220 University of California Publications. [Geology 



cases the suggestion of foramina on the expanded distal end may 

 indicate that these particular specimens are humeri. 



In the same deposits with the larger limb elements are a num- 

 ber of smaller and more slender bones with less expanded ends. 

 Though it is not possible to distinguish these certainly from those 

 determined as propodials, it is probable that some of them rep- 

 resent epipodials or podials (pi. 17, figs. 4 and 5). 



Vertebrae and Ribs. 



Numerous isolated vertebrae were found in the lower portion 

 of the upper, massive division of the Hosselkus Limestone on 

 Brock mountain, and in the limestones along the North Fork of 

 Squaw Creek. The vertebrae are always scattered, and as yet no 

 connected series representing these forms is known. The upper 

 arches are closely connected with the centra in nearly all cases. 

 Only in a few instances can the line of division between them be 

 distinctly seen, and in most instances the connection is so intimate 

 that even the suture is almost obliterated. 



The centra are all biconcave, but the terminal faces are in 

 general not deeply cupped. In a single instance a somewhat 

 broken centrum (No. 10806) was found which is gently concave 

 toward the periphery of the faces, but is much more sharply 

 excavated near the middle. The centrum is also relatively short 

 anteroposteriorly, so that the anterior and posterior concave faces 

 almost meet in the middle. This specimen possibly represents a 

 middle or a distal caudal centrum of Nectosaurus, or may repre- 

 sent an ichthyosaurian genus. 



The centra are about as long as high in most cases. There is 

 evidently some variation in different regions of the column, the 

 length being in some instances slightly greater and in others 

 somewhat less than the height, as is indicated by the measure- 

 ments below. 





Length of 



Height of 



Height of Number of lateral 





centrum 



centrum 



Neural arch 



apophyses 



No. 10774 (dorsal?) 



6 m.m. 



5.3 



11.5 



2 



No. 10627 (dorsal?) 



6 



6.5 





1, large 



No. 10787 (dorsal?) 



7.7 



8.4 



a 16.5 



2 f 



No. 10779 (caudal) 



5.2 



5.2 



13 slender 



none 



No. 10806 



o 4.5 



a 7 







a, approximate. 











No. 10806, possibly ichthyosaurian. 



