Cope.] 



124 



[Feb. 5, 



of Texas, 1890, p. 190) without exact determiaatioa of its positiou in the 

 Cenozoics. 



The Mastodon is of the M. angiistiieiis type, as indicated by the teeth, 

 but tliere are not enough fragments preserved to render it clear whether 

 they pertain to this species or to some allied one. The Equus is allied to 

 the E. occidentalis of Leidy, bat the enamel plates are more simple than 

 in that species, being the most simple koovvu in the genus. I regard it as 

 an undescribed species, and describa it below unler the name of Equu,s 

 simpUeiiens. A. second species of horse is indicated, but an exact deter- 

 mination cannot be made without additional material. The tortoise is a 

 terrestrial form. A water bird of which a tarcometatarse is contained in 

 the collection, is kindly determined for me by Dr. Shufeldt as allied to the 

 rails. 



Equus simplicidens sp. nov. 



This species is represented by one nearly entire superior molar of an 

 adult, and one of a young animal, with characteristic fragments of two 

 other superior molars, and several fragments of inferior molars. The size 

 of the teeth is about that of the E occidentalis and E caballus. The 

 internal column is of moderate anteroposterior extent, its posterior border 

 marking the anterior third of the posterior lake. Its long diameter is con- 

 siderably less than half that of the crown. A peculiarity found in two 

 of the superior molars, but not in two others, is that the median dentinal 

 connection between the external and median crescents is interrupted by 

 the continuity of the enamel plates bordering the lakes from the one 

 to the other. This arrangement is frequently 

 seen in the large pm. 3, in the species of 

 Equus, but does not occur in the other pre- 

 molars and molars. It is a reversion to the 

 condition seen in Ancliitherium. A principal 

 character of the species is seen in the extreme 

 simplicity of the enamel borders of the lakes. 

 They are without inflection, except the usual 

 loop on the posterior inner border of the ante- 

 1. Equus simpli-^ j-joi- ]ake, and this is simple and widely open 

 at the base. At the point of junction of the 

 median crescents (meta- and paraconules), the 

 usual loop of the internal enamel border is 

 seen. The external median rib is narrowed and not flattened; the anterior 

 rib is more flattened, especially at the present grinding face. 



The species with which it is necessary to compare this species is the 

 Equus occidentalis of Leidy. The enamel plates bordering the lakes in 

 that species are always more complex, although they are simpler in it than 

 in the other extinct species of North America. Even in the simplest 

 forms {e. g., that figured by Leidy in Vol. i, Report U. S. Geol. Surv. 

 Tens., 1873, PI. xxxiii, Figs. 1, 2) the lakes have anterior and posterior 



Fig. 



cidens Cope ; crown of 

 true molar of left side ; 

 natural size. 



