44 GEOLOGICAL SURVEY OF TEXAS. 



the discoveiy of four additional lower molars at Goodnight' s by Mr. 

 Cummins fixes it. It is the most characteristic species of the epoch which 

 intervened between the Loup Fork and Blanco. 



The species belongs with the E. minutus, Cope, to a section of the genus 

 characterized by the relatively great width of the metaconid-mctastylid 

 column of the inferior molars, and its close appression to the protoconid 

 and hypoconid, and hence by the relatively narrow molar crown; and also 

 by the small size. The present species is superior in dimensions to the 

 E. minutus, and differs from it materially in the small size of the hypo- 

 stylid. From this it follows that the broad flat posterior channel of the 

 internal side of the crown, which characterizes the E. minutus, is absent 

 from this species, and a narrow channel with rounded base, rising to the 

 metastylid side, takes its place. The terminal fourth of the crown has a 

 considerable cementum investment, but the remainder of the crown is 

 nearly naked, as in E. minutus. The hypostylid is sepai-ated from the 

 metastylid by a sharp groove in the E. simplicidens; and this rib and the 

 metaconid are more prominent in that species. In this species and in the 

 E. minutus, as in some of the teeth of the horse and the quagga, the deep 

 enamel inflection of the external wall enters the metaconid-metastylid 

 isthmus. In the single molar of E. eurystylus this is not the case. The 

 anterior and posterior faces of the crown are flat in both the E. eurystylus 

 and the E. minutus, and the crowns of the teeth observed are gently 

 curved anteroposteriorly. 



Anteroposterior diameter of crown at middle, 20 mm.; ditto of meta- 

 conid-metastylid, 13 mm.; transverse width of crown restored, 11 mm. 

 Corresponding measurements of ^. simplicidens, 30 mm., 18 mm., and 18 

 mm. respectively. 



Other specimens examined since the above description was written 

 throw much additional light on its characters. These are four inferior 

 molars, all from Goodnight' s, and all apparently from as many individ- 

 uals. From these it seems that the external faces of the protoconid and 

 hypoconid are flat and not convex as is usual in this genus. Also that 

 the hypoconid throws outwards an acuminate or acute loop just before 

 joining the protoconid, which loop is the summit of an acute ridge of the 

 middle of the external face of the crown. Next, the hypostylid is much 

 more extended anteroposteriorly than is represented in Plate XX, fig. 6, 

 where it is indeed rather smaller than in the tooth from which it was 

 drawn, owing to the latter being fractured at that point (see fig. 6a). 

 It is not flat on the inner face as in E. minutus, but is convex, and has a 

 posterior recurved crest, which forms a posterior marginal ridge of the 

 crown. This ridge is not equidistant from the metastylid in the different 

 specimens. It is nearest the latter in the tooth first described (No. 1) 

 and figured, as above cited. In another specimen (No. 5) it is not 



