1911] 



Merriam: Saurian Fauna of Spitzbergen. 



325 



genus Phalarodon, 10 but in this and in other somewhat similar 

 primitive ichthyosaurs the teeth are in a single row, and the low- 

 crowned posterior teeth rapidly change to a sharply conical form 

 in the middle and anterior region of the jaw. In all of the char- 

 acters mentioned, excepting in the folded roots, the peculiar 

 teeth on most of the specimens figured by AViman resemble the 

 dentition of the genus Omphal&saurus from the Middle Triassic 

 of Nevada. 11 



Omplialosaurus was described from a single specimen repre- 

 senting a skull with a portion of the dentition. A few vertebrae 

 were connected with the skull, and several limb bones were doubt- 

 fully associated with it. The structure of the skull was not 

 clearly understood, but it did not seem to correspond to that of 

 any known reptilian family. The inferior dentition consisted of 

 several rows of hemispherical, to low-conical teeth on each 

 dentary. The inferior dentition collectively formed a strongly 

 convex crashing surface, which presumably indicated that the 

 facial region was short. Other specimens which have been 

 obtained at the same horizon as the original one show the denti- 

 tion better than in the type. In each case the tooth-crowns 

 preserve a nearly unvarying form, and t^Pe surface of the tooth- 

 pavement is convex. 



Other skeletal remains which have been thought by Wiman 

 to represent the same genus as the jaws bearing hemispherical 

 teeth comprise a number of vertebrae and many elements rep- 

 resenting the limbs and arches. The vertebrae are not distinctly 

 different from those of certain Triassic ichthyosaurs. So far 

 as can be determined this may also be true of the vertebrae as- 

 sociated with the type specimen of Omplialosaurus. The limb 

 bones referred to Pessopteryx are all such as might belong to an 

 ichthyosaur of the type of Shastasaurus. Short limb elements 

 of a similar nature were associated with the type specimen of 

 Omplialosaurus, but were not described, as there seemed a possi- 

 bility that the association was purely accidental. While one 



10 Merriam, J. C, Univ. Calif. Publ. Bull. Dept. Geol. vol. 5, p. 383. 

 1910. 



11 Merriam, J. C, Univ. Calif. Publ. Bull. Dept. Geol. vol. 5, p. 76. 1906. 



