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University of California Publications. [Geology 



would not be justified in holding that all of the limb elements 

 referred by "Wiman to Pessopteryx actually represent the same 

 genus as the jaws with button-like teeth, there seems a reasonable 

 possibility that some of them belong to that group. 



It seems to the writer probable that some, if not all, of the 

 Spitsbergen forms with button-like teeth arranged in several 

 rows are referable to a genus closely allied to Omphalosaurus. 

 It would not be surprising if there were associated with these a 

 number of specimens of ichthyosaurs of the Phalarodon type. 

 This is at any rate precisely the association found in the Middle 

 Triassic of Nevada. 



FAUNAL BELATIONSHIPS 



The saurian forms represented in the Triassic of Spitz- 

 bergen show a noticeable similarity to those of the Triassic of 

 western North America and of central and southern Europe. 

 Mixosaurus ( ?) nordenskioldii of Spitzbergen is apparently close 

 to Mixosaurus cornalianus of Italy, and seems also nearly identi- 

 cal, so far as known, with M. (?) natans of the Middle Triassic 

 of Nevada. Some of the Spitzbergen forms referred by Wiman 

 to Mixosaurus show a general similarity of the dentition to that 

 of M.( °!)atavus of central Europe, as also to that of Phalarodon 

 of the Middle Triassic of Nevada. The resemblance of some of 

 the Spitzbergen specimens included in Pessopteryx to Omphalo- 

 saurus of the Nevada Middle Triassic is such as to suggest close 

 relationship, if not generic identity of the two forms. 



The stage of evolution of the Spitzbergen fauna is not easily 

 estimated with the material available. As nearly as can be deter- 

 mined M. ( ?) nordenskioldii is near the stage of evolution of M. 

 cornalianus and M. (?) natans. It may be slightly less advanced 

 than Cynibospondylus, but difference in size of the individuals 

 compared may prevent a satisfactory determination of the rela- 

 tive stages of advance. 



The forms of the Pessosaurus polaris type in the Spitzbergen 

 fauna suggest the stage of evolution seen in Shastasaurus of the 

 Californian Upper Triassic. It should, however, be stated that 

 fragmentary specimens of a somewhat similar nature have been 



