VERTEBRATE FAUNA OF THE LOUP FORK BEDS. 45 



further off, but is strongly recurved, forming a prominent narrow ridge 

 bounding the inner side of the ci'own posteriorly. In the three other 

 specimens (2, 3, 4) it is not pi-ominent, and is separated from the meta- 

 stylid by a rather flat gutter, as in E. minutus. Three of the crowns, in- 

 cluding tlie type, are curved anteroposteriorly; the one with the strong 

 bounding ridge is straight. None are curved transversely. All are 

 "wider anteroposteriorly at the grinding face than at the root, a differ- 

 ence most observed on the least worn crown. Cementum is present on 

 the internal face near the grinding surface only; on the external face a 

 thin layer extends nearly to the base. The anterior and posterior faces 

 are naked. 



Measurements . 



Mm. 



( longitudinal 55 



Diameters No. 2 , J anteroposterior 24 



( transverse 10 



i longitudinal 40 



anteroposterior 22 



transverse 12 



As compared with this species th.eE. minutus differs as follows: (1) In 

 the convex protoconid and hypoconid; (2) in the absence of external 

 median keel (loop); (3) in the absence of an anterior marginal bounding 

 ridge of the external side of the crown; (4) in the inferior size. The E. 

 minutus is undoubtedly from the Blanco bed, and may be the direct 

 descendant of the E. eurystylus. 



SYNOPSIS OF SPECIES. 



Mr. Cummins found in the bed above the gravel which overlies the 

 Loup Fork formation, the following species: 



Aphelops, sp. 



Protohippus lenticularis, Cope. 



Protohippus, sp. No. 2. 



Protohippus fperditus, Leidy. 



Hippidium interpolatum, Cope. 



Hippidium fspectans, Cope. 



Equus eurystylus, Cope. 



Equus fsimplicidens, Cope. 



As already remarked, the genera Aphelops and Protohippus are char- 

 acteristic of the Loup Fork beds, but are not known to extend higher. 

 Equus, on the contrary, has never been found in the Loup Fork forma- 

 tion, but is the only genus of horses found in the Blanco and Equus ter- 

 ranes. Hippidium is said to be derived from the Loup Fork beds of 

 Kansas and Nebraska, but I have never found it in place. It is likely 



