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University of California Publications in Geology [Vol. 9 



it has been possible to reach interpretations of new Pacific Coast col- 

 lections which would otherwise have been attained with difficulty. 

 Material assistance in study of the PUohippus group was also given 

 by Professor Richard S. Lull of Yale University through preparation 

 of excellent casts representing the dentition and feet of the type speci- 

 men of PUohippus pernix. It is with pleasure that the writer acknowl- 

 edges the co-operation of those who have contributed to the furtherance 

 of this and of other related investigations. It is presumably not an 

 exaggeration to state that, at this stage in the advance of science, there 

 can be little hope of material progress in new work without such co- 

 operation as tends to make the individual investigator merely one 

 among many assisting in the advance movement in a given direction. 



PLIOHIPPUS PBOVEBSUS, n. sp. 

 Equus or PUohippus, sp. Merriam, J. C, Trans. Amer. Phil. Soc, n. s., 



vol. 22, part 3, p. 33, 1915. 

 Equus or PUohippus, probably new. Merriam, J. C, Univ. Calif. Publ. 

 Bull. Dept. Geol., vol. 9, p. 56, 1915. 

 Type specimen an upper cheek-tooth, M 1 or M 2 , no. 21330, from the upper 

 portion of the Etehegoin formation, locality 2079, North Coalinga region, western 

 border of the San Joaquin Valley, California. 



Cheek-teeth large, long-crowned, heavily cemented. Upper cheek-teeth 

 slightly curved; mesostyle heavy; fossettes wide to narrow, with moderately 

 crinkled enamel borders; protocone large, strongly compressed laterally in the 

 molars, inner border convex or nearly flat. Lower cheek-teeth with short or 

 long parastylid; metaconid-metastylid column commonly long anteroposteriorly 

 and narrow transversely, inner groove wide, flat as in Equus, or somewhat nar- 

 rowed tending toward the angular form seen in PUohippus; outer faces of 

 protoconid and hypoconid either convex or somewhat flattened. 



Limb elements, so far as known, much like those of Equus. Unciform facet 

 of metacarpal III sloping away from the plane of the magnum at approximately 

 the angle shown in Equus. Lateral digits apparently much reduced distally and 

 feet presumably monodactyle. 



As indicated in earlier publications, 2 the advanced equid of the 

 upper Etehegoin finds its nearest American relatives in Equus {PUo- 

 hippus) simplicidens 3 and Equus (PUohippus) cumminsii of the 

 Blanco Pliocene in Texas. Like the California species the two Texas 

 forms are known by very imperfect material in which the lower denti- 

 tion furnishes the better representation. The Blanco species were con- 

 sidered by Cope 4 to represent ancient types of the Equus group with 



2 Merriam, J. C, op. cit., 1915. 



3 Bef erred to Equus by E. D. Cope (Geol. Surv. Texas, 4th Ann. Bep. for 

 1893, p. 66); but considered as PUohippus by J. W. Gidley (Bull. Amer. Mus. 

 Nat. Hist., vol. 14, p. 123, 1901). 



■» Cope, E. D., Proc. Amer. Phil. Soc, vol. 30, p. 125, 1892. 



