Page:Synopsis of the Exinct Batrachia and Reptilia of North America. Part 1..pdf/50

46 it would suggest the existence of a fore limb, of comparatively little power, though no remains of such have been found. The acetabulum is smaller than the glenoid cavity ; this point, with the obvious source of propulsive power in the tail, renders it probable that the posterior limbs were the weaker of the two, if any existed. But there is no trace of sacrum nor of any modified diapophyses for support of an ilium.

The ischia are flat, subtriangular bones with a long median line of junction, and communicating anteriorly with the posterior prolongation of the pubic plate. Their postero-exterior margins project well backwards. The pubes are broad plates, whose anterior margins diverge from each other. They are broader than the ischia, and form a broad shallow basin for the support of the viscera. The suture defining these elements is obliterated ; they are continuous, and form a weak inferior keel on the median line. A simple curved ilium has been preserved, for which there appears to be a smooth articular surface on the pubis to which it was attached.

The acetabular portions of these elements are flattened and furnished with convex articular surfaces. The supposed ilia are short curved bones, resembling that of Plesiosaurus latispinus Ow., or of some of the other species of that family. The shank is flattened cylindric, the distal extremity, dilated rounded and flattened. The proximal extremity sub-truncate, or truncate in two or three unequal planes, and with a median pit. It fits well when applied to a concavity on the articular surface of the pubis. The vertebræ above the pelvic arch were furnished with elongate, sub-cylindric diapophyses.

The question as to the presence of posterior limbs remains unsolved. Dr. Turner having made a second careful search, and renewed excavations at the original locality, failed to find any bones which can be assigned to humerus, ulna, radius, carpus or phalanges, or similar elements of the hind limbs. This is the more remarkable, as the pelvic and scapular arches were further completed, and an additional number of ribs obtained. The inferior and lateral regions of the trunk, being then so abundantly discovered, what are we to think of the entire absence of the usually numerous elements of extremities? The glenoid cavity is a rather angular cavity, and both were filled with solid argillaceous matrix. The acetabula are not cup-like, but merely exposures of the marrow, plane extremities of the pubes and ischia, they were covered with thin layers of gypsum; the pieces of the ilia were found imbedded in the mass of matrix which occupied the pelvic arch.

The allied genus Cimoliasaurus Leidy possesses a femur, as described under head of that genus ; it is of shorter and thicker form than in most Plesiosauri.

The skeleton so nearly complete would indicate no violent disturbance of the carcass ; but if there were, it would be an unusual accident that all of the four limbs should have been removed from their sockets, without leaving even fragments.