E. L. Troxell — Amynodonts in Marsh Collection. 31 



and somewhat rounded, as in Equus; the horizontal por- 

 tion is deep and strong, the ascending ramus is wide 

 \qI. A. antiquus) and has a thick anterior border with a 

 deep depression exteriorly. 



rf453 TYPE 

 Y. P. M. 



Fig. 5. — Amynodon erectus, sp. nov. Holotype. Side view of lower 

 jaws showing erect canines and reduced premolars. X l/^- 



The lower teeth of this new species are of especial 

 interest, furnishing new features of Amynodon. The 

 first lower incisor is largest, and is worn off squarely on 

 the end like those of the horse, while the third incisor is 

 smallest and shows the spatulate, subconical crown with 

 a strong cingular ridge on the posterior side. M. plani- 

 frons is said by Scott and Osborn (1887, p. 167) to reverse 

 this order in the lower jaw, but to follow it in the upper 

 incisors, a rather unusual thing. 



The canine leaves the alveolar border directed for- 

 ward but curves upward to an erect position. It is worn 

 on the front side by the third upper incisor ; more signifi- 

 cant still, however, is the wear on the posterior side by 

 the superior canine, which must therefore have been much 

 more nearly erect than that of A. intermedins. It resem- 

 bles in this respect A. antiquus, which is shown to have 

 had an erect lower canine (Scott and Osborn 1883, pi. 5). 

 The transverse diameter is 16 mm., the antero-posterior 

 18.5 mm. There is a diastema of about 35 mm. between 

 Ci and P2, Pi being obsolete. 



The length of- the series of three existing lower premo- 

 lars is 45.7 mm., of the three molars 97.4 mm. P2, the 

 first of the series, is small, conical, vestigial ; it has two 

 depressions on the inner side, and a basal ridge. P3 is 

 intermediate in size, but has a form similar to P4, which in 

 turn is submolarif orm. 



