COK^DYLAETHEA. 407 



M. 



Length of four premolars 017 



Length of base of crown of Pm. ii 0045 



Diameters of inferior M.ii^'"'*''^"?''***'"''' 0046 



c transverse 004 



No. 2. 



Length of superior true molars 013 



Diameters M. „ ^ anteroposterior 0045 



( transverse 007 



Diameters M. iu ^anteroposterior 004 



( transverse 006 



Diameters Pm. 1^5 anteroposterior 005 



( transverse 007 



This species was found by Mr. D. Baldwin in the lowest beds of the 



Puerco formation in Northwestern New Mexico. I dedicate it to Dr. 



Waldemar Kowalevsky of Moscow, one of the most able of the European 



paleontologists. 



Hemithl^eus opisthacus Cope. 



Proced. Amer. Philos. See. 1882, p. 467. Mioclaeiim opisthacus Cope, American Naturalist 1882, p. 833 



(September 20). 



Plate XXV f; figs. 8-9. 



This species is known from fragments of four mandibles, and a broken 

 last superior molar tooth, found together by Mr. Baldwin. The mandibles 

 belong to one species, and there is nothing to cast doubt on the reference 

 of the superior tooth to the same. This tooth refers the species to the 

 genus HemithlcBus. 



This species resembles its congener in the abrupt diminution in size of 

 the premolars anterior to the third. The contrast between the second and 

 third is greater than in the H. kowalevsJcianus. The anteroposterior extent of 

 the former is little more than half that of the latter. The third and fourth 

 premolars are large and oval in horizontal section, and quite similar in size 

 and form. The heel of each is small, and has a median elevation, and that 

 of the fourth is a little the larger. The fourth premolar is not larger than 

 the first true molar. The true molars become narrower posteriorly, and the 

 first is as large as or larger than the second. The anterior two cusps of thd 

 molars are more elevated than the posterior; they soon unite on attrition. 

 There is no interior median cusp, but a narrow ledge in front of the ante- 

 rior cusps, on the second and third molars; the first is worn on all the 



