MIOHIPPUS. 



65 



Metaloph hardly interrupted by metaconule, sharply separated by a deep notch from the eetoloph. Protoloph with well 

 marked protoconule, united with eetoloph by a narrow sha[r]pe-edged ridge which widens in moderately worn teeth. 

 Parastyle broadly rounded except in M 3 where it is compressed antero-posteriorly. M 3 with metaloph s[h]orter than pro- 

 toloph (t. c, as 8.5 mm. : 12.3 mm.), producing almost a triangular outline for the tooth crown. Mesostyle sharply defined 

 and ribs broadly rounded and prominent. The measurements seem also to be characteristic." 



Additional characters — (Osborn, 1918) (1) Canines probably male; (2) a large hypostyle on p'-m 3 ; (3) m 3 giving off 

 a narrow spur-like cingulum which borders the hypocone posteriorly; (4) one or more small tubercles at entrance of medi- 

 vallum, no other traces of internal cingulum; (5) external cingulum not continued across the bases of the styles; (6) orbit 

 almost completely closed by a strongly developed postorbital process; (7) a well marked preorbital fossa; (8) differs 

 from M. brachystylus of the Leptauchenia zone in the form of the postorbital process and in the closure of the supraorbital 

 notch. 



Fig. 44. Miohippus acutidens Sinclair, Univ. Cal. Pal. Coll. 376. (Upper) Original figure of the cranium of the 

 type. After Sinclair, 1905, pi. 18. (Middle) Same view of type cranium drawn by B. Yoshihara under the direction of 

 Osborn. Both figures one-half natural size. (Lower) Superior grinding teeth of the type, p'-m 3 of the left side. 

 Natural size. 



Miohippus equinanus, sp. nov. 

 Plate 3.6. Text Fig. 45. 



Horizon and Locality. — Lower Rosebud formation, Promerycochcerus zone, Porcupine Creek, Pine Ridge, South 

 Dakota. Type collected by Albert Thomson, American Museum expedition of 1906. 



Type. — Amer. Mus. 12912. Upper jaws containing p'-m 3 of left side, p 1-3 of right side. Measurements: p L m 3 

 .072; ^.041; p 2 " 4 .0363; m 1 " 3 .031; p 4 a.p. .0113, tr. .0146; m 1 a.p. .0114, tr. .0145. 



