158 



osborn: OLIGOCENE, MIOCENE, pliocene equid^e. 



lower fossa [maxillary]; (5) infraorbital foramen above anterior border of m 1 ; (6) anterior border of orbit above posterior 

 border of m 3 . (7) Grinding faces of the molar crowns wider than long; (8) protocone large and well fused, projecting more 

 prominently inward than the hypocone, which is not distinct in any of the teeth; (9) enamel borders perfectly simple, with 

 no loop between the protocone and hypocone. (Gidley, 1907, p. 915) (10) Its general skull characters more nearly approach 

 those of Protohippus pcrditus as that species is now understood, especially in the form and position of the lachrymal fossa, 

 also in the presence of a deep depression on the upper surface of the skull in the median line directly between the orbits, 

 as in P. pcrditus; (11) it also agrees with P. pcrditus in the unusual broadening of the nasals anteriorly; (12) the com- 

 parative shortness of the preorbital region; (13) the deep constriction of the preorbital region immediately in front of the 

 premolars. A distinction is (14) the presence of an incipient malar fossa, and the greater depth of the lachrymal fossa. 

 (Osborn, 1918) (15) Grinding teeth deeply worn, all enamel foldings obliterated; (16) extreme transverse diameter due to 

 the basal section of the crown; (17) protocone prominent, constricted; (IS) hypocone region somewhat less prominent, 

 unconstricted. 



Pliohippus interpolatus Cope 1893. 

 Plates 24.0, 25.13. Text Fig. 120. 



Hippidium interpolation, Cope, Cope, E. D. "A Preliminary Report on the Vertebrate Paleontology of the Llano Estacado," 

 Fourth Ann. Rept. Geol. Surv. Texas (1892) 1893, pp. 42-43, PI. xii, figs. 3, 3a, 4. 



Fig. 126. Original figures of the type of Pliohippus interpolatus Cope, Univ. Texas Coll. (cast Am. Mus. 14387). 



(3) Grinding face of m 2 ; {3a) posterior view of crown of m 2 ; (4) grinding face of supposed m 1 . Natural size. After Cope, 

 1893, PI. xii, figs. 3-4. 



Horizon and locality. — Mulberry Canon, near Goodnight, Texas, "Goodnight beds," Clarendon formation, Upper 

 Miocene. Type collected by Mr. W. F. Cummins, (p. 40) "near Goodnight's on the Staked plain." 



Type. — Univ. Texas Coll. (cast Am. Mus. 143S7). (Cope) "Established on two right superior molars, prob- 

 ably derived from the same animal. They are apparently the first and second true molars." Measurements: (Cope, 

 p. 42) m 1 a.p. .028, tr. .027; m 2 a.p. .029, tr. .0295, height of crown .085. 



Type figure. — Text Fig. 126 of this Memoir. 



Characters. — (Cope, 1893, Osborn, 1918) (1) Distinguished from corresponding teeth of Protohippus by the small 

 size of protocone and hypocone; (2) protocone uniting with protoconule; (3) a pli caballin and crochet fold in prefossette, 



(4) single enamel fold in postfossette; (5) hypostyle region simple, fossettes relatively large, borders relatively simple; 

 ((i) crowns curved transversely but not anteroposteriorly ; (7) cement abundant, 



Giclley observes (1907, p. 917) (1) that the type molars are of a young adult individual, hence the fossettes are 



