■^'''•2-] COPE OX EXTINCT RHINOCEEIDiE. 235 



ACEPvATHEEIUM Kaup. 

 Isis, Ton Oken, 1832; Jahrbucli fiir Miueralogie, 1832, 419; Ossemens Fossiles, 4'J-61. 



Dentition: L|; C.-J; Pm. 3^;M.|; digits 4— Sj nasal bones without 

 Lorn basis. 



This genus is cliaracteristic of the Miocene or Middle. Tertiary forma- 

 tions of Europe, and is the primitive fonn of the true rhinoceroses. Its 

 four anterior digits relate it to the lower or more generalized perisso- 

 dactylous types of the same and of older geological horizons, which are 

 equally allied to the tapirs. ThS dentition differs from that of the genus 

 Eliinocerus in the presence of two superior incisors, but agrees with it 

 in the existence of one incisor and one canine on each side below, and in 

 the forms of the premolar teeth. The species display great simplicity 

 in the character of the crests of the molars. They also possess the ta- 

 piroid feature of the non -closure of the auditory meatus below by the 

 posttympanic process ; and the postgienoid process is generally more 

 like that of the tapirs than are those of the later genera Aphelops and 

 Rhimcerus. The form of the femiu- is also quite characteristic, present- 

 ing tapiroid characters again in the shape of the great trochanter. This 

 process is not flat and obliquely truncated as in the genera above named, 

 but is horizontal proximally, and with a produced recurved apex and 

 posterior crest, which bound a large fossa. 



In this paper, four species are referred to this genus, but provisionally 

 only, on account of the absence of certain diagnostic parts of the skele- 

 ton. These species are, in the order of size, beginning with the smallest, 

 as follows: A. mite Cope; A. occidentale Leidy; A. imcificiim Leidy; 

 A. iruqidamm Cope. I only possess the feet in A. xmcificum, and these 

 are not entirely complete ; the nasal bones are wanting from all my 

 specimens. The inferior incisors or canines are present in all; but I 

 have only the superior incisor oi A. imcificum. Leidy describes that of 

 A. occidentale, and I have the premaxiUary bones with the incisive alve- 

 oli of the same. I possess the posterior cranial regions of all the species 

 except the A. tritquiamim, and these present the characters above de- 

 scribed. 



The species above mentioned are generally of smaller size than those 

 of the Loup Fork formation, which have been referred to the genus 

 ApJielops. The largest Aceratherium, A. truquianum, is not much less 

 than the smallest of the Aplielopes, A. megalodus. 



Should any of the four species here included be found to possess but 

 three toes in the anterior foot, such must be referred to Aphelops. 



