80 GEOLOGICAL SURVEY OF TEXAS. 



EQUUS SEMIPLICATUS, CopC. 



Plate XXIII, Figures 2, 3. 



Sp. nov. Equus fraternus, Leidy, Cope, Am. Naturalist, 1889, 

 p. 161; not of Leidy. 



Represented by two superior molar teeth from the Tule Canyon, found 

 by Mr. Cummins, and by two superior molars in my private collection 

 from San Diego, in southwest Texas, from Mr. "Wm. Taylor. 



These teeth indicate a species of about the dimensions of the E. tau, 

 but characterized by a greater complexity of the enamel foldings. These 

 complications are con lined to the adjacent or median borders of the lakes, 

 the remote borders being simple or marked by a single emargination. 

 There is no distinctly defined loop of the posterior border of the anterior 

 lake, but its place is taken by three smaller loops (in one south Texas 

 tooth by two), and external to these are one or two other folds. There 

 are two or three emarginations of the opposed border of the posterior 

 lake. In all the Texas specimens the anteroposterior diameter of the 

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

 character places the Equus semiplicatus in the same group as the E. excel- 

 sus and E. tau. From the former its inferior size distinguishes it, as 

 well as the closer plications of its enamel borders. Some specimens of 

 the larger species, however, approach it in this respect. 



Measurements. 



Mm. 



Diameters superior molar (Tule Canyon) . . . . -j anteroposterior 25 



( transverse 25 



Diameters superior molar sp. from San Diego \ f" ^lopos enor 



(transverse 27 



The crowns of the Tule specimens are rather short and are not curved; 

 the least worn San Diego specimen has a long crown, which is slightly 

 curved anterposteriorly, but not transversely. 



The characters of the grinding face resemble those of the E. conversi- 

 dens, Owen, so far as the latter can be understood from Owen's figures. 

 But in that species, according to Owen, the crowns are transversely 

 curved, while in E. semiplicatus they are straight. 



EQUUS EXCELSUS, Lcidy. 



Plate XX, Figures 4, 5; XXII, Figures 4, 5. 



This is the characteristic true horse of the Equus bed of the western 

 parts of North America and of Mexico. It is represented in the Staked 

 Plain collection from Mr. Cummins by the following specimens: First, 

 two superior molars (one entire) and an inferior molar, found together 

 (No. 48); second, a nearly entire superior molar (No. 51); third, two in- 



