MARSUPIALIA. 797 



The mental foramina are, as in P. fugax, below the first and fourtk 

 molars. The last inferior molar is as long or nearly as long as the penulti- 

 mate, but has a rather narrower heel, always with three small cusps. The 

 external anterior cusp is always much larger than the two internal, whicli 

 are well apart, and not much elevated. In some specimens, as in P. fugax, 

 there is a distinct third cusp on the posterior triangle, on its posterior inner 

 border, but it is sometimes obsolete, and sometimes wanting. Hence the 

 species, P. stevensonii, founded on this peculiarity, must be suppressed. 



Measurements. -^ 



Length of deutal series, omitting canine and Pm. 1 (No. 1) 0072 



Length of first true molar 0013 



Elevation of first true molar 0010 



Length of third true molar 0013 



Depth of ramus at third true molar 0019 



Length of last two molars 0029 



Length of third true molar 0015 



Elevation of third true molar 0012 



Depth of ramus at third true molar 0020 



I have portions of seven mandibular rami of this species, which were 

 found at the same locality as the preceding species. It is dedicated to my 

 friend Professor T. Sterry Hunt. 



Peratherium scalare Cope. 



Herpeiotherium scalare Cope. Synopsis New Vertebrata from Colorado, 1874, p. 7. Ann. Report U. S. G. 



Survey Terrs., 1873 (1874), p. 467. 

 Plate LXII ; figs. 17-18. 



This species is represented by portions of the mandibular rami of twa 

 individuals of the size of those of the P. fugax. These only support some 

 of the posterior molar teeth. 



The species is readily distinguished by the increased disparity in the 

 elevations of the anterior and posterior portions of the molar teeth, resem- 

 bling in this respect the Peratherium alternans. It is a considerably larger 

 species than the latter, and exhibits a distinct anterior cusp, of moderate 

 elevation, which is separated from the median external by a deep notch. 

 It is entirely on the inner side, and sends a cingulum to the external base 

 of the outer median. Fourth molar largest; heel narrowed, with three 

 tubercles. 



The masseteric fossa is well defined, and is bounded antei'iorly by the 

 strong external ridge of the base of the coronoid process. This ridge i& 



