CREODONTA. 



257 



Fig. 7. 



Fig. 8. 



It is possible that the genus Diacodon Cope belongs here also; its species 

 resemble some Marsupialia in the inferior dentition, and are of small size. 



The genus Mesonyx* which I discovered in the 

 Bridger beds of Wyoming, has the trochlear face of 

 its astragalus completely grooved above as in the 

 true Carnivora, and its distal end presents two dis- 

 tinct facets, one for the cuboid and the other for the 

 b navicular bones. It represents on this account a 

 peculiar family, the Mesonychidce. 



There are various degrees of development of the 



sectorial structure of the molars in this suborder. In 



' some of them, as Didymictis, only one of the inferior 



molars presents this structure ; in othei's two, and 



In one type, the last superior molar 



Fig. 7. Distal extremity of 



tibia of Amhhjclonus xinimus jj^ otllCrS three, 

 Cope. Fig. y. Distal cx- 



treniity of tibia of or^ffna IS lougitudinal ; in others, it is transverse. In Arc- 



thirds natural size. From 

 Report Expl. and Surv. W. 

 of lOOth Mer., G. M.Wheeler, 



tocyon the superior true molars are tubercular. 



The glenoid cavity of the squamosal bone pre- 

 ivj pt. ii. sents differences in the various genera of this sub- 



order. In Arctocyonidcc (fide De Blainville), Oxycenidce, and Mesonychidce it 

 is bounded by a transverse crest anteriorly, as well as by the postglenoid 



Fig. 9. posteriorly, while in the 



Leptictidce it is plane 



3 



and open anteriorly. In 

 * Amhlyctonidce. its con- 



1 dition is unknown. In 



2 existing Carnivora this 

 chai-acter is not very 

 constant as a family 



Fig. 9. Portions of maxillary and mandibular bones of Oxydiim Zii^iHa UeiinitlOn ; it IS DCSt 

 Cope, one-half natural size; a, maxillary bone from below; b, last Azt^A *n t]iA VcJirl 



superior molar. From Report Expl. Surv. W. 100th Mer., G. M. 



Wheeler, vol. iv, pt. ii. and least marked in the 



Canidce. Nevertheless there is a group of genera allied to the OxycenidcB, 

 which are very marsupial in character, which have been called the Leptic- 



* Annual Report U. S. Geol. Surv. Terrs., ltJ72, p. 550. 



