Art. XVI.— On the Extinct Species of Rhinoceridse of 

 TVortli America and their Allies.* 



By E. ». Cope. 



Twelve species of mammals which may be called rhinoceroses, have 

 been defined from materials obtained from the Tertiary formations of 

 ]S"orth America; and five additional species have been distiugnished, 

 which may be regarded aB more or less nearly allied to that family. A 

 few additional names have been proposed for sui^posed species whose 

 characters are not yet established. In the corresponding formations of 

 Europe and Asia, the fossil remains indicate a still larger number of 

 species. The forms here included first appear in both continents in the 

 Lowest Miocene or Oligocene epochs ; that is, in ISTorth America in the 

 White River formation. 



The proper definition of the family Ehinoceridce is not yet perhaps 

 attainable, owing to our ignorance of the structure of some of the earlier 

 forms. The description given by Huxley t is evidently not designed to 

 be a family diagnosis, as various generic and other characters are intro- 

 duced. Perhaps the dental formula at the head of his article may be 

 regarded as such, from the context. It is I. ^^ or ^-^^ ; C. ^^ ; 

 Pm. —^ ', M. 1^ . Of this it may be remarked that the superior in- 

 cisors are sometimes 2 — 2; the canines are frequently ^j and the 

 premolars are often |5| . A little later,| Professor Gill offered a special 



diagnosis, as follows : 



" aa. ISTeck abbreviated. Incisor teeth (attypically reduced in number 

 or entirely supi^ressed. [Bliinocerotoidea Bhinocerotiformia.) 



" Skull with the basioccipital comparatively well developed behind 

 and narrowed forwards (with tympanic and peri otic bones anchylosed 

 and wedged in between the squamosal, exoccipital etc., Huxley), with 

 the nasal bones produced forwards and more or less arched and meeting 

 an upward development of the supramaxillary bones. Upper molars 

 with a deep valley extending obliquely inwards from the median portion 

 of the inner wall, and (P. M. 4, M. 1 — 2) a shallow one extending from 



* Read before the National Academy of Sciences, April, 1879. 



t The Anatomy of Vertebrated Animals, p. 307, 1872. 



t Arrangement of the Families of Mammafls: Smithsonian Misc. Pub. Nov. I873, 



P-^^- 227 



