Page:North American Plesiosaurs- Elasmosaurus, Cimoliasaurus, and Polycotylus.pdf/2

 of his notes have been anticipated by myself or others; others new to me I shall fully acknowledge in each case. The present paper will deal chiefly with this material, that especially belonging to the genus . Other material in the collection will be discussed in later papers, so far as the more important characters are concerned.

The genus Cimoliasaurus has been, and yet is, poorly understood. Lydekker subordinated a dozen or more generic names as, some of which have been accepted as such by later writers. Professor Marsh was inclined, as his notes show, to accept the name Cimoliasaurus in lieu of Elasmosaurus for the species now in the Yale Museum. A brief review, therefore, of the real characters of that genus, as interpreted by the light of considerable material, will not be out of place here.

The type of the genus and species Cimoliasaurus magnus Leidy is a number of and   , , probably from rocks of an  corresponding with the  , and they have been, for the most part, well figured by Leidy in his "Cretaceous Reptiles." With the original specimens he later associated a series of fourteen vertebræ, or rather of vertebræ, from the same locality, and he speaks of such bones being common in the deposits of New Jersey. Leidy, however, sadly misinterpreted the positions of his centra in the vertebral column, nor was Cope much more correct in his interpretation of them. I would interpret figures 13-15 of Plate V of the abovementioned work as of a cervical centrum; figure 16, a more posterior cervical or early ; figures 17-19, a  or -median cervical. Figures 1-3 of Plate VI represent a dorsal centrum; figure 1 is of an dorsal, as is also figure 5; figures 6 and 7 are of a posterior cervical; 8-15, of median cervicals; 16-19, of an anterior cervical.

Leidy's description of the genus  appeared on the page following that of Cimoliasaurus, and was based upon two vertebræ from the Cretaceous of New Jersey (Plate V, figures 1-3) and an anterior caudal vertebra from the same region. Other vertebræ from the Cretaceous Mississippi (figures 10, 11) he afterwards separated as the type of a distinct species, and was probably correct in so doing. Cope long ago showed the similitude of these vertebræ to those of Cimoliasaurus and made the name Discosaurus a synonym, in which Leidy acquiesced.

We may therefore assume that all these vertebræ, save those from Mississippi, pertain not only to Cimoliasaurus, but to