GOG GEOLOGICAL SURVEY OF THE TERRITORIES. 



OKOHIPPUS, Marsh. 



American Journal Science autl Arts, 1872, (publislied August 7.) 



Superior molars, witli U\o exterual crescentoid crests, and two inter- 

 nal cones, >Ybicli are connected with the former by low oblique crests 

 which are directed, to the anterior bases of the outer tubercles. 



This genus constitutes au approximation of the LimnohyKs type to 

 Anchithcriim, and probably connects effectively the equine and tai)iroid 

 divisions. 



Orohippus procyoninus. Cope. 



Proceedings American Philosophical Society, 1872, p. 4G0, August 3. (Helothcrhim.) 

 Oroh'qyjnis pumUMs, Marsh, 1. c., August 7, 1872. 



This species is distinguished by its small size, as it did not much ex- 

 ceed the raccoon in dimensions. The size of a right superior molar is as 

 follows : 



Measurements. 



Length 0.007^ 



Width posterior "^'85 



Width auterior tJ06 



The crown presents four tubercles, of which the inner are flat on the 

 anterior, the outer flat on the external side. The anterior cross-ridge 

 has a trihedral tubercle, and a low tubercle intervenes between the two 

 posterior in front of them. Au anterior and a posterior ciugulum. 

 Enamel smooth. 



Genera Tncertw Sedis. 

 OROTHEPJUM, Marsh. 



American Journal Science and Arts, 1872, p. 217. 



Orotherium vasacciense. Cope. 

 On some Eocene Mammals, &c., p. 3. 



Lopliiotlicrhnn vasaccicnse, Cope. Proceedings American Philosophical Society, 1872, 

 July 11, (extras.) Xotharctus ramcciensis, Cope, 1. c, 1672, 474. 



This species is similar to the next in most respects, the corresponding 

 molars differing in the more elevated yoke between the tubercles of op- 

 posite sides, and the presence of a posterior median tubercle. 



Eepreseuted by a portion of the left ramus of the lower jaw, contain- 

 ing one tooth in perfect preservation. The structure of this indicates it 

 to be the second true molar, and presents certain feiitures of distinction 

 from the same tooth of the L. sylvaticnm, described by Dr. Leidy. The 

 crown presents four tubercles, which are arranged in pairs, the separa- 

 tion between the right and left lobe of each being slight, thus giving the 

 tooth the appearance of having two transverse crests as in Hydrachyus. 

 The two anterior and outer posterior tubercles are fissured by wearing, 

 but the inner posterior consists of two acute crests, which meet, pre- 

 senting an acute angle toward the adjoining tubercle. The outer pos- 

 terior tubercle sends a descending crest obliquely to the base of the inner 

 anterior tubercle, as in L. sylvaficum. A small tubercle occupies the 



