CREODONTA 609 
blade having a large inner cusp. The upper teeth closely resemble 
the molars of Dasywrus, while the lower molars are like the lower 
carnassial of Cynodictis and Viverra; and thus indicate how the 
Creodonts may have passed into the true Carnivores through the 
extinct Afiacide. 
Arctocyonide and Mesonychide.—The first of these families is 
represented by Arctocyon primevus, one of the oldest known Tertiary 
mammals, from the lowest Eocene beds of La Fere, department of 
Aisne, France, and also by other species from corresponding beds 
at Rheims. The dental formula is 7 3, ¢ 4, p an m 3. The upper 
molars (Fig. 279) are tritubercular, with an incipient postero- 
internal column (hypocone) ; 
the lower are quadrituber- 
cular; and the premolars 
simple. The typical species 
was of large size, but the 
two of which the teeth are 
figured were considerably Fic. 279.—The three right upper molars of Arcto- 
smaller. In the American cyon duelt (a), and the second of A. gervaisi (b); from 
Mesonyx the dental formula the Lowest Eocene of Rheims. pr, protocone ; pa, 
paracone ; me, metacone; hy, hypocone; ml, meta- 
was the typical one, the jaws conule; pl, paraconule. (From Osborn.) 
were comparatively short, the 
mandibular symphysis was elongated, the cheek-teeth were of 
simple structure, and resembled the premolars of many of the true 
Carnivora, and the astragalus had a grooved tibial surface and 
distinct distal facets for the cuboid and navicular, resembling in the 
latter respect the corresponding bone of a Perissodactyle Ungulate. 
The terminal phalanges had deeply fissured extremities, and are said 
to be more like those of Rodents than true Carnivores. A/esonyx 
ossifragus was larger than a Grizzly Bear. Amblyctonus, of the same 
deposits, differs by the smooth tibial face of the astragalus and the 
development of an anterior cusp to the lower molars. 
39 
