EQUINE FOSSILS. — Leidy. 105 



Since writing the foregoing chapter, which is, however, partially amended, Dr. F. V. 

 Hayden, the zealous geologist and explorer, attached to Lieut. Warren's Expedition to 

 Nebraska, discovered on the Niobrara river, a formation supposed to be Pleiocene, which 

 contains a most wonderful quantity of equine remains, comingled with the remains of 

 many other extinct animals. In the collection of Dr. Hayden, which I have had the 

 opportunity of inspecting, I have detected the remains of apparently eight species of six 

 genera of equine animals. A particular description of these interesting remains is 

 reserved for publication in Lieut. Warren's Report of his Expedition. 



HIPPOTHERIUM.-Kaup. 

 HIPPAMON.— De Christol. 



HIPP.OTHEEIU M VENUSTUM. 

 Plate XVI. Figs. 32, 33. 



Hipparion venustum, Leidy, Proc. Acad. Nat. Sci., Philadelphia, VI, 241. 



Among the most interesting of the fossils discovered, by Prof. Holmes and Capt. 

 Bowman, in the Post-Pleiocene beds of the Ashley river, are two molar teeth of a species 

 of the equine genus Rippotherium. These were the first remains of the latter discovered 

 in America, and they indicate the smallest known species. 



Both specimens are from the upper jaw ; and they are well characterized, not only by 

 the isolation of the internal median enamel column, but also by the complex plication of 

 the interior or central enamel columns. 



The larger specimen (Plate XVI, fig. 33,) is firm in texture ; has the enamel stained jet 

 black, and the dentine and cement gray. It is broken at the bottom, and has lost its inner 

 median enamel column. In its present condition it is two inches in length ; and possesses 

 a moderate degree of internal and posterior curvature. Its antero-posterior diameter is 

 eight and a half lines, and its estimated transverse diameter at the middle is seven lines. 



The smaller specimen (Plate XVI, fig. 32,) is firm in texture, and brown in color. It is 

 half worn down ; tapers toward the root ; and is little less than an inch in length. Its 

 inner median enamel column is antero-posteriorly reniform. The breadth of the tooth is 

 seven and a half lines, and the transverse diameter five and a half lines. 



Plate XVI, Fig. 33. The triturating surface of a superior molar tooth of Hippothe- 

 rium venustum, the size of nature. Specimen discovered by Prof. Holmes. 



Fig. 32. The triturating surface of a superior molar tooth of Hippotlierium venustum, 

 magnified two diameters. Specimen discovered by Capt. Bowman. 



