142 



University of California Publications. 



[Geology 



The long, dagger-shaped canines resemble those of a carnivore, 

 and are quite unlike the corresponding teeth in any other known 

 species of Mesohippus. The edges developed anteriorly and pos- 

 teriorly are sharply set off from the rest of the tooth crown. 

 The tips are unworn. A large hypostyle is present on all the 

 molars and molariform premolars. On all except M 3 it gives off 

 a narrow spur-like cmgulum which borders the hypocone pos- 

 teriorly. On most of the molars and premolars there are one 

 or more small tubeix-les at the mouth of the transverse valley. 

 No other traces of an internal cingulum are seen. The external 

 cingulum is not continued across the bases of the styles. 



The cranium lacks the bones investing the posterior portion 

 of the brain case and has been somewhat crushed, accentuating 

 the flatness of the forehead. The orbit is almost completely closed 

 by the strongly developed postorbital process of the frontal. The 

 supraorbital notch is entirely encircled by bone, forming a large 

 foramen. There is a well marked preorbital fossa. 



With the cranium were preserved portions of the left scap- 

 ula, humerus and radius. Only the glenoid portion of the scap- 

 ula is represented. It agrees with M. bairdi as described by 

 Scott,* except that the free border of the coracoid process is bent 

 inward, forming a rather open hook. The humerus is without a 

 supratrochlear foramen. In this respect it differs from M. bairdi 

 in which the anconeal fossa is perforate. The radius, of which 

 the proximal portion is preserved, is very much like that of M. 

 bairdi. 



The specific name refers to the sharp pointed canine teeth. 



The new species may be readily distinguished from the horses 

 of the Middle and Upper White River by the dental measure- 

 ments, the great length of the canine and the character of the 

 orbital region. It approximates in dimensions M. br achy stylus 

 Osbornt from the Leptauchenia beds, but differs from that 

 species in the shape of M 3 , the form of the postorbital process 

 and the closure of the supraorbital notch. $ 



* Osteology of Mesohippus and Leptomeryx. Jour, of Morphology, 

 Vol. V, No. 3, p. 319. 



t New Oligocene Horses. Bull. Am. Mus. Nat. Hist., Vol. XX, pp. 

 167-179, 1904. 



+ Compare PI. 18 with Osborn, op. cit. PI. V, E. 



