308 Bulletin Americcai Museutri of A'atural History, [^'ol. XXVII, 



(2) Orbitosphenoid not compressed dorsoventrally in the ^larsupial 

 fashion (p. 245). 



(3) Palate not strongly fenestrated. 



(4) Tympanic process of alisphenoid, if jn-esent, not forming a hollow 

 shell for the tympanic cavity. 



(5) Angle of lower jaw not sharply inflected. 



(6) Epipubic bones reduced or absent. 



(7) Astragalus with neck well develo})ed. 



(8) Dental formula 1^1^; ; milk dentition not reduced. 



GENETIC RELATIONS BETWEEN CREODONTA AND FISSIPEDIA. 



Constitution of the Creodonta. The suborder Creodonta includes several 

 diverse groups of chiefly Eocene Carnivora which have been divided by 

 Schlosser and by IMatthew (1901, pp. 1-38) into three groups. The first 

 of these, the Creodonta Primitiva, including only the Basal Eocene Oxy- 

 claenidte with more or less simple tritubercular molars, may possibly be Insec- 

 tivores (Matthew). The second group, the Creodonta Adaptiva, included 

 the Arctocyonidse, Miacidfe ("Viverravidjie") and Palseonictidse. In the 

 first two families the ungues were compressed and the fourth upper premolar 

 and first lower molar were not modified into carnassials. The third family, 

 the Palaeonictidfe, was removed from this group to the Fissipedia by Wort- 

 man because p* and n\ show an early stage in the carnassial modification.' 

 The third group was called Carnivora Inadaptiva - in reference to the 

 fact that they were definitely excluded from ancestry of the Fissipedia be- 

 cause the specialized carnassial, when present, was developed behind p*. 

 The ungual phalanges are flattened and fissured. The first family is the 

 Mesonychidte, an early Eocene cursorial side branch which parallels the 

 Artiodactyls in its foot structure. In this family p^ remained simple, the 

 upper molars were bluntly cusped, tritubercular, the lower molars com- 

 pressed and trenchant. The second and third families (Oxysenidse and 

 Hypenodontidse) seem to be more nearly related to each other than either are 

 to the Mesonychidie. These ])arallel the Felidje and Canidse or the Hyteni- 

 dsie respectively in general proportions, and develop their carnassials from 

 the teeth behind j^j, namely, from the true molars. 



The Miacidce as connecting the two suborders. The question of the 



1 Matthew also has recently (1909) removed Palceonictis from the "Adaptiv^a," which as 

 thus restricted he calls the "Eucreodi." 



- Matthew now distrilnites the Creodonta Inadaptiva under two sections: the "Acreodi," 

 including only the Mesonychidte. and the " Pseudocreodi " (forms with false carnassials), includ- 

 ing the Oxyjenidae (Oxywiia Patriofelis Palceonictii etc.) and the Hycenodontidae. 



