PETERSON: THE AMERICAN DICERATHERES. 



409 



In comparing (D) No. 2467 in the above table with the description by Dr. 

 Loomis of his pi'oposed species Diceratherium schiffi it will at once be observed 

 that while the general contour of the skull agrees fairly well, the dentition totally 

 disagrees in the presence of the minute canines^ and the difference of the config- 



FiG. 4. 



Upper dentition of Diceratherium cooki, C. M., No. 2463, showing the reduced condition of 

 ?•* of right side and accessory tubercles on IVP. X i- 



uration of the grinding surfaces of the teeth. We are not permitted, therefore, 

 according to the usually accepted view to refer this specimen to the above pro- 

 posed species. The same comparison with (G) No. 2408 shows that while the 

 dentition agrees, the contour of the skull is less in accordance with the above- 

 mentioned description, and corresponds better with the original type of D. cooki, 

 sexual characters excepted. With another female skull (E) No. 1855, one of the 

 original .specimens used as a paratype in my earliest paper, D. schiffi seems to agree 

 best, except that the temporal ridges come closer together before reaching the 

 inion. It is thus seen that in comparing female skulls it is frequently found that 

 dentition and contour of skull do not both agree; on the contrary the material 

 affords numerous different combinations. There are of course female skulls which 

 occasionally answer to the description by Loomis somewhat more closely than in 

 the cases stated above. However, it is quite obvious that we would create a 

 difficult task for the systematist and student, not to say a non-scientific record 

 of the subject, were we to establish additional species founded upon our abundant 

 material. The different patterns of the premolar and molar teeth which were 

 formerly regarded as satisfactory for the establishment of species are obviously 

 not to be relied upon, at least not in connection with the study of the material 

 from the Agate Spring Fossil Quarries. The differences to which allusion is here 



* The canines are probably deciduous teeth, which sometimes abnormally persist and their presence 

 may be regarded as only an individual peculiarity. Professor Owen speaks of a canine in the foetal 

 skull of Rhinoceros indicus ("Odontography," p. 592). 



