ipoi,] Gidley, The North American Species of Equus. I 29 



(20) Equus semiplicatus Cope. 



Type Locality. — Rock Creek, Brisco Co., Texas. 

 Horizon. — Sheridan Beds. 

 Type. — Superior molar m= (?). 



Author s description. — " These teeth indicate a species of about the dimen- 

 sions of the E. tail, but characterized by a greater complexity of the enamel 

 foldings. ... In all the Texas specimens the antero-posterior diameter of 

 the protocone is more than half that of the grinding face of the crown. This places 

 the Equus semiplicatus in the same group as the E. excelsus and E. tau. From 

 the former its inferior size distinguishes it, as well as the closer plications of its 

 enamel borders. . . . The characters of the grinding face resemble those 

 of the E. conversidens Owen, as far as the latter can be understood from 

 Owen's figures. But in this species, according to Owen, the crowns are trans- 

 versely curved, while in E. seniipUcatus they are straight." 

 Meastirements given. 



Diameters superior ( Antero-posterior 25 mm. 



molar (Tule Canon) ( Transverse 25 " 



Diameters superior molar ( Antero-posterior 25 



(sp. from San Diego) ] Transverse 27 



A comparison of the measurements will show that the teeth of 

 this species are very much larger than 

 those of E. tail, and are even larger than 

 those of E. converside7is as given by Owen. 

 The species seems to be about intermediate 

 in size between E. compiicatiis and E. con- 

 versidens, and is about the size of E. /ra- 

 ter mis. Its tendency to a very simple tooth 

 pattern, however, seems to distinguish it 

 from the latter species, 



A skull from southwestern Texas, now in 

 the American Museum collection (No, 

 8600), which Cope had previously described, 



and referred to E. excelsus,'^ and which was again mentioned and 

 figured in his Rept. Geological Survey of Texas, p. Si, PI. 

 xxii, Fig. 3, differs not at all from Cope's description, measure- 

 ments, and figures of E. semiplicatus, but does differ in both size 

 and general character from Leidy's type of E. excelsus. Also, 

 coming from practically the same locality as the type specimen 

 of E. semiplicatus, and from the exact locality from which two of 

 the paratypes were collected, it seems to belong more properly to 

 the latter species than to E. excelsus. 





Fig. 20. Equus semi/'ti- 

 rrt/7/j- Cope(type_). Superior 

 molar. (After Cope.) 



\_May, 1901.] 



^ Am. Naturalist, i8gi, p. gi2 



