APPENDIX. 
Art. XI.—New Characters of Mosasauroid Reptiles; by 
Professor O. C. MarsH. With Plate L 
THE Mosasauroid reptiles are so rare in Europe that the type 
specimen described by Cuvier still remains the most perfect yet 
discovered there, and the only one from which important char- 
acters have been made out. In this country, however, this 
group attained a marvelous development, and was represented 
by several families, and numerous genera and species. The 
abundance of specimens is perhaps best illustrated by the fact 
that the Museum of Yale College contains remains of not less 
than 1,400 distinct individuals. In not a few of these, the 
skeleton is nearly if not quite complete, so that every part of 
its structure can be determined with almost absolute certainty. 
From this store of material, I have already made out various 
characters of these reptiles,* and in the present communica- 
tion several others are recorded, which have escaped the atten- 
tion of previous observers. The subject is by no means 
exhausted. 
THE STERNUM. 
gate in form, and nearly or quite symmetrical, as shown in 
Plate I, figure 1. It is thin, slightly concave above, and con- 
vex below. Its antero-lateral margins are short and rounded, ce 
and have distinct grooves for the coracoids. The costal mar- 
gins are much longer, and converge posteriorly. Each has facets 
for five sternal ribs, and, behind these, false ribs were supported 
by a partially ossified pedicle, which joined the end of the 
Sternum. The ossification of the sternum was by endostosis. 
* This Journal, vol. i, p. 447, 1871, vol. iii, p. 448, 1872. hee © 
t Vertebrata of the Sretaceous, p. 114, 1875, Also, Bulletin of Survey of — 
Territories, p. 309, 1878. me 
