Hatchkr : I,rni,K. Known Fossil \'i:Ri-Kr,RATr.s. 135 



structure with the superior molars of OroJiippus, and I have provision- 

 ally referred it to that genus. I refrain from proposing for it a new 

 generic name, while at the same time recognizing the improbabiHty 

 that the genus Orohippus should have existed continuously from the 

 Bridger Eocene to the White River Oligocene. The unexpected 

 occurrence of a tooth of this pattern, indicative of an animal closely 

 allied to the middle Eocene equines, would appear to justify a notice 

 of its discovery, with a brief description of its principal characters, 

 though its exact generic and specific distinction will be deferred until 

 the discovery of additional material shall make known its true affinities. 

 This tooth, which appears to be the left first superior molar, was 

 found by Mr. W. H. Utterback at the base of the Titanotherium Beds, 

 in an exposure about one mile south of Henry's Dam, on Squaw 

 Creek, in Sioux County, Nebraska. A crown view of it is shown 

 on Plate I, Fig. 7. It agrees almost exactly in size and structure 

 with the first molar of Orohippus as figured by Wortman on page 108, 

 Vol. VIII of the Bulletins of the American Museum of Natural His- 

 tory. The crown is in outline almost a perfect square, and supports 

 four subequal cones, each occupying one of the four angles of the 

 tooth. In addition to these four principal cones there are two small 

 intermediate cones, or conules. A basal cingulum surrounds the 

 tooth except on the inner side. This tooth has an anteroposterior 

 diameter of .009 metres and a maximum transverse diameter of .0095 

 metres. 



Trigonias osborni Lucas. ^° 



Dentition, I.f, C.^, P.|, M.| = 42. None of the upper pre- 

 molars are strictly molariforin. Skull much elongated and very large in 

 comparison with the size of the skeleton. Manus tetradactyl. 



This new genus of the early Oligocene Rhinoceridoe is represented 

 in our collections by two skulls and one nearly complete skeleton, 

 beside numerous other bones, all from the lower Titanotherium Beds 

 of the White River Oligocene. Only a very small portion of this 

 material has as yet been unpacked and freed from the matrix. It is 

 the intention of the present communication to record only a few of 

 the more important characters, reserving a description of the com- 

 plete osteology for a future paper, after all of our material has been 

 prepared for study. 



'"See Proc. Nat. Museum, Vol. XXIII, No. 1207, pp. 221-22J. 



