30 E. L. Troxell — Amynodonts in Marsh Collection, 



postero-internal corner. Remnants of the internal lake 

 indicate the presence of the two transverse crests as in 

 other specimens. 



M^ is snbquadrate in form and is much shorter, antero- 

 posteriorly, than it is wide (27 by 38 mm.). IV'P forms 

 an irregular quadrilateral with the longest sides anterior 

 (42 mm.) and exterior (43 mm.). The outer side of its 

 ectoloph is apparently entirely smooth, the cingulum and 

 the groove marking off a parastyle both being lost by 

 wear. On ]\P and M^ there are hea\^^ posterior cingula 

 inclosing depressions (postsinus) and the broad incon- 

 spicuous antecrochets are set off by grooves extending 

 down the protocones. 



]\P has three sides at right angles, while the side of the 

 ectoloph runs on a diagonal. The diameters are : antero- 

 posterior, 36 mm., and transverse, 39 mm. The outer 

 side of the tooth is divided into two areas, or grooves, by 



Y P M. 



Fig. 4. — Amynodon erectus, sp. nov. Holotjpe. Side view of skull. 

 X 1/6. 



a strong ridge opposite the paracone. There is a distinct 

 parastyle. The continuation of the ectoloph beyond its 

 union with the metaloph offers one of the distinguishing 

 features of the Amynodontidse. 



The postsinus is much deeper than that in the holotype 

 of A. advenus Marsh (Cat. No. 11763, Y. P. M., fig. 7). 

 In the latter the cingular ridge does not inclose a depres- 

 sion, anterior or posterior, nor does the cingulum extend 

 across the end of the median valley. On the other hand, 

 M^ of ^. erectus, sp. nov., in fact, each of the molars, has 

 a strong cingulum anteriorly and a decided internal basal 

 ridge extending across the medisinus which rises into 

 a small cusp, as in certain diceratheres. 



Loiver jaivs. — One ramus of the mandible is almost 

 complete, including its dentition. The body is narrow 



