HIPPARION. 



199 



posteriorly, oval in section, with inner and outer borders convex; (5) anterior and posterior borders of both pre- and post- 

 fossettes doubly or triply plicate, prominent crochet and pli caballin folds; (6) prominent para- and mesostyles; (7) 

 enamel plication resembling that of H. venustum, which is of similar dimensions but differs in the protocone section. 

 (Gidley, 1907) (8) Type agrees very closely with that of //. montezuma Leidy; (9) the type a true molar, somewhat smaller 

 than that of H. montezuma, which is a premolar, the difference in size such as might exist between molar and premolar 

 teeth of one individual; (10) localities from which the types were obtained not widely separated. 

 This type is regarded by Gidley (1907) as probably identical with H. montezuma Leidy. 



Hipparion rectidens Cope 1SS6. 

 Text Fig. 164. 



Hippotherium rectidens, sp. nov., Cope, Edw. D. "On Two New Species of Three-toed Horses from the Upper Miocene, with 

 Notes on the Fauna of the Ticholeptus Beds," Proc. Amer. Philos. Soc, Vol. XXIII, 1886 (sig. dated Apr. 15, 1886), pp. 360-361, no 

 figure. "A Review of the North American Species of Hippotherium," Vol. XXVI, 1889 (sig. dated June 1, 1889), pp. 435, 458, figs. 3, 3a. 



Fig. 164. Type of Hipparion rectidens Cope, Am. Mus. Cope Coll. 8346. (Left) Original figures of the type; 3 

 lateral view, 3a crown view. After Cope, 1889. (Three right-hand figures) Type tooth redrawn under the direction of 

 Osborn; crown, (a) external, and (b) anterior views. All figures natural size. 



Horizon and locality. — (Cope, 1886) Loup Fork, Upper Miocene formation of Tehuichila, Vera Cruz, Mexico. 

 Type collected by Dr. Santiago Bernard. Probably Upper Miocene. 



Type. — Am. Mus. 8346 (Gidley, 1907) An upper ? premolar of the right side. Measurements : (Cope, 1886) diame- 

 ters of crown, a.p. .0215, tr. .0215, length of crown .045. 



Type figure. — Text Fig. 164 of this Memoir. 



Characters. — (Cope, 1886) (1) Enamel folds similar to those of the type of H. peninsulatum from the same locality; 

 (2) including the subquadrate central loop [protocone], which is nearly cut off from the anterior lake [prefossette], tooth 

 differing from H. peninsulatum in its larger size, presenting 6% more area of grinding surface; (3) shaft of tooth straight 

 instead of being strongly curved; (4) crown owing to wear nearly square, while it is oblong in the type of H. peninsulatum; 

 (5) two large loops extend inward toward the column instead of one [i. e. double pli caballin]. 



