Merhiam.] 



Triassic Ichthyopterygia . 



69 



Practically the whole work of preparation was done by Mr. 

 Eustace Furlong, to whom the writer is greatly indebted for his 

 patient and skillful handling of this most refractory material. 



CHARACTERISTICS OP SHAST ASAURUS . 



The material serving as the foundation for this discussion 

 includes considerable parts of seven individuals, together with 

 many isolated bones and teeth. They represent nearly the whole 

 of the skeleton, excepting the anterior part of the skull and the 

 distal portions of the paddles. 



All of the specimens seem to belong to one group, which is 

 recognized as the genus Shastasaurus . Considerable differences 

 among them are held to be of less than generic value. In addi- 

 tion to the type species, 8. pacificus, five new forms perrini, 

 osmonti, alexandrce, careyi, and altispinus have been recognized. 



Vertebrae and Ribs. — Good material for the study of the 

 vertebral column is furnished by a specimen of osmonti (Pis. 8 

 and 9) with which there is a good series of thirty-five vertebras 

 extending back from a point close to the head, with few if any 

 interruptions. A specimen of perrini (Pis. "> and 7) has an 

 unbroken series of eighty vertebra? running from the anterior 

 dorsal region to the posterior portion of the tail. In a specimen 

 of alexandrce (PI. 12) fourteen or fifteen vertebrae lie immediately 

 behind the skull. 



The centra are deeply biconcave in all regions of the column. 

 The concave surface begins close to the periphery and slopes 

 sharply but evenly to the the middle. No case of normal perfora- 

 tion of the centrum has been discovered, though the partition 

 between the concave surfaces is frequently very thin. In a single 

 specimen it was possibly cut through by a minute canal. The 

 upper arches are always free from the centra, and seem to have 

 been separated from them by thick pads of cartilage. Excepting 

 in the dorsals and anterior caudals of perrini, the longitudinal 

 diameter of the centra is very much shorter than either the ver- 

 tical or the transverse. In the vertebrae of perrini just mentioned 

 the length may be two-thirds to three-fourths of the height. 



In the cervical region the centra are somewhat broader than 

 high. Through the greater part of the dorsal region these two 



