350 MAURICE G. MEHL 
of importance is known of the dorsal vertebrae, excepting that they are slightly 
biconcave and circular in transverse sections.’ Anterior caudals are flattened 
beneath and have two large circular facets for the articulation of the chevrons; 
neural arches firmly attached to centra. 
The type material of P. shirleyensis is so fragmental that one 
cannot be certain of the distinguishing features. 
Tricleidus? laramiensis Knight 
The following description is based on a part of the original 
specimen described by Knight as Cimoliosaurus laramiensis.t 
In the past Cimoliosaurus Leidy has been made a sort of catch-all 
for the remains of imperfectly known plesiosaurs. The genus, 
however, was described from vertebrae alone? and, therefore, till 
it is better known, a species can be referred to it with certainty 
only on evidences furnished by the vertebrae. In Leidy’s descrip- 
tion of the type, C. magnus,3 he figured what he took to be two 
dorsal and eleven lumbar vertebrae. I believe that Dr. Williston 
was right, however, when he referred Figs. 13-109, Pl. 5, in Leidy’s 
description, to the cervical region, Figs. 1-5, Pl. 6, to the dorsal, 
and Figs. 6-19, Pl. 6, to the cervical region.4 The caudals of 
Discosaurus Leidy, described in the same work, along with Cimolio- 
saurus and later shown by Cope to be identical with that genus, 
have a pair of ridges extending antero-posteriorly along the ventral 
surface. The vertebrae of Cimoliosaurus, then, have certain generic 
characteristics, but none of these is mentioned by Professor Knight 
in his description of C. laramiensis. In fact, the only character- 
istics mentioned are ‘‘the forward overhanging” of the dorsal 
centra and the large angular chevron facets of the caudal vertebrae 
and neither of these is noted in the type specimen. Furthermore, 
Cimoliosaurus is typically an Upper Cretaceous form. The species 
here described is, therefore, provisionally placed with the English 
genus Tricleidus Andrews,> the pectoral paddle of which is very 
t Am. Jour. Sct., 1V, X, 117. 
2" Prog. Nats Acad’ Sct: Phila. Ta5l, 325508545 725 pla 2sM1eSs Aenc, 0. 
3 Smithsonian Contributions to Knowledge, XIV, 25-20; pl. 5; figs. 13-19, and pl. 
6; figs. 1-10. 
4 Am. Jour. Sci., XXI, 222. 
5 Andrews, Marine Reptiles of the Oxford Clay, Part 1, p. 149. 
