1881.] ^^'^ [Cope. 



rior boundary of the crown. This crest is not divided into parts homolo- 

 gous with the intermediate tubercles. The crowns of the M. I and II are 

 surrounded by a basal cingulum, which in the M. I develops a tubercle at 

 the anterior external angle. No internal or external cingulum on P-m. 

 IV. Enamel nearly smooth. 



The ramus of the mandible is rather slender anteriorly. The P-m. IV 

 is robust, and the cusp is behind the middle of the base of the crown. The 

 heel is short and narrow, and has a raised border, connected with the base 

 of the main cusp. The cusps of the second true molar are elevated and 

 conic, the anterior external the highest, the others subequal. The base of 

 the posterior pair is a little narrower than that of the anterior pair. There 

 is no central tubercle as in Catathlmus rJiaModon, and no basal cingulum 

 on either tooth. 



Measurements. M. 



Length of three superior molars 0160 



^. . T^ ^_ c anteroposterior 0055 



Diameters superior P-m. iV ^ ^ aa«a 



^transverse 00*0 



^. . ,^ ^ f anteroposterior. 0052 



Diameters superior M. I { ^ „„„rt 



( transverse 0060 



Length of inferior molar series 0610 



" " " true molar series 0160 



^. , - . ^ ^^^ (anteroposterior 0060 



Diameters inferior P-m. IV < ^^.^ 



t transverse 0040 



„. . . . ^^ ^^ (anteroposterior 0050 



DiametersinferiorM.il i ^ r^r^.r. 



i transverse 0040 



Depth ramus at M. II 0090 



A number of minor points will distinguish this species from those in- 

 cluded among the Mcsoclonta, and especially those of Pantolestes, which it 

 most resembles. The molar teeth are narrower behind, and the fourth 

 premolar is larger. It is Miodasnus sectorius, American Naturalist, Octo- 

 ber, 1881, p. 831. 



MiocLiEisus TURGiDus, gen. et sp. nov. This genus differs from 

 Catathlmits in the structure of the inferior premolars, which are without 

 internal crest or cusp. The inner lobe of the superior premolars is less 

 developed than that genus. In the present species the characters of 

 Mioclcenus are best seen in the subconical tubercles of the premolars, 

 particularly that of the heel of the fourth inferior premolar. In the other 

 three species this heel is more of a crest and is connected with the princi- 

 pal cusp by a low ridge. The four species may be characterized as 

 follows : 



a. Cusps of last premolars conical in both jaws. 

 Size medium. Last lower molar disproportionately small ; cusps low ; 



two anterior inner distinct ; true molars, .018 M. turgidus. 



aa. Fourth superior premolar with flattened external and conic inter- 

 nal cusp : inferior unknown. 



