42 GEOLOGICAL SURVEY OF TEXAS. 



relictwm, Cope, from the Pliocene of Oregon, is of approximately the 

 same geologic age, but tliis is a true Hippotherium, and the column (pro- 

 tocone) lias an oval section. 



Another species of Protohippus was found by Mr. Cummins at the same 

 localit3'. As it is represented by only an uncharacteristic superior molar, 

 I do not attempt its identification. 



PROTOHIPPUS PERDiTus, Lcidy. 



A single right superior molar, moderately worn, presents no tangible 

 differences when compared with corresponding teeth of P. perditus from 

 the Loup Fork beds of Colorado. I nevertheless refer the animal to this 

 species provisionally, as I can not prove that it is not a species of Hip- 

 pidium. 



HIPPIDIUM INTERPOLATUM, Cope. 



Sp. nov. Plate XII, Figures 3, 4. 



Established on two right superior molars, probably derived from the 

 same animal. They are apparently the first and second true molars. The 

 form and area of the grinding surfaces are similar to those of the cor- 

 responding molars of the domesticated horse (Equus caballus). They 

 may be distinguished from the corresponding teeth of the species of Pro- 

 tohippus by the small size of the protocone and hypocone. The former 

 reached posteriorly to the line of the anterior border of the posterior 

 lake, but does not overlap it, as is the case with the species^of three-toed 

 horses generally. Its junction with the paraconule is strongly constricted. 

 The internal enamel border between the protocone and hypocone is in- 

 flected to a point beyond the line of the internal border of the interior 

 lake, and in front of its apex it sends inward a deep narrow loop. The 

 lakes are relatively large, and the borders are quite simple. The anterior 

 border of the anterior lake is simple; the posterior border has an inflec- 

 tion but no loop. The exterior border of the posterior lake has one in- 

 flection, and its posterior border a slight emargination. Owing to the 

 transverse width of the lakes, their bones are little produced. The 

 crowns are curved transversely, but scarcely anteroposteriorly. Ce- 

 mentum abundant. Roots very short. 



Measurement. 



Mm. 



Diameters of grinding face of M. 1 i anteroposterior 28 



( transverse 27 



Diameters grinding face of M. ii \ anteroposterior 29 



( transverse 29 . 5 



Length of crown of M. ii 65 



The crowns are sufficiently worn to present the character of maturity. 



