Merriam.] 



Triassic Ichthyopterygia. 



99 



or anterior dorsal region. The height of the rib-head shows that 

 the diapophysis is not abnormally shortened owing' to extensive 

 articulation of the tuberculum against the upper arch. The 

 very rudimentary parapophyses would, taken by themselves, 

 point to a more posterior position in the column than is suggested 

 by the other characters. The form of the cross-section and 

 length of the diapophysis are, however, more nearly constant 

 characters than the relative size of the disappearing parapophysis, 

 and it seems to the writer that in this form the reduction of the 

 parapophyses has possibly gone farther in the cervical region than 

 in the other known species. 



The dimensions of these vertebrae and ribs show that the 

 individuals to which they belonged ranked among the largest 

 known Ichthyopterygia. If the centrum just described be supposed 

 to belong as far back in the column as the tenth in osmonti, and 

 if the ratio of its size to that of the thirty-fifth were the same as 

 in that species, the thirty-fifth would have a diameter of 245 mm. 



Although the quantity of material at hand is insufficient for 

 satisfactory diagnosis of this form, it would seem that the 

 shortness of the centra, the possible unusual redaction of the 

 parapophyses, and the large size, indicate a distinct species. It 

 is, of course, possible that all of these characters could belong 

 to old individuals of some of the other forms described. It 

 appears very doubtful to the writer, however, whether the 

 centra would become relatively shorter with age; while greater 

 reduction of the parapophyses would almost be expected in one 

 of the larger species of the genus. 



The following are the measurements of the type specimens of 

 careyi: 



Width of rib-head 55 mm. from proximal end 55 mm. 



Estimated width of rib-head at proximal end 75 



Width of second centrum.. 180 



Height estimated certainly within 5 mm. of actual size.. 160 

 Length of centrum 60 



Shastasaurus altispinus n. sp. 



Pl. 14 , FIG. 5, AND Pl. 15. 



The specimens representing this species were found embedded 

 in two loose slabs lying close together at the foot of a steep 



