FAUNA OF THE EQUUS BEDS. 



79 



part preserved are about equal to those of the M. robustus, Owen, from 

 Argentina. The transverse extent of the condyle is about 210 Mm. (re- 

 stored), of which the popliteal fossa is about 60 mm. 



Since the species was described, I have received from Mr. George 

 Duncan, of Paisley, Oregon, an imperfect symphysis mandibuli from 

 near the original source of the M. sodalis, which presents characters ap- 

 propriate to that genus and species. It is accompanied by a symphysis 

 of a large peccary, the first found in that horizon and locality. 



PROBOSCIDIA. 



ELEPHAS, Linn. 

 ELEPHAS PKIMIGENIUS, Blum. 



Remains of this species are quite abundant in the Equus beds of the 

 Staked Plains and neighborhood, but are generally in a fragmentary 

 condition. The teeth from Rock creek are neither thick plated nor thin 

 plated, but are much as in the typical variety of E. primigenius , and some 

 plates are slightly crenate, while others are plain. 



DIPLARTHRA. 



EQUUS, Linn. 



As elsewhere in the Equus beds, several species of true horse occur, 

 and they are represented by numerous specimens of all parts of the 

 skeleton. No entire skeleton has been found, and until this is done it 

 will be impossible to associate positively the bones with the appropriate 

 dentition. The superior molars may be distinguished as follows: 



a. Smaller species; molars 25X25± mm. 



Enamel borders, simple IS. tau. 



Enamel borders, complicated at middle of crown E. semipUcatus. 



aa. Larger species; molars 30X35± mm. 



Enamel borders, a little folded at middle of crown E. excelsus. 



Enamel plates much complicated on both anterior and pos- 

 terior lake borders E. major. 



EQUUS TAU, Owen. 



Philos. Trans. Royal Soc, 1869, p. 565; Equus barcencei, Cope, Pro- 

 ceeds. Amer. Philos. Society, 1884, p. 15. 



A single superior molar from Tule Canyon. This tooth is perfectly 

 straight, and presents very simple enamel borders, and the anterior lake 

 has an imperfect loop. The crown is slightly curved, both transversely 

 and posteriorly. I have already indicated this species from beds near 

 San Diego, in southwest Texas. 



