Brachysaurus, a New Genus of Mosasaurs. 
BY S. W. WILLISTON. 
With Plate VIII. 
The University Geological Expedition of 1894 was fortunate in 
discovering in the Ft. Pierre deposits, of South Dakota, two re- 
markable specimens of Mosasaurs, one of them representing a new 
species of Mosasaurus in remarkably perfect preservation, the other 
a:new genus: A brief reference to the most peculiar characters 
presented by the species representing this genus was given by 
me in this journal, Vol. III, p. 169, under the specific name 
Overtoni, from its discoverer, my assistant. I did not feel sure of 
its distinction from some of the forms previously described, and 
refrained from giving the genus a name. Its characters are, how- 
ever, peculiar in so many respects that I venture to more fully 
describe it in the present communication under the name Brachy- 
saurus. 
The horizon whence the specimen was obtained is near the top 
of the Pierre deposits of the Cheyenne river of South Dakota, and 
probably a hundred or more feet above that of Mosasaurus horridus 
described by me. It thus, it is seen, represents one of the latest 
forms hitherto made known from North America. That it may be 
found identical with some of the forms hitherto described from 
fragmentary material from New Jersey under names that have been 
supposed to be synonymous with better known genera, 1s not im- 
possible. The generic name here proposed is, therefore, in a 
measure provisional. 
The material upon which the genus and species are based is as 
follows: One mandible neatly complete, both maxilla, the most of 
the frontal bone, one quadrate, portions of the very massive ptery- 
goid, and other fragments of the skull; some twenty or more ver- 
tebrae in more or less imperfect preservation; both humeri; and 
two smaller paddle bones. The generic characters, derived from 
these parts of the skeleton, are as follows: 
(95) KAN, UNIV. QUAR, VOL, VI, NO. 2, APRIL, 1897, SERIES A. 
