jtrassic yi:i;tep>i;ate fossils. 



491 



form it arc nearly equal in size and general proportions. They are firmly 

 coossified, and their transverse processes arc ankylosed to the centra. 

 Those "iL each side arc united distally into a solid mass, which rests on the 

 short ilium. The articular tares of the sacral vertebrae arc nearly plane. 

 That of the anterior centrum is a transverse oval in outline, and the 

 posterior face i> more nearly round. The centra ami their processes are 

 somewhat lightened l>v cavities, as in the sacrum of Atlantosaurus. 



Flo. 38.— Pelvis of Ipatosaurus ajaa ; seen from the left. 0ne-9ix1eenth natural i 

 acetabulum I foramen in pubis ; il ilium; iii, "ischium ; p, pubis. 



The type species of the present genus is Apatosaurus njii.i Marsh, and 

 the known remains indicate a reptile at least 50 feet in length. A much 

 larger species is indicated by various remains from the same locality in 

 Colorado, among which is the huge cervical vertebra represented in fig. 36. 



