1915.] Matthew and Granger, Lower Eocene Wasatch and Wind River Faunas. 8o 
cated by the adaptive features of the teeth. The cusps are blunt-pointed 
and were subjected to an extreme degree of wear by the nature of the food; 
but the long slender and rather weak jaw is quite unsuited to crushing bones, 
and the entire lack of shearing teeth is equally unsuited to cutting flesh or 
tendons. The hyzena, usually regarded as a typical carrion-eater, has 
teeth of wholly different character, paralleled by Patriofelis among the 
Creodonts. The Mesonychid teeth may perhaps have been adapted to 
crushing fresh-water molluscs or some similar food that would involve a 
great deal of wear of the cusps without entailing any great strength of Jaw. 
They certainly are not suited either for bone-crushing or flesh-cutting, nor do 
they appear suitable for omnivorous or frugivorous habits; they are neither 
pig-like nor bear-like, and the hoof-like claws are not consonant with 
digging nor the snout with rooting habits. | 
I do not know of any parallel adaptation among modern mammals, but 
the Fayum Apterodon shows a notable approach to the Mesonychid style of 
teeth. In this genus, however, if Andrews’s association of the skeletal parts 
be correct, the limbs indicate some degree of natatorial adaptation, while in. 
the Mesonychide the adaptation appears to be progressively cursorial. 
This is not inconsistent with the suggestion of feeding on fresh water mol- 
luses; the Mesonychide show the cursorial adaptation only in the smaller 
phyla, which would presumably be inoffensive animals requiring means of 
escape from carnivorous enemies, while A pterodon if of similar food adapta- 
tion might readily become aquatic. | 
Key to Genera of M esonychide. 
A. Molars 3; metaconids well developed, paraconids smaller, especially on psa and 
m3; pollex complete in D. saurognathus..............-. +00 555. Dissacus. 
B. Molars 3; metaconids vestigial; paraconids large on ps—ms; pollex vestigial. 
Pachyena. 
C. Metaconids absent, paraconids large on p4—Ms. 
1. Molars 3; limbs and feet slender, pollex vestigial.......... Synoplotherium. 
2. Molars%; limbs and feet very slender, pollex vestigial or absent. . . . Mesonyz. 
3. Molars %; limbs and feet short robust, pollex unknown....... Harpagolestes. 
D. Molars 3; metaconids small, paraconids large on m3 teeth highly compressed ; 
sleull’ and. ice Slew an te eee ein coy teen spews Hapalodectes. 
Dissacus Cope 1881.' 
Type, D. navajovius from the Torrejon of New Mexico. 
Generic distinctions: Metaconids distinct on mis; paraconids weaker especially 
on m3; pollex (?) complete; humerus with entepicondylar foramen. 
1 Amer. Nat., Vol. XV, p. 1018. 
