the professor's advice they were brought to England and submitted to the writer, who has described and figured them* as batrachian, under the name Dendrerpeton Acculianum, and with close affinities, from the plicated structure of the teeth, the sculpturing of some broad cranial plates, and the structure and proportions of certain limb-bones, to the genus Arehego saurus. The subsequent discovery of carinate scales with bones of the Dendrerpeton adds to the probability of its apper taining to the Ganocephalous order.
Genus RAXICEPS.—In about the centre of the great car boniferous basin of Ohio, United States, at the mouth of the " yellow creek," is a seam of coal 8 feet in thickness, the lower four inches of which is " cannel coal." In this has been found the skull, part of the vertebral column, scapular arch, and fore limbs of a reptile referred by Professor Wymant to the batra chian sub-class, under the name of Raniceps. Two closely allied fossils, also referred to Batrachia, have been found in the same formation and locality.