530 



University of California Publications in Geology 



[Vol. 9 



anteroposterior^ and the internal groove is broad and flat. The 

 width and flatness of the groove sometimes considerably exceed that 

 in the simpler variations of Equus. In other lower cheek-teeth from 

 the upper Etchegoin (figs. 8, 9, and 10) the inner groove of the 

 metaconid-metastylid column is sharper than in Equus and more 

 nearly resembles that in typical Pliohippus. 



The form of the lower cheek-teeth in P. proversus is close to that of 

 the Blanco material referred by Cope to P. simplicidens. The two 

 types may be specifically different, but they apparently represent a 

 group, which, as is shown in the upper cheek-teeth, appears separable 

 from Equus, and does not correspond closely to typical Pliohippus. 



11 



Figs. 11 and 12. Pliohippus proversus, n. sp. From the upper Etchegoin Plio- 

 cene of the North Coalinga region, California. Both figures one-half natural 

 size. 



Fig. 11. Left metacarpal III, no. 22318, anterior and proximal views. 

 Fig. 12. Astragalus, no. 22334. 



KELATIONSHIPS 



The horses referred to the Pliohippus proversus type from the 

 upper Etchegoin Pliocene of California are distinct from all of the 

 most advanced horses of the lower Etchegoin and Ricardo Pliocene 

 stages of the Pacific Coast province. There is, however, in certain 

 characters sufficiently close resemblance to some of the Ricardo species 

 to suggest that the upper Etchegoin form may be derived by modifica- 

 tion from one of the early Pliocene Pacific Coast species near Plio- 

 hippus tantalus or P. fairbanksi. 



