Marsh Collection, Peabody Museum. 285 



the suborder thus far known. I define the five families as 

 follows : 



Oxyclcenidce. No specialized carnassials ; tritubercular upper 

 and lower molars; shear rudimentary or absent (Matthew). 



Genera : Oxyckenus, Chriacus, Protochriacus, Deltatherium, 

 and Tricentes. All from Lower and Middle Eocene. 



Arctocyonidce. No carnassials ; molars flat-crowned ; pre- 

 molars becoming progressively reduced in size ; scaphoid and 

 centrale early united; hallux and pollex more or less opposable; 

 claws compressed, curved, and pointed. 



Genera : Arctocyon, Clcenodon, and Anacodon. From Lower 

 and Middle Eocene. 



31esonychidce. No carnassials ; molars with characteristic, 

 high, bluntly conical cusps, superior tritubercular, inferior becom- 

 ing premolariform ; claws depressed, little curved, and fissured ; 

 limbs in later forms becoming much modified in accordance with 

 running habit. 



Genera: Triisodon, Goniacodon, Sarcothraustes, Dissacus, 

 Pachycena, Mesonyx, Dromocyon, and Ilarpagolestes. .From 

 Lower, Middle, and Upper Eocene. 



Oxycenidce. PmA and M. T * ¥ carnassial, of which M.-J are 

 largest and most specialized ; claws, as far as known, depressed, 

 little curved, and fissured. 



Genera: Oxycena, Patriofelis, Limnocyon, Oxycenodon, and 

 There ctherium. From Middle and Upper Eocene. 



Hycenodontidw. Pm> and M.^^ carnassial, of which M.| are 

 the most specialized, especially in the later types; claws depressed, 

 little curved, and fissured ; or compressed, curved, and pointed ; 

 in early types a double condyloid foramen as in Marsupials. 



Genera: Sinopa, Proviverra, Hycenodon, Pterodon, Quercy- 

 therium, Cynohycenodon, Paheos?'?iopa, and Didelphodus. From 

 Middle and Upper Eocene and Oligocene. 



Family Mesonychidce Cope. 



This family is represented at the very beginning of the 

 Tertiary by the genus Triisodon, with three well-marked 

 species from the Puerco of New Mexico. In the succeeding 

 Torrejon beds of the same region, three generic modifications 

 make their appearance ; namely, /Sarcothraustes, Goniacodon, 

 and Dissacus. The first of these has been properly regarded 

 as the direct descendant of Triisodon, while the last repre- 

 sents the beginning of the Mesonyx line of succession. The 

 first three of these genera — Triisodon, Sarcothraustes, and 

 Goniacodon — have been considered by Cope and Scott to rep- 

 resent a distinct family. Triisoclontidee, but I have shown* that 

 their classification is probably best accomplished by placing 



* Bull. Amer. Mus. Xat. Hist, June, 1899, p. 146. 



