Mekriam.] 



Triassic Ichthyopterygia . 



87 



vertebrae of Baptanodon from the Jurassic, of Western North 

 America, in order to determine whether possibly that genus is 

 descended from Shastasaurus. The vertebra are, however, of 

 the Ichthyosaurus type, and Baptanodon can not be considered as 

 derived from the typical Triassic forms of this region. 



Should the classification of Baur (1887, p. 4) be accepted 

 and the Ichthyopterygia be divided into three families, the 

 Mixosaurida\ Ichthyosauridse, and Baptanodontidae, it will be 

 necessary to add the representatives of the Shastasaurus group 

 as a fourth division, for which the name Shastasauridae is 

 proposed. The distinguishing characters of this family will be 

 founded in the peculiar articulation of the dorsal ribs, the form 

 of the pelvic arch, and the presence of long-spined chevrons. 

 If it is found advisable to bring all the genera of the Ichthy- 

 opterygia together in one family, Shastasaurus and its relatives 

 should be grouped in a distinct sub-family, the Shastasaurinas. 



DISTRIBUTION AND SYNONYMY. 



That of a group of marine reptiles with the characters of 

 Shastasaurus would be confined within very narrow geographic 

 limits is improbable, particularly as the occurrence of its remains 

 points toward a fairly deep and open sea as its habitat. With a 

 view to determining whether any of the Triassic Ichthyosaurian 

 material described from other regions could possibly be consid- 

 ered as Shastasaurian, the writer has gone over such literature 

 as is accessible to him, and the following list of species referred 

 to the Triassic, outside of California and Nevada, has been 

 compiled. 



Mixosaurus atavus Quenstedt. 



Mixosaurus cornalianus Bassani. 



Mixosaurus riprdenskjb'ldi Hulke. 



Ichthyosaurus (?) polaris Hulke. 



Ichthyosaurus (?) rhceticus Sauvage. 



Ichthyosaurus (?) carinatus Sauvage. 



Ichthyosaurus (?) hectori Lydekker. 



Practically all of these species have been founded on very 

 fragmentary material, in which a genus with characters like those 

 of Shastasaurus might escape detection unless nearly perfect 



