157 



McanKrcments. 



u. 



Length of tlio (■fiitnim <if (lie antfiior viMtcbni 0. Ofi-l 



Diameter of tlie ball, vertical 0. 0:!0 



Diameter of the linll, transverse 0.039 



Length of t lie posterior 0. 0(j-1 



Diameter of the ball, vertical 0. 0:!0 



Diameter of the ball, horizontal 0. Oi:i 



Expanse of the anterior zyfjapojihyses 0. 05r> 



The first vertel)ra was louud by (he wriler at tlic loot ol' a bliill' on tlio 

 lower part of Butte Creek; the second was procnicd bv Prot". B. F. Mndire, 

 from a poinl one mile sonihi'ast of Slicridan, iicai" the North Fork of 1hi- 

 Smoky Kivcr. 



It is this species that T compared with the Mosasaurus deprcssiis, Cope, 

 in a report on (Jie collection made by Profpssf)r Miidge (Proceedings of (he 

 American Philosophictd Society, 1871. p. 1G8). The size is similar, but tin; 

 form of the articular surfaces of the vertebrae is very diflferent. 



Platecarpus mudgei, Cope. 



The characters dislinguishiug this saurian are the following: Vertebrae 

 without rudiinenlal zygospheii; ([uadrate bones with plane surfaces from the 

 proximal articular surface and the external obtuse-angled ridge to the meatal 

 pit; tiie latter, therefore, not sunk in a depression as in the other species. 



'Vhe determination of I his species rests on a series of specimens from the 

 yellow chalk at a point six miles south of Sheridan. Kaiis. They consist 

 of three vertebrie and traguieuts of atlas, with numerous por(i(jns of cranium 

 and proximal extremity of scapula. 



The iiarts of cra/^wm preserved are the frontal bone without the anterior 

 extremity, and with the adjacent parietal almost complete; j)arts of the basi- 

 sphenoid ; the suspensorium ; the ossa tpiadrata; and the greater part of tlie 

 surangular. The frontal is flat, witii thin edge, longitudinally hollowed on eatdi 

 side of the median line, wiiicli is marked by a low but acute keel. There is 

 an abundance of foramina and delicate grooves on the surface, and. posteriorly 

 elevated striae, which converge to the median keel. Thi; median square ex- 

 tension of the i)order of the parietal :s in tidvance of the lateral portion ol'tiie 

 same, and not behind it as in Clidastes i»opython. The t()ntunclle is large. 

 A marked feature is that the parietal crests unite into a low median ridge a 

 short distance behind tlu^ f()iitan(^lle, and are not. as in ('. jiropi/thon, separated 

 by a horizontal plane. The sntnn^s of the l)ones fonninir the side oi" the brain- 



