384 PROCEEDINGS OF THE ACADEMY OF [1896. 



circle. The apex of the triangle is in U. pristinus internal, and 

 it is split by a fissure which separates paraconid from metaconid. 

 In U. haplodon the paraconid is wanting. In this respect U. 

 pristinus more resembles the modern bears. I suspect that U. pris- 

 tinus is distinct from U. haplodon, but of the same group ; more 

 approaching the typical Ursi. It is of smaller size, about equaling 

 the grizzly. 



Ursns haplodon belongs to the American type of the Plistocene 

 and present ages, which is distinguished from the typical Ursi by 

 the greater development of the sectorial part of the first inferior 

 true molar. This is due to the more anteroposterior direction of the 

 paraconid, the larger size of the protoconid and the smaller size of 

 the metaconid. The tooth makes a sensible approach to that of 

 Hyctnarctos. To this group belong the following species, and they 

 diflfer in the following ways : 



I. Superior premolars crowded, overlapping. (South American.) 

 Large species ; U. ornatus Cuv., U. bonaerensis Gerv. 

 Smaller species ; U. brasiliensis Linn. 



II. Superior premolars uninterrupted, not overlapping. (Cali- 

 fornian.) 



Muzzle very short ; U. sirnus Cope. 



III. Superior premolars spaced. (E. N. America.) 



Muzzle moderate ; U. haplodon Cope. 



Where U. pristinus should be placed in this series can only be 

 ascertained by future discovery. The three species first named 

 are separated from Ursus under the name of Treniardus (Gerv- 

 Arctotherium Brav.), as the humerus exhibits an entepicondylar 

 foramen. It is not known whether the last two species possess this 

 character or not. 



A conspicuous character is common to the living Tremardus 

 oDiatus and Ursvs (J Tremardus) haplodon, which is not present in 

 Tremardus bonaerensis of the Pampean beds. There are two mas- 

 seteric fossae of the mandible, which are separated by a crest which 

 extends obliquely downward and backward from below the coro- 

 noid process. 



The size of the teeth of this species, as well as that of the jaws 

 preserved, exceed the average dimensions of the grizzly bear 

 {Ursus horribilis). U. haplodon was evidently one of the most 



