1894.] J-^«^ [Cope. 



On the Structure of the Skullin the Plesiosaurian Reptilia, and on Iwo New 

 Species from the Uj)per Cretaceous. 



By E. B. Cope. 



(Read before the American Philosophical Society, February S, IS94.) 



Prof. S. W. Williston has described in the Proceedings of the Kansas 

 Academy of Science for 1890, the skull and part of the skeleton of a 

 Plesiosaurold from the Niobrara Cretaceous of Kansas, vinder the nan^e of 

 Cimoliasaurus snovii. Through the kindness of Prof. Williston, I have 

 had the opportunity to examine the specimen, and I have been able to 

 make some observations on the structure of the skull, which supplies an 

 important desideratum in our information on the subject. 



In a paper in which I endeavor to trace the homologies of the cranial 

 bars of the Reptilia,* I ascribe f to the Sauropterygia a single postorbital 

 arch, and state that the available evidence is to the effect that this is the 

 zygomatic. I remark, "The supratemporal has no anterior connections 

 according to this author " (Von Meyer on Nothosaurus), "and the supra- 

 mastoid is not described. From all that I can gather from Owen's figures 

 and descriptions of Plesiosaurus, the structure is the same, which is con- 

 firmed by observation on such imperfect specimens as are accessible to me." 



Examination of Williston's specimen shows that there is but one postor- 

 bital bar, and that this is partly the zygomatic, since it extends to the 

 distal extremity of the quadrate, and encloses with it a small Z3'gomatic or 

 quadratojugal bone. But the posterior part of the arch includes also a 

 large supratemporal, as in many Testudinata. Above the supratemporal, 

 aud forming the parietomastoid arch, is the separate element which I have 

 referred to in tlie above quotation as supratemporal, but which it is now 

 clear is the supramastoid. It is then homologous with the element in 

 Ichthyosaurus and in the Cotylosauria, which I have called by that name. 

 This discovery enables me to demonstrate the correctness of my supposi- 

 tion made in the paper already quoted (pp. 19-22), that the postero-lateral 

 process of the parietal bone, so characteristic of Sphenodon and Lacertilia, 

 really includes the supramastoid element. There is no question about 

 the distinctness of this element from the parietal in the Cimoliasaurus, and 

 the suture is shown in the outline figures given by Williston in his descrip- 

 tion referred to. The suture between it and the supratemporal is not so 

 distinct, but is nevertheless visible. The following figure is copied from 

 "Williston, with the sutures inserted as I observed them. 



♦■'On the Homologies of the Posterior Cranial Arches in the Reptilia," Trans. Amer. 

 Philos. Soc, 1X92, p. 11. 

 t L. C, p. 21. 



