0. 0. Marsh—Structure of Mosasauroid Reptiles. 4651 
longest digits had six phalanges and the shortest but four. 
Moreover, that the paddle was expanded as in some of the 
aceans, and not contracted as in Ichthyosaurus, Plesiosaurus, 
and other Enaliosaurs. Another os of interest jis, that, in 
evelopment. The humerus was even shorter and stouter, an 
the whole paddle apparently broader in proportion. In Rhino- 
Saurus, the anterior limbs were proportionally much smaller, 
and more slender. 
8. Posterior Limbs. The absence of these extremities in the 
oe limbs in nearly all the other genera was soon after ob- 
—. while investigating the subject, and at the present time 
ere can be no reasonable doubt that they are common to the 
— arch, however, presents some peculiar features, and its 
ements, which are here figured for the first time, deserve @ 
me 
The acetabulum was formed by the coadapted ends of the 
* This Journal, vol. i, p. 447, June, 1871. 
