PARAHIPPUS. 



79 



high and narrow. (3) In upper incisors a deep pit entirely surrounded by raised internal cingulum; (4) canine alveolus 

 small [possibly a female]; (5) parastyle and mesostyle less prominent than in P. nebrascencis ; (6) vestigial cingulum on 

 protoloph; (7) protocone and protoconules separated by a narrow constriction; (8) metalophs of p^m 3 exhibit small 

 crochet; (9) metalophs not uniting, thus pli crochet not entirely isolated; (10) hypostyle strong, notched posteriorly; 

 (11) pit in lower incisors resembling a groove; (12) pi diminutive, p2-m3 with well marked external cingulum terminat- 

 ing in a diminutive hypoconulid; (13) heel of 1113 moderate in size; (14) no indication of cement. 



Referred specimens. — (Matthew, 1913) From the Lower Harrison a crushed skull, jaws, and greater part of skeleton, 

 Amer. Mus. 13769, and upper jaws, Amer. Mus. 13767, are referred to this species. These specimens agree with Loomis's 

 type in the following characters: (1) teeth moderately brachyodont; (2) crochet absent on p 2 ~ 3 , small and simple on other 

 grinding teeth; (3) premolars relatively small, scarcely exceeding m 1 " 3 in length and distinctly less in width; (4) small 

 canines in type, a female character, large canines in Amer. Mus. 13769, a male character. (5) Length of skull, occiput 

 to incisors, .341. (6) Length of Mtc. Ill .181; (7) Mtc. V a nodule instead of a short splint. (8) Nearest affinities with 

 the relatively large, massively proportioned, brachyodont P. nebrascencis group. 



MERYCOCHGERUS-PARAHIPPUS ZONE. 8. LOWER MIOCENE. 



This zone is typified by the Upper Harrison of western Nebraska and the Upper Rosebud of South Dakota. 

 It also extends into northeastern Colorado, into Wyoming, Texas, and Montana The horses belong 



TO THE GENUS PaRAHIPPVS, NOW ATTAINING LARGE SIZE, AND BEGINNING TO APPROXIMATE THE MlDDLE MlOCENE 

 STAGES. 



Parahippus nebrascensis Peterson 1907. 

 Text Fig. 55. 



Parahippus nebrascensis sp. nov., Peterson, O. A. "The Miocene Beds of Western Nebraska and Eastern Wyoming and their 

 Vertebrate Faunae," Ann. Carnegie Mus., Vol. IV, No. II, July, 1907, pp. 57-60, PI. xix. 



Horizon and locality. — " Upper Harrison beds on Niobrara River, in Sioux County, Nebraska." Merycochoerus zone. 

 Collected by O. A. Peterson. 



Type. — Carnegie Mus. 1440. (Peterson) "This species is based on a skull with the left mandible practically com- 

 plete, the pelvis, the right femur, tibia, calcaneum, astragalus, and the proximal end of a metapodial of one individual." 

 Measurements: (Peterson) occiput to incisors .370; length of p L m 3 .222; p 1-4 .072; m 1-3 .064. 



Type figure. — Text Fig. 55 of this Memoir. 



Characters. — (Peterson, 1907) (1) An animal of large size. (2) Premolars of proportionately large size when com- 

 pared with molars, p 2 the longest tooth of premolar series ; (3 ) protostyle of p 2 unusually well developed ; (4) posterointernal 

 tubercle of m 2 [hypostyle] more highly developed than in P. texanus. (5) Lachrymal fossa plainly indicated; (6) anterior 

 border of orbit opposite anterior portion of m 3 ; (7) orbit closed posteriorly. 



(Osborn, 191S) (1) Hypostyle of molars and premolars subtriangular ; (2) crochet developed on metaloph of p 4 , m 3 ; 

 (3) metaloph uniting throughout grinding series, p 2 -m 3 , with ectoloph; (4) dentition brachyodont, robust. 



(Matthew, 1913) Referred upper and lower jaws, Amer. Mus. 12924, from the Upper Rosebud, agree very closely 

 with Peterson's type, being only slightly inferior in detailed measurements. 



Parahippus pawniensis atavus subsp. nov. 



Plates 38, 39.9,13. Text Fig. 56. 



Horizon and locality. — Upper Harrison formation, near Agate, western Nebraska, Merycochoerus zone. Type col- 

 lected by American Museum Expedition of 1908. 



