258 



DOUGLASS — FOSSIL MAMMALIA 



toconid. The deuteroconid is only represented by a narrow ridge passing part way down 

 the tooth inward and backward from the, apex of the protoconid. The metaconid is 

 much better developed and is represented by a posterior tubercle, connected by a narrow 

 ridge with the apex of the protoconid. 



In P T the paraconid is thicker and higher than in P ¥ , and is inflected inward. The 

 other four elements — the protoconid, metaconid, deuteroconid and tetartoconid* — are all 

 well developed and surround a quadrangular cup-shaped depression. This is true also 

 of Oreoclon and Eucrotaphus, and the form of the tooth differs very little from these. 

 In this particular tooth, however, the posterior depression would, on further wear, make 

 an islet, not an enamel loop. It is shallow and would entirely disappear if there should 

 be much wear. The great difference between this tooth and the corresponding ones of 

 the above-named genera is in the narrowness of the tooth as compared with its length. 

 I\ also differs in this respect and they are, therefore, more like Merycochosrun (?). P ;V 

 differs from that of Oreoclon oulbertsoni in the simplicity of the inner ridges— rudimen- 

 tary deuteroconid — in this respect being much like the specimen I have examined of 0. 

 gracilis. It also differs in having the paraconid partly separated from the protoconid. 

 Ao-ain in these slight variations the differences are in the direction of Merycoohosrus (?) . 

 In the type of M. (?) altiramm, which I have described from the Loup Fork of Mon- 

 tana, the teeth are little worn and give an excellent opportunity for comparison (1901, p. 

 73, Fig. 1). The present species shows almost no advance on this pattern. The para- 

 conid on the last two premolars is a little thicker, and this element is distinguishable on 

 P- 2 -, which has just begun to develop the posterior elements. The teeth have all increased 



in height. 



Specimen No. 66. — In this specimen the mental foramina are farther apart. The 

 anterior one is under the anterior part of P., and the posterior one under the anterior of 

 P T . There is a thickening of the ramus — an outer convexity between these two foramina 

 — not seen in No. 48. 



P-2- is shorter than P., and the roots are not close together as in the oilier specimen 

 P T is about the same. P ¥ has the metaconid and tetartoconid much lower and they are 

 not united at the posterior inner angle of the tooth, so that after considerable wear there 

 would still be an opening to the inner basin as in Oreoclon and Meryeoehmrm (?). P-g- 

 and Py are broader than in No. 48. 



M T is shorter than P T . The posterior pair of crescents is wider than the anterior 

 pair. The outer crescents are short antero-posteriorly. 



I will propose for the specific name P. alpha, with No. 48 as the type specimen, 



*The tetartoconid in small. 



