Apr. 1903. NorrH AMERICAN PLESIOSAURS— WILLISTON. ng 
was briefly described by me several years ago under the name of 
Plesiosaurus gouldit. The species is referred to Plestosaurus because 
no better place is known for it; in all probability it really belongs to 
some other genus. The species was based upon several dorsal ver- 
tebre in fairly good preservation, one of which, the best, is herewith 
figured. (Pl. XXVII.) 
The specimen shows little compression, and its form is doubt- 
less normal. The anterior face is rather deeply concave, cordate in 
outline, with a small neural depression above. The anterior zyga- 
pophyses are spout-like, the notch between them not extending 
further than the middle of the articular surfaces. The spine is 
rather’short and small. The transverse processes are compressed, 
springing in part below the neural canal from the base of the arch. 
The body is compressed in the middle, forming an obtusely rounded 
surface below.. “About midway on the sides, below the lower root of 
the transverse processes, the side is pinched in, with a small vascular 
foramen at the bottom of the depression. 
The vertebra described probably belongs near the sacrum. Its 
measurements are as follows: 
Width of anterior end of centrum ; ; see Ab LORIN; 
Vertical diameter, same end : ' aes 
Length of centrum : ; (oY SP He 72) 
Height of vertebra : : , : Lhe gs 
Expanse of transverse processes PG eas 
Width of neural canal : Pagan 
Expanse of anterior zygapophyses ; : wis) 

PROPODIAL BONES OF YOUNG PLESIOSAURS. 
It is an interesting fact that isolated propodial bones of young 
plesiosaurs are not at all rare in the Kansas chalk; no more so indeed 
than are bones of the adult animals. I have seen more than a score 
of such, and four or five are now preserved in the museum of the 
University of Kansas; there are many others in the Yale museum. 
Four of these bones are shown in Pl. XXIII; a fifth one, more immature 
than any of those, is figured in Pl. XXII, Figs. 1-4. All such 
bones are composed of more dense tissue than is observed in adult 
bones. Especially is the structure dense in the youngest specimen 
‘here figured. In this specimen the head of the bone is not at all dif- 
