24: E. L. Troxell — Amynodonts in Marsh Collection, 



which, especially in Metamynodon, is triangular in form, 

 broad above and constricted below, and situated well 

 back on the niaxillaries, due to the abbreviated nasal 

 bones. 



We may judge further of the living conditions of the 

 Amynodontidge by the character of the teeth. The canines 

 and molars have developed with the skull and are larger 

 than those of any other rhinoceros of the period, but the 

 incisors and premolars have not kept pace and are 

 scarcely larger than in Amynodon, showing but slight 

 need for cutting teeth in these animals. The upper 

 canines of Metamynodon and of A. intermedins were 

 strongly procumbent and diverging ; they were not erect 

 in the jaw like the canines of Archceotherium. 



The molars are broad and flat and in their use must 

 have been comparable to those of an elephant, serving to 

 grind up the food secured by the canines ; this may have 

 consisted of bark, tuberous roots, nuts, or leaves, gathered 

 near the aquatic haunts, in the mastication of which the 

 molars were used, leaving no need for premolars of the 

 cutting type. 



There seems to be little wear relatively on the narrow 

 premolars ; most of it comes on the middle of the cheek 

 series, on ]\P especially. There is naturally less wear 

 on M-^ which appears last, though on this molar one sees 

 the vestigial extension of the ectoloph beyond its junction 

 with the metaloph, which serves to prolong the period of 

 usefulness of the tooth by furnishing a longer grinding 

 surface. 



In comparing these metamynodonts with the other 

 groups of rhinoceroses of the period, we see that Ccenopus 

 and Dicer atherium developed their molars more like the 

 horses, i. e., for grazing, had sharper edges on the ectoloph 

 for cutting the food, and the premolars were much more 

 advanced and more molarif orm than in any of the amyno- 

 donts. 



Description of New Species. 

 Metamynodon rex, sp. nov. 



(Figs. 1, 2.) 



Holotype, Cat. No. 10274, Y. P. M. Lower Oligoeene {Metamynodon 

 zone), Pine Eidge Agency, South Dakota. 



This fine specimen was purchased from Mr. C. H. Little 



