.MKRKIA.M: TR1ASSIC ICHTIIVOSAURIA. 



11.-) 



this portion of the column the bicon- 

 cavity of the contra is reduced to a vein- 

 small area in the middle of each artic- 

 ular face, outside of which the surface is 

 nearly plane. 



In the middle caudal region the dia- 

 pophyses air short and round, and have 

 risen almost to the middle of the sides 

 of the centra. The vertical transverse 

 cross-section of the centra has also 

 changed to a narrow hexagonal form. 



The upper arches of the cervicals 

 possess strong zygapophyses (pi. 8), on 

 which the lateral faces are well sepa- 

 rated and do not fall into the same plane, 

 as occurs in IchtJtt/owiurus. In the 

 dorsal region the zygapophyses are still 

 well developed and the facets separate. 

 In the caudal region the zygapophysial 

 facets are much reduced, although the 

 anterior and posterior projections of 

 the upper arches are retained on most 

 of the vertebrae. 



The neural spines of the cervicals 

 are somewhat compressed laterally, but 

 are generally thicker than in Ichthyo- 

 Miiirnf!. In the dorsal region the spines 

 are still considerably thickened. In no 

 case, however, does the thickening of the 

 spines approach that of Shastasaurus 

 (ilti^j)iinis. In the caudal region of 

 specimen 9950 the neural arches are con- 

 siderably lower and thinner than in the 

 dorsal region. 



The form, and most of the import- 

 ant characters, of the caudal region are 

 well shown in a large specimen of C. 

 ixii-huift (no. 9947), in which there is 

 present an excellent series of 59 verte- 

 brae, aggregating twelve and one-half 

 feet in length (fig. 132). The series be- 

 gins near the pelvic region and extends 



