34 



.MEMOIRS OP THE UNIVERSITY OF CALIFORNIA. 



The neural spines of the vertebrae of Miro<tnn{x (tig. 123) as figured by Repos- 

 si, appear to be thin and flattened distally, but a prominent rib is present along 

 the lateral face of the arch, and extends for a considerable distance up on the 

 side of the spine. In the cervical region of all the American Triassic forms 



3 la 



31c 



32a 



32c 



33b 



33a 



33c 



Figs. 31o-31c. Shastascmrus osmoiiti Merriam. Neural arch of a dorsal vertebra, X V->. Fig. 31a, 

 lateral view; 316, cross-section of summit of neural spine; Sic, anterior view. 



Figs. 32a-32c. Delphinosaurus perrini Merriam. Neural arch of a dorsal vertebra, X %. Fig. 32a, 

 lateral view; 326, cross-section of summit of neural spine; fig. 32c, anterior view. 



Figs. 33a-33e. Shastasaurus atispinus Merriam. Neural arch of a dorsal vertebra, X l /->. Fig. 33a, 

 lateral view; 336, cross-section of summit of neural spine; 33c, anterior view. 



the neural spines are so thick as to be nearly round in cross-section. In the 

 dorsal region the spines may be greatly broadened anteroposteriorly and be- 

 come quite thin distally (fig. 32&). This change from thick spines on the cer- 

 vicals to broad, thin ones on the dorsals is well shown in Delphinosaurus perrini 

 (pi. 7, fig. 2), but even in this form the lateral faces of the spines on the 



