I 1 6 Bidletin American Museum of Natural History. [Vol. XIV, 



however, would seem to be scarcely a sufficient reason for unit- 

 ing them, as, in addition to this being a somewhat variable char- 

 acter, the type specimen of E. excelsus shows a deep notch in m-^ 

 and a slight though well marked one in m^. (The notch in m^ 

 is not shown in Leidy's figure of the type.) 



Professor Cope again separated these two species in 1884,^ con- 

 sidering them distinct (as he explained in Rept. Geolog. Surv, 

 Texas, 1893), on the untenable ground of the smaller size of the 

 protocone in E. occidentalis. Moreover the specimens upon 

 which Cope evidently relied for his characters of E. occidentalis 

 were taken from an entirely different locality and undoubtedly 

 belong to a species different from either of the two species under 

 discussion. 



(10) Equus pacificus Leidy. 



Type Locality. — Martinez, Contra Costa Co., California. 



Type. — Superior p^. 



Author''s description. — " The triluratiiig surface in its arrangement of the 

 enamel presents nothing strikingly different from that of the corresponding 

 tooth of the recent horse. As in this there is an inflection of the enamel at the 

 bottom of the principal internal valley, and in this respect and the le.ss simpli- 

 city of folding of the enamel islefs of the triturating surface differs from Equus 

 excelsus of the Niobrara and of California. The tooth probably represents an 

 extinct species, upwards of eighteen hands high. Its measurements are as 

 follows : 



Length along the outer median column to the origin of the fangs, 26 lines 

 56 mm.). Breadth of triturating surface fore and aft, i64 lines (35 mm.). 

 Thickness independent of cementum, 15 lines (32 mm.)." 



Without giving any reason for doing so, Leidy included this 

 species in his list of synonyms of E. occidentalis given in ' Fossil 

 Vertebrates,' 1873, p. 322. 



It seems altogether likely, however, since E. pacificus is so 

 much larger, as is indicated by the tooth measurements, and is 

 more complicated in enamel folding, that it is distinct from E. 

 occidentalis. This view is strengthened greatly by an examination 

 of the Equus teeth from the Silver Lake, Oregon, locality, which 

 were described by Cope and referred to the species E. occiden- 

 talis,' but which agree exactly, both in size and description, with 

 E. pacificus as given by Leidy and are certainly distinct from the 

 specimens described and referred by him to the former species. 



1 Proc. Am. Phil. Soc, Vol. XXII, 1884, p. 11. 



