228 S. TU. Williston — Worth American Plesiosaurs. 



tified some of the vertebrae wrongly. The first dorsal verte- 

 bra, as he describes it, is in reality a posterior cervical, while 

 his seventh is either the last pectoral or the first true dorsal. 

 From his description, I make out sixty-two as the number of 

 cervical vertebrae preserved, and eighteen dorsals. As this 

 number of dorsals is smaller than is known in any other 

 species of plesiosaurs, I am confident that the series was not 

 complete. If Cope was correct in the serial relations of the 

 cervical vertebrae described, the species is quite distinct from 

 anything otherwise described. His descriptions of the pec- 



Figtjre 2. — Scapulae and coracoids of Elasmosaurus snowii Williston. 

 Specimen No. 636, Yale Museum. 



toral and pelvic girdles and of the limbs indicate an excellent 

 specimen now in the Field Museum, which will be shortly 

 described by Mr. E. S. Riggs, and a perfect humerus from 

 the Hailey shales in the collection of the University of 

 Chicago. 



Elasmosaurus snowii Williston. Niobrara Cretaceous of Kansas. 



This species, based upon an excellent skull and a connected 



series of eighteen cervical vertebrae in the museum of the 



University of Kansas, I identify with much certainty in an 



