. Bulletin of the Department of Geology. Geology. 4 University of California Publications in Geology [Vol. 9 Miocene. E. eurystylus is distinguished by extreme narrowness of the lower molar crowns, by the great anteroposterior diameter of the metaconid-metastylid column and its close ap- pression to the protoconid and hypoconid, and by the presence of an anteroexternal ridge on the protoconid and one on the hypoconid. Those characters of E. eurystylus appear in no. 19414 from Thousand Creek. The lower molar (M2) from Thousand Creek is very long and narrow and was heavily cemented. The anteroex
. Bulletin of the Department of Geology. Geology. 4 University of California Publications in Geology [Vol. 9 Miocene. E. eurystylus is distinguished by extreme narrowness of the lower molar crowns, by the great anteroposterior diameter of the metaconid-metastylid column and its close ap- pression to the protoconid and hypoconid, and by the presence of an anteroexternal ridge on the protoconid and one on the hypoconid. Those characters of E. eurystylus appear in no. 19414 from Thousand Creek. The lower molar (M2) from Thousand Creek is very long and narrow and was heavily cemented. The anteroexternal ridges on the protoconid and hypoconid are strongly developed, as in E. eurystylus. As in Cope's species, the external ridge on the hypo- conid forms a prominent ridge on the middle of the external face of the crown. Gidley3 held that Cope's Equus eurystylus represented the genus Hipparion. While it is true that the anteroexternal ridge of the proto- conid and most of the other characters of E. eurystylus may appear in milk teeth of Equus, Cidley's reference of this form to a group in or near Hipparion is well supported. Specimen no. 19414 from Thousand Creek. 3 Fig. 3. N eohipparion leptode, n. sp. M.,, no. 19414, type specimen, represents a species in many respects near Neo- natural size. loner and Upparion eury style? (Cope). The Thousand occlusal views, Thousand 11 u -j \ i / Creek, Pliocene, Thou- Creek form is larger and the details of structure sand Creek, Nevada. ,„ . ,, ,. „, . , ., are sufficiently different to separate the two, at least, tentatively. It also resembles other American forms of the Hipparion group, as Neohipparion oecidentale, in many characters, but seems not clearly referable to these species. The writer has, there- fore, referred the Thousand Creek form tentatively to a distinct species. Measurements N. leptode, no. 19414 N. eurystyle M,, greatest anteroposterior diameter 29+ mm. 24 M2, transverse diameter 11 10 M,, greatest length of crow
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