VERTEBRATE FAUNA OP THE LOUP FORK BEDS. 39 



As already indicated, this siDecies is of about the dimensions of the P. 

 gracilis so far as preserved, but differs widely from this and from other 

 species in the slender form of the mandibular rami. The vertical diame- 

 ter of the latter is about half of that characteristic of the P. gracilis. 

 The postorbital region is also more elongate. 



BLASTOMERYX, Cope. 



Report U. S. G. G. Surveys west of 100th meridian, IV, 1877, p. 350; 

 American Naturalist, 1889, p. 125. 



BLASTOMERYX GEMMIFER, CopC. 



Op. cit., p. 360, pi. LXXXII, fig. 13 (Dicrocerus). Merycodusgem- 

 mifer, Cope, Ann. Report U. S. Geol. Survey of Terrs., 1873 (1874), 

 p. 531 partim. 



Parts of two individuals represent this species. The most important 

 specimens include the posterior four molars of the right side, the P. m. i. 

 and M. i fixed in a portion of the maxillary bone, and a pax't of the 

 right ramus mandibuli with the posterior four molars in place. The sec- 

 ond individual is a little larger than the first, and includes the left infe- 

 rior M. i and a part of the left inferior M. iii. All these teeth were 

 found by myself, lying close together. 



As the characters of this species are little known, I give an account of 

 these teeth. The molars are all moderately brachydont, with the basal 

 shoulders visible on the alveolar border. The superior molars are with- 

 out styloid tubercles between the bases of the internal columns, while 

 they are present in all the inferior true molars. In this respect the supe- 

 rior molars differ from those of the larger B. borealis, Cope, where the 

 stylets are present. The crowns of the superior molars contract rapidly 

 transversely to the apex. The anterior and posterior bounding vertical 

 ridges of the metacone are prominent and there is no median crest. The 

 paracone presents a strong anterior bounding ridge and a strong median 

 ridge; all as in the B. borealis. No cingulum. The first premolar is small, 

 and its external border marks the anterior lake of the first true molar. 

 The external face is concave on the anterior half. The part of the exte- 

 rior wall anterior to this concavity is protocone, and it sends a process 

 inward towards the internal crescent. Posterior to this process, the ex- 

 terior wall is apparently tritocone,* and it is convex on the inner side. 

 The internal crescent or deuterocone is regular; and extends transversely 

 in front anterior to the protocone, from which it is separated by a notch. 

 Above (below) this notch the protocone presents an external ridge ; prox- 

 "imad there is no ridge. No cingula. 



* See Scott ou IST omenclature of Premolar Cusps, in American Journal of Morph- 

 ology, 1891, p. 49. 



