24 X 



9 



Fig. 15 represents a specimen found in association with thai of the pre- 

 vious figure of the same plate. It appears to be a third or fourth upper 

 molar, and, from the size and arrangement of enamel on the triturating sur- 

 face, might be supposed to belong to the same animal as the former speci- 

 mens. In the proportions of the tooth it resembles those of Merychippue 

 more than it does those of Hipparion. The crown is quite short, and exhibits 

 a considerable degree of curvature. It is about 2 lines long on the inner side, 

 and three times that length on the outer side. On the triturating surface the 

 antero-internal column appears as an elliptical ring, as in Hipparion, but it 

 exhibits a pointed process indicative of continuity at a later period with the 

 antero-median column, as in Protohippus and Merychippus. The tortuous 

 enamel-line on the inner part of the triturating surface presents no median 

 fold, directed toward the elliptical ring, as is the case also in the fourth molar 

 of Protohippus, as seen in Fig. 2, Plate XVII, of the Extinct Mammalian 

 Fauna of Dakota, &c. 



The antero- posterior diameter of the tooth is 7f lines, and its transverse 

 diameter 8£ lines. 



Another specimen, consisting of a mutilated, unworn molar, from its pro- 

 portions, is supposed, to belong to the same species as the former. It was 

 obtained at a depth of 30 feet from the surface in Washington County, Texas. 

 The crown internally is 5£ lines long, and has measured externally about 10 

 lines. Its breadth is 9 lines, and its transverse diameter has been but little 

 less. 



PROTOHIPPUS (?) s. MERYCHIPPUS? 



Among the Texan collection of fossils there are several which are suspected 

 to belong to one or other of the equine genera above named. 



Fig. 1G, Plate XX, represents a specimen obtained from a well, at a depth 

 of 32 feet, at Independence, Washington County, Texas. It is an upper 

 molar, apparently the second or third of the series of the usual complement 

 of six large teeth in equine animals. In its proportions it would appear to 

 belong to the genus Merychippus rather than Protohippus. The crown is 

 from 3£ to 4 lines in length on the inner side, and from 7 to 8 lines on the 

 outer side. The median enamel lakes of the triturating surface are of simple 

 character, and widely gaping, apparently indicating but comparatively little 

 wear, notwithstanding the shortness of the crown. In the appearance of the 

 triturating surface it resembles more the teeth of Protohippus perditus, as 



