M. R. Thorpe— Arceocy on. 375 



the Felida?, such, for instance as the possession of the 

 large M 2 which none of the post-Middle Oligocene f elids 

 retained. The first lower molar is not at all cat-like in 

 structure, and the slenderness and general characters of 

 the ramus all point to an origin not in the felid phylum. 

 The evidence, however, does point unmistakably toward 

 the dog-like phyla. 



While it is stated above that there are no closely com- 

 parable American forms so far known, yet we might point 

 out the essential differences and show wherein Arceocyon 

 could have been derived from some autochthonous genus. 



In the first place, the heel of the lower carnassial is 

 trenchant, for the hypoconid is about medially situated 

 on the talonid. This is also true of Simocyon primigen- 

 ius, as shown in a very good cast (Cat. No. 11649, Y. 

 P. M.) of the type. Therefore we must place them in the 

 group which parallels the more typical canoid line of 

 descent, namely, the assemblage of forms to which belong 

 Daphceniis, Temnocyon, Enhydrocyon, Iscliyrocyon, and 

 others up to and including the recent genera, Cyon, 

 Icticyon, and Lycaon. Osborn has placed Simocyon also 

 in the Dhole-like group, and Arceocyon should likewise be 

 classified under this head. 



If Arceocyon is an autochthonous form, then Daplicenus 

 and Temnocyon are most probably in the direct line of 

 ancestry, while Enliydrocyon is apparently an aberrant 

 side branch with which we are not at present concerned. 



In the Upper Miocene (Loup Fork beds) there is a 

 peculiar genus, Iscliyrocyon, which is here provisionally 

 placed in this group on account of the trenchant heels 

 of the first two lower molars. The large size of the 

 molars and the absence of the metaconids upon them 

 show that it is, however, far removed from the large 

 majority of the other known genera of the Canidae, and 

 especially so from Arceocyon. It probably represents 

 another of the various aberrant forms in the canid 

 phylum. According to Doctor Matthew, the general pro- 

 portions suggest Amphicyon and Dinocyon. 



In the later epochs, Pliocene and Pleistocene, of North 

 America, we find more nearly contemporaneous forms, 

 but if we examine them in detail we see that the similar- 

 ities are more apparent than real. In these later forma- 

 tions there are various more or less hyaanoid Canidae, 



