E, L. Troxell — Amynodonts in Marsh Collection. 2T 



lake or remnant of the diagonal medisinus. The tooth 

 forms a parallelogram elongated transversely ; its diame- 

 ters are 37 and 53 mm. 



M^ has its back, inner, and front sides at right angles, 

 but the outer side is an oblique line. The longest dinien- 

 sions are, on the outside, 51 mm., and the front side, 

 60 mm. The medisinus forms a deep sharp groove, 

 directed inward and then forward, uninterrupted by a 

 cingular ridge or basal cusp on its outer end; the post- 

 sinus is rather deep, with a sharp fold inward. M^ and M^ 

 show no groove, at the present state of wear, separating 

 the parastyle ; thus the outer walls are smooth and flat. 

 M'% however, shows this groove distinctly. 



In form, M^ is very much like M^, but it has a narrower 

 posterior side ; it has the postsinus formed by the exten- 

 sion of the ectoloph, so typical of the family and so differ- 

 ent from all other Oligocene rhinoceroses. On this tooth 

 the internal basal cingulum swings into the medisinus, 

 partly filling the groove. The posterior cingulum is much 

 lighter than that of Amynodon. In contrast to the pre- 

 molars, there are no folds of enamel on the walls of the 

 transverse crests, but the enamel of the molars is gener- 

 ally thick and heavy. 



A portion of the right ramus No. 12043 of a fossil 

 rhinoceros may belong to a Metamynodon; the three 

 teeth are probably P4, M1.2 ; they increase rapidly in size 

 so that the M2 is larger than that of any Oligocene rhino- 

 ceros known to the writer. Its great length and high 

 crown are very striking features. The small premolars 

 and the probable lack of Pj, perhaps of P2, lend weight to 

 the identification as Metamynodon. 



Summary of Metamynodon rex, sp. nov. — The main 

 differences between the two species of Metamynodon may 

 be summed up as follows : premolars of M. rex, sp. nov., 

 only submolarif orm ; the type has no postorbital promi- 

 nence rising from the malar such as appears in M. plani- 

 frons; the zygomatic suture either forms a sharp angle 

 or leads from within the orbit ; P^ has three fangs instead 

 of two. • The much smaller molar length, relative to the 

 premolar length, results partly from the greater age and 

 wear, especially on M^ 



