1892.] NATURAL SCIENCES OF PHILADELPHIA. 305 



P2 which is somewhat larger and has a tritocoiie; Pa is similar but 

 larger and P4 is completely molariform, but the triiocone is smaller 

 than the protocone. The molars have very massive cusps and 

 exhibit a reduction of the metacone in favor of the paracone ; ""3 

 is the smallest of the series and has lost the nietacone entirely. 

 The lower incisors are reduced to two small teeth in each ramus. P^ 

 is small and single rooted, separated from the canine by a short space; 

 p2 aiidT^ are larger and have a well developed cutting talon, while p* 

 is the largest of the series and rendered completely molariform by 

 the addition of a paraconid. The molars differ from those of Dis- 

 sacusm the entire absence of the metaconid, or perhaps it would be 

 more correct to say that it has become completely fused with the 

 protoconid. The skull has a very long cranium and short face, the 

 zygomatic arches are extremely long, massive and widely expanded. 

 The mandible has a slender liorizontal ramus and extremely broad 

 ascending ramus, ending in a bluntly rounded and slightly everted 

 coronoid ; the angle is truncate and not continued into a distinct 

 process; the symphysis is unusually long. The limb-bones of this 

 genus, as described by Cope, show a remarkable disproportion between 

 the length of the fore and hind legs. The humerus is very short and 

 stout, with a very prominent deltoid crest, which extends nearly the 

 whole length of the shaft; there is no distinct intertrochlear promi- 

 nence; the entepicondyle is very prominent and pierced by a fora- 

 men. The ulna is long in proportion to the humerus and has a 

 strikingly long olecranon. The radius has a transversely oval head 

 and massive distal end. The femur is long and stout, the tibia long 

 and rather slender. The astragalus is well grooved and has a large 

 cuboidal facet which is nearly half as wide as that for the navicular, 

 a character unknown among creodonts, except in this family. The 

 metapodials are short, the phalanges depressed, the unguals flat- 

 tened and almost hoof-like. 



The species of this group were the largest of the Eocene flesh- 

 eaters and must have presented an exceedingly curious appearance 

 when in life from the disproportion between the great head, exceed- 

 ing that of the largest grizzly bears in size, and the small weak feet, 

 as well as that between the length of the fore and hind limbs. 



Two species : P. {Mesonyx) ossifraga Cope and P. gigavtea Osborn. 

 "Wasatch. 



