NORTH AMERICAN PLESIOSAURS 735 



Family Polycotylidae Cope 

 Skull with long facial rostrum and thin, high parietal crest. Supraoccipital 

 bones separated. Palate with large interpterygoidal vacuity, the pterygoids 

 articulating with vomers, and meeting in the middle line posteriorly; no palatine 

 foramina. Neck but little longer than head, the vertebrae all short; ribs single 

 headed. Coracoids meeting throughout in symphysis, with long clavicular 

 processes articulating with clavicles and scapulae, the interclavicle present; a 

 large interclavicular foramen; ischia elongate. Three or four epipodial bones, 

 all broader than long. Colorado Cretaceous, North America. 



Polycotylus 



Cope, Proc. Amer. Phil. Soc, XI, 117, 1869; Williston, Amer. Journ. Sci., 

 XXI, 233, March, 1906. 



P.) latipinnis Cope, loc. cit.; Ext. Batrachia, etc., 36, pi. i, ff. 1-12; An. Rep., 

 U. S. Geol. Surv., 1871, 388; ibid., 1872, 320, 335; Bull., U. S. Geol. Surv. 

 Terr., 27, 1874; Cretac. Vert., 45, 72, 255, pis. I, VII, ff. 7, 7a; Leidy, Ext. Vert. 

 Fauna, 279; Williston, Field Mus. Publ., No. 73, p. 67, pi. XXI; Amer. Journ. 

 Sci., 2, 234, pi. Ill, Niobrara Cretaceous, Kansas. 



P.) dolichopus Williston, Amer. Journ. Sci., XXI, 235, pi. Ill, f. 2; Niobrara 

 Cretaceous, Kansas and Wyoming. 



Trinacromerum 



Cragin, Amer. Geologist, December, 1888, p. 404; September, 1891, p. 171; 

 Williston, Amer. Journ. Sci., XXI, 236; Dolichorhynchops Williston, Kans. 

 Univ. Sci. Bull., No. 9, p. 141, September, 1902; Field Mus. Publ., etc. 



T.) bentonianum Cragin, loc. cit. Fencepost horizon of Benton Cretaceous 

 Downs, Kansas. 



T.) osborni Williston, loc. cit.; Amer. Journ. Sci., XXI, 234; Field Mus. Publ., 

 No. 73, pp. 1-5 1, pis. I-XVII {Dolichorhynchops). Niobrara Cretaceous, Kansas. 



T.) anonymum Williston, loc. cit., p. 45, pi. XVIII. Upper Benton 

 Cretaceous, Kansas. 



T.) latimanus Williston, antea. — Hailey Shales, Upper Benton, Wyoming. 



Piratosaurus 



Leidy, Cretac. Rept. N. Amer., p. 29, 1865. 



P.) plicatus Leidy, loc. cit., pi. XIX, f. 8. Cretaceous, Manitoba. 



As has been suggested, this genus is perhaps identical with Polycotylus or 

 Trinacromerum, in which case the name must take priority. If so, the determina- 

 tion cannot be made with certainty until such time as more complete specimens 

 from the type, locality, and horizon have been studied. 



The above species are all that are known belonging to the group. It is 

 possible that other forms from the Fort Pierre may eventually be found, per- 

 haps some have been described under other names. I may add here that the 

 type of Nothosaurops occiduus Leidy is unquestionably a Champsosaurus Cope, 

 as was suggested by Zittel, and that name should take precedence. 



