COPE.] PALEONTOLOGY LOUP FORK EPOCH. 521 



from the bottom of the valley between the inner extremities of the 

 cross-crests in the last and penultimate molars of A. megalodiis, la 

 wanting in the A. crassus; partly on this account I refer my second large 

 Pliocene rhinoceros to the latter, represented by a perfect cranium, 

 with dentition of both, jaws nearly complete, with large portions of skull 

 and dentition, with other bones, of other specimens. 



The nasal bones are not co-ossified, and but little convex. They are 

 smooth and long and slender, indicg,ting that this rhinoceros was with- 

 out a horn. The inion is anterior to the line of the occipital condyles, 

 and is considerably elevated and bilobed. The temporal fossse ap- 

 proach each other, being separated by a narrow rib only. The ramus 

 mandibuli is rather slender, and projects well in front of the line of the 

 nasals. The dentition is I., ^; C, %-, F.m.,^-^^; M., |. The usual anterior 

 premolars are wanting in the lower jaw, and in the upper jaw in one 

 specimen and on the right side of the other; hence I suspect f to be 

 the normal dentition of the species. As they are f in Bhinocerus and 

 Aceratherimn, the present animal may be placed in another genus under 

 the name of Aphelops. The middle incisors were caducous. The outer 

 are very large and cyliudric at base; the attrition of their inner faces 

 would indicate an opposing pair, but these I did not find, and the pre- 

 maxillary sutures of the maxillary are exceedingly slender. The first 

 lower premolars are not very narrow. The transverse crests of the 

 superior molars widen inwardly, but do not come into contact with each 

 other. On the posterior margin of the posterior is a deep notch, which 

 almost divides it across. There are no other lobes. The last molar is 

 narrowed. These teeth are notable for their very large size as compared 

 with that of the skull generally. In one specimen, P. m. 2 (the anterior) 

 is 0.8 the second molar in transverse diameter; but in an older specimen 

 it is less than half the same. 



Measurements. 



M. 



Length of molar series 0.255 



Leugth of second molar, crown 050 



Width of second molar, crown 050 



Width of second premolar, crown 083 



Leugth of second premolar 032 



Length of hrst (second) lower premolar 028 



Width of first (second) lower premolar 016 



Total length of cranium 560 



From inion to end-nasals 456 



From foramen magnum to inion 138 



Width at orbits 173 



Depth of mandible at first molar 070 



About the size of the Indian rhinoceros, but with much larger teeth. 



ACERATHEEIUM CRASSUM, Leidy; Aphelops crassus, Cope, Bull. U. S. 



Geol. Surv., No. 1, 1874, p. 12 ; Ehinoceros crassus, Leidy, Auc. Fauna 



Dak. and iSIeb., &c., p. 228. 



Leidy states that the formula of dentition of this species is identical 

 with that of the Indian rhinoceros, and elsewhere that it is probably 

 a true rhinoceros, as distinguished from J^cerat/iermw. He does not ap- 

 pear to have possessed material to verify these statements. 



An im])erfect mandibular ramus, containing the last molar and alveoli 

 of the four teeth which precede it, differs from the corresponding one of 

 A. megalodiis in the greater thickness in proportion to the depth. It is 

 absolutely both shallower and thicker than a corresponding ramus of 

 the allied species, while the teeth are larger, the last three occiip;yiDg 



