1885.] NATURAL SCIENCES OF PHILADELPHIA. 33 



cylindrical handle and a wider half elliptical blade. The posterior 

 fold, as long and wider than the former, curves forward and out- 

 ward in advance of the free border of the anterior fold, coming 

 into contact with the outer face of this below, but separated from 

 it by an open crevice above. The meeting folds divide the interval 

 of the lobes of the crown into an outer trilateral pit over two 

 inches in depth, and an inner nearly rectangular recess about an 

 inch and a half in depth. A well-produced basal ridge occupies 

 the forepart of the crown; a feeble one, produced behind in a 

 tubercle, the outer part of the crown ; and a broad tubercle occu- 

 pies the base of the interval of the lobes internally. The measure- 

 ments of the specimen are as follows : — 



Greatest transverse diameter at the anterior third, 56 mm. 



Greatest fore and aft diameter externally, . 63 " 



Greatest fore and aft diameter internally, . 55 " 



Greatest depth at the antero-external border, . 63 " 



The species may be distinguished by the name of Rhinoceros 

 proterus. The subgenus, whether Acerather-ium, Aphelops,- or 

 other, is of course only to be determined b}* the supply of other 

 portions of the animal. The inferior molars and bones of a 

 rhinoceros, indicated in the former communication on fossils 

 from the same deposit, most probably also pertain to this species. 

 The extinct genus Hippotherium, a three-toed ancestor of our 

 horses, was originally described from remains found in the 

 Miocene and later Tertiary deposits of Europe. Remains of the 

 same genus were first discovered in this country in the Ashley 

 River phosphate beds of South Carolina, noticed in our Proceed- 

 ings of 1853, p. 241, under the 'name of Hipparion venustum, and 

 described in Holmes' post-Pliocene fossils, 1860, 105, pi. xvi, figs. 

 32,. 33, as Hippotherium venustum. Since then a number of 

 other species have been described by the speaker and Prof. Cope 

 from remains found in various localities of this country. The 

 tooth now under inspection is an upper molar, 

 perhaps the fourth large one of the series. It 

 indicates a small species, little more than half 

 the size of the domestic horse, or of the 

 Hippotherium gracile of Europe, and exhibits 

 sufficient difference to assume that it indicates 



\A^-J- 



.,. another species from those already described. 

 ■* s The folding of the contiguous borders of the 

 Hippotherium ingenuum. interior enamel islets of the worn triturating 

 surface is less complex than in H. venustum. and the internal islet 

 is elliptical instead of circular. The species may be named 

 Hippotherium ingenuum. The measurements of the tooth are 

 as follows : — 



Length at antero-internal corner of crown, 42 mm. 



Breadth fore and aft of triturating surface, 19 " 



Breadth transversely of triturating surface, 17 " 



