F. B. Loomis — New Mosasaur from the Ft. Pierre. 561 



articulare, while the coronoid is only a small bone making a 

 low process. In all these features the mandible resembles that 

 of Platecarpus. 



Length of the mandible over all 603 



Greatest depth from coronoid to splenial 136 



Depth under the last tooth 66 mm 



For determining the vertebrae specimen No. 388 aids greatly 

 with its 23 vetebrse in place. On this specimen the first long 



Fig. 3. 



mm 



Fig. 3. The mandible from, the outer side. 1/6 nat. size, a, articulare ; 

 c, coronoid ; d, dentale ; sa, supra angulare ; sp, splenial. 



rib (i. e. probably reaching to the sternum) is on the eighth 

 vertebra. Then follow 10 long ribs, after which the ribs are 

 much shorter. The specimen with 56 vertebrae begins in the 

 middle of the long ribs. There are twelve with short ribs and 

 clearly live which are noncostiferous (at this point the series is 

 disarranged). Following this are 24 anterior caudals with chev- 

 rons, then a break of several vertebrae, followed by 14 caudals 

 from well down in the tail. Williston gives the vertebral 

 formula for Platecarpus as 7 cervicals, 22 dorsals, 5 pygals and 

 80? caudals = 115? for the full series. "With the above, the 

 Amherst specimens agree ; so that if restored the form, Plate- 

 carpus brachycephalus would appear just about as does P. cory- 

 phosus* and would be about 1 5 feet long. 



In the cervical series, the atlas consists of three small nodu- 

 lar pieces, of which two are preserved. The intercentrum is a 

 tiny bone with three principal faces, of which the two upper 

 articular ones are slightly concave, while the ventral one is 

 convex with a slight median prominence for muscular attach- 

 ment. Only one lateral piece is present which is distorted by 

 the infiltered gypsum, but seems to be normal to the genus. 

 The rest of the cervicals have suffered in preservation so that 

 the ends of the spines and processes are crumbled and partly 

 gone. On the axis the odontoid is a separate element, and is a 

 three-sided nodule with a rounded convex anterior surface and 



* Williston, Univ. Geol. Survey of Kansas, vol. iv, plate LXXII. 



