COPE ON NEW EXTINCT VERTEBRATA. 385 



other originates near the corresponding position at the opposite end of 

 the surface, and then curves on itself, forming more than a semicircle. 

 Between these and the more convex side of the tooth are three elongate- 

 oval enamel areas, the two longest of which overlap each other. On the 

 opposite side of the principal areas there is but one lesser area, which 

 is adjacent to the median extremity of the less curved of the principal 

 areas, and parallel with its inner half. The shaft is a good deal more 

 compressed at the base, and the long diameter is somewhat greater than 

 above. One side of the shaft is convex in both directions; the opposite 

 side is concave in the long direction, and slightly convex transversely. 

 The enamel is obsoletely rugose. 



Measurements. 



M. 



Length of crown as worn 0.0130 



Diameter of griuding-face 



( long 0.0075 



I short 0.0050 



The size of this species was at least that of the American porcupine. 

 The remains on which it is founded were found by E. S. Hill in the 

 Loup Fork beds of Kansas. 



Mylodon sodalis, sj». nov. 



The occurrence of this genus of sloths in Oregon was pointed out some 

 years ago by Professor Leidy, as indicated by a specimen preserved in 

 the museum of the Smithsonian Institution, but the means of determining 

 its specific relations to the other species of the genus were not at that 

 time extant. A number of phalanges, including those of the ungues, 

 contained in my collection, demonstrate that the species of Oregon was 

 quite different from those of the eastern portion of North America. 



The ungual phalange selected for description has its basal sheath 

 developed on one side only ; its place is taken on the opposite side by a 

 prominent rim, which is tuberculate and notched. The rim is low on the 

 superior part of the proximal extremity, and is separated from the artic- 

 ular cotylus by a concave subvertical surface, wider than long. The 

 basal tendinous insertion is subdiscoid and flat, with a lateral projecting 

 rim, which is pierced at the base by the arterial foramina. The general 

 form of the phalange is more compressed than in Mylodon harlani. Its 

 superior middle line is broadly rounded, and continues nearly uniform 

 to the apex. One side is subregularly convex; the other is divided into 

 three planes. The middle one of these is flat, and terminates in a short 

 lateral ridge which extends to the apex. The superior plane becomes 

 .somewhat concave near the apex, and the inferior gently convex. 



The proximal phalanges have the form usual in the genus. They are 

 rather short, and with the trochlear tongues and grooves strongly 

 marked. The proximal extremities are especially expanded in the ver- 

 tical direction. 



