1883.] ^61 rCope. 



cuius; and tlielast true molar of the latter is half as long again as the pen- 

 ultimate, while in M. pungens it exceeds it but little. 



The best preserved true molar is the second. Its most elevated cusps 

 are the anterior and posterior inner, of which the anterior is subconic and 

 more elevated. The anterior external cusp is crescentic in section, and 

 sends crests to the supplementary, anterior, inner and the posterior anter- 

 ior inner, both of which descend inwards. The posterior crest reaches the 

 posterior base of the anterior inner cusp. 



The posterior external cusp is an elevated angle, sending crests forward 

 and backwards. Tlie former reaches the base of the anterior external 

 cusp (not reaching the inner), while the latter passes round the posterior 

 edge of the crown. As in 31. punrjens, it is convex posteriorly, and rises 

 to the posterior internal cusp. In both species its appearance indicates that 

 it performs an important masticatory function in connection with the su- 

 perior molar. No cingula. 



Measurements. M. 



Length of base? of M. ii and iii ; (No. 2) 0125 



baseofM. iii; (No. 2) 0070 



Diameters crown M. ii; (No. 1) < anteroposterior ... .0056 



i transverse 0050 



Depth of ramus at M. ii ; (No. 1) 0100 



Peeiptychus carinidens Cope. 



Additional specimens of this species demonstrate that the last inferior 

 molar has a different form from that of the P. rJiabdodon. While of the 

 same length, it is narrower throughout, conformably with the smaller size 

 of all the other molar teeth. 



Phexacodus calceolatus, sp. nov. 



This species is founded on fragments of the skull and limbs, with teeth, 

 of a single individual. The teeth consist of two superior and four inferior 

 molars of one side, and a smaller number of those of the opposite side. 



The teeth are of the size of those of the Phenacodus ptiercensis, and like 

 that species, there is no median external cingular cusp of the superior 

 molars. In these teeth the external basal cingulum is weak, but there is 

 a strong anterior cingulum, distinct from any of the cusps. No internal 

 cingulum. External cusps conical, well separated ; intermediate cusps 

 rather large ; internal cusps rather large, close together, but deeply sepa- 

 rated. The last superior molar is reduced in size. It has well developed 

 anterior and posterior cingula, a weak external, and no internal cingula. 

 The intermediate tubercles are rather large, and there is one large in- 

 ternal tubercle. 



The heel of the last inferior molar is short, wide and rounded. The 

 posterior tubercle is but little behind, opposite the posterior internal tu- 

 bercle. The latter is separated from the anterior inner by a deep fissure, 

 while the opposite side of the crown is occupied by a large median exter- 



