[ 155 ] 
ON SOME NEW AND LITTLE KNOWN CREODONTS. 
By W. B. Scott. 
Genus MESONYX. 
I. Mesonyx obtusidens. 
The Princeton Scientific Expedition of 1886 had the good fortune to obtain at 
Twin Buttes, Wyoming, an unusually perfect skeleton of Mesonyx obtusidens, from 
which all the important characters of the genus may be made out. This will enable 
us to clear up some of the confusion which still prevails as to the early eocene flesh- 
eaters of North America. The few deficiencies in the chief specimen are nearly all 
supplied by other individuals from the same region. The only bones not represented 
in the collection are : (1) two sacral and (2) several caudal vertebra}, (3) the distal end 
of the femur, (4) the central, (5) the rudimentary 1st metacarpal, (6) the entocun- 
eiform. A restoration may thus be made which offers very little opportunity for 
error (PI. V). 
The Skull. — This is the most remarkable part of this very pecidiar animal; the 
exceedingly small brain capacity, (less even than in Thylacymis), the immense sagit- 
tal cre.st, the very long and wide zygomatic arches, the narrow and lofty occiput, and 
the great length of the muzzle, strike one at the first glance (PL ^ I.) 
The hasi-occipital is broad and flat, the exoccipitals very narroAv, the condyles small 
and directed strongly outwards; the paroccipital processes are short and stout and 
arise very close to the condyles. The supra-occipital is very high, narrow and re- 
curved, so that when the skull is in a horizontal position the summit of the occiput pro- 
jects considerably beyond the condyles. The supra-occipital is shaped like a narrow 
lanceolate Gothic arch, and as a whole the occiput is in strong contrast to that of 
the Carnivora. 
The base of the cranium is somewhat injured, so that it is difficult to make out 
the relationships of the tympanic and periotic. A very small and apparently undivided 
bulla is present. 
The hasi-sphenoid is likewise broad and flat ; the aU-splienoids small and appar- 
ently pierced by an ali-sphenoid canal. The parietals are very large, but comparatively 
little of them is applied to the wall of the brain cavity, the greater part going to the 
formation of the very high and thin sagittal crest, which gives much of its most curious 
physiognomy to the head. The appearance of this part of the skull is very similar 
22 JOUR. A. X. S. PHILA., VOL. IX. 
