O. C. Marsh—Limbs of Sauranodon. 171 
In Ichthyosaurus, the intermedium is not entirely excluded 
from the epipodial row; in Plesiosaurus and all other reptiles 
the process is essentially completed. In some Amphibians, 
this bone still separates the lower ends of the two specialized 
bones above it. Sawranodon marks an earlier and most inter- 
esting stage in the differentiation, and, taken in connection 
with the examples here cited, indicates clearly how the trans- 
ition was accomplished. 
he six complete digits in the limbs of Sawranodon is a 
character not before observed in any air-breathing vertebrate. 
Some of the Amphibians retain remnants of a sixth digit, an 
Ichthyosaurus often has, outside of the phalanges, one or more 
rows of marginal ossicles that probably represent lost digits. 
With these exceptions, the normal number of five digits is not 
exceeded. 
Sauranodon discus, sp. nov. 
te of the skull much elongated, and the snout slender. 
emargination. 
the species here described, which is based upon the 
greater portion of a skeleton, the coracoid is more deeply 
emarginate, and the head of the humerus rounded, nearly as 
much as that of the femur. The paddles, also, are broader 
Mm proportion to their size, than in the type species, and other 
Yale College, New Haven, Jan. 24th, 1880. 
