186 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [VolYI. 



The details of the inferior teeth preserved do not differ much from 

 those of the U. bisulcatus, excepting that the heel of the last true molar 

 is much more produced. 



The U. acutidens is considerably larger than either of the species of 

 the genus heretofore described. 



Measurements, 

 No. 1. 



M. 



. vertical 0065 



Diameters of last inferior molar ^ anteroposterior 0130 



( transverse 0064 



c anteroposterior 0095 



Diameter^of atruemolarJ^^^^g^gj.gg OO-,^ 



f anteroposterior 0097 



Diameters of last superior molar j^^^^^g^^j,^^ _ _ ^130 



No. 2. 



Length of five superior molars preserved. » 0410 



Length of premolar series - 0325 



Length of bases of Pm. I and II 0125 



e anteroposterior 0097 



Diameters of Pm. Ill J ^^.^^g^g^g^ 0093 



f anteroposterior 0086 



Diameters of first true molar j^^^^g^gj,^^ 0^33 



Anteroposterior width of base of crown of canine 0080 



Transverse width of base of crown of canine 005U 



12. ESTHONYX SPATULARIUS Cope. 



American Naturalist, 1880 (Nov. 25), p. 908. 



Represented by five molar and premolar and two incisor or canine 

 teeth, apparently belonging to one individual. These are about the size 

 of those of E. bisulcatus, but present several differences of detail. Thus, 

 the basin of the heel of the last inferior molar is not obliquely cut off by 

 a crest which extends forwards from the heel, bat is surrounded by an 

 elevated border, which rises into a cusp on the external side. The 

 incisor-canine teeth are more robust than those of U. bisulcatus, one of 

 them especially having a spoon-shaped crown, with the concave side 

 divided by a longitudinal rib, on which the enamel is very thin. The 

 enamel descends much further down on the exterual than the internal 

 side of these teeth. The rodent-like tooth does not accompany the speci- 

 men. Length of base of last inferior molar, .009 • width anteriorly, .005; 

 length of crown of canine-incisor 'No. 1, .009; width at base, .005; length 

 of crown of second canine-incisor at base, .012 ; width, .006. 



MESODONTA. 



13. Hyopsodus paulus Leidy. 

 Numerous specimens. 



14. Hyopsodus vicarius Cope. 

 Less abundant. 



