Page:North American Plesiosaurs- Elasmosaurus, Cimoliasaurus, and Polycotylus.pdf/11

Rh saurian character, but it differs from the propodial of any other elasmosaurian known to me, in having an additional facet for a epipodial at its distal end. There is, also, an additional bone, which is wanting in other species of Elasmosaurus. These characters are, I believe, of generic value, but until the structure of the coracoid is known I leave the species provisionally in this genus. The femur has a length of 370mm, and a width of 218mm.

Thirty-three vertebræ are preserved with the type specimen, but as already stated they have suffered much from distortion, and their exact measurements can not be given. They are all clearly from the posterior part of the neck and the dorsal region. Some of the posterior dorsals are missing, though one of the is preserved. Their characters, so far as they are shown, are clearly elasmosaurian. The ribs are of course single-headed; the spines are broad and not very high; the posterior dorsals are more flattened at their extremities, and their articular rims are sharp, with slight crenulations. The lengths of the centra are given in millimeters, as approximately as the crushed condition will permit, as follows:—

Cervicals: 135, 135, 135, 135, 135, 135, 133, 133, 130, 127, 125, 125, 125, 120.

Dorsals: 115, 115, 115, 112, 110, 110, 100, 95, 90, 90, 90, 90, 90, 90, 90, 90, 90, 85, 80 (sacral).

If this species had similar proportions to those of E. platyurus, its length in life was about fifty feet.

 Williston. Niobrara Cretaceous of Kansas.

Polycotylus ischiadicus Williston, Field Col. Mus. Pub., Geol. Ser., vol. ii, p. 72, pls. x, xxvi, 1903.

This species, based upon the ischia, ilia, caudal and supposed cervical vertebræ, was originally referred provisionally to the genus Polycotylus by myself, though gravely doubting its correct location there. An excellent specimen in the Yale Museum (No. 1130), comprising the front paddle nearly complete, a number of vertebræ, and the nearly complete pectoral girdle, seems to be of the same species. I was at one time inclined to the belief that the specimen represented an undescribed species, notwithstanding the resemblance of the ischia, chiefly because of the differences in the structure of the ilia, and because of the characters of the vertebræ which I had identified as cervical. That all the centra preserved in the Kansas specimen are s seems hardly possible. If any of them are cervicals, the species are undoubtedly distinct. This question, however, I can not decide until I have had an