AMERICAN JURASSIC PLESIOSAURS 349 
It is improbable that the Jurassic plesiosaur Plesiosaurus shirley- 
ensis Knight" belongs to the genus Plesiosaurus.2. The vertebrae, 
2a. 
Fic. 2.—Tricleidus Andrews. 2a, left paddle of T. laramiensis Knight, x4. 
2b, pectoral paddle of T. seeleyz Andrews, X}. 
however, seem to separate M. reedii from this form. Quoting 
from Professor Knight’s description of P. shirleyensis: 
The vertebrae are slightly biconcave, and all wider than long; but in the 
dorsals and posterior cervicals the length and breadth are nearly equal... . . 
On the anterior caudals the neural spines are of considerable height. Nothing 
t Knight, Am. Jour. Sct., IV, 115. 
2S. W. Williston, North American Plesiosaurs, Pub. Field Columbian Mus., 
Geol. Series, II, No. 1, p. 7. 
