SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. 77 



Proterotherium nitens Ameghino. 



(Plate IX, Fig. 4.) 



Proterotherium nitens Anxtg\\.\ ^fenum. Synopt, etc., 1894, p. 37. 



The propriety of separating this species from P. cavtini is very doubtful. 

 It agrees well with the latter in stature and in tooth-pattern, especially in 

 the diagnostic character of the small size of the tetartocone in p- and - but 

 differs in the absence of the hypocone in m-, and the small prominence 

 of the external vertical crests, particularly of the mesostyle. This median 

 ridge is quite obsolete in p- and - and low and inconspicuous in the 

 molars. The cast of the type-specimen, however, gives the impression 

 that the jaw has been rolled and abraded and some of the teeth are more 

 or less broken. Besides, such a character may well be individual rather 



than specific. 



Measurements. 



Upper dentition, length . . . .068 P^, width 013 



" premolar-molar series, length .037 Upper molar series, length . . .031 



Pl, length (2. e., ant. -post, diam.) . .0085 Mi, length 010 



" width (z. ^., greatest trans, diam.) .0075 " width 017 



P-^, length 0085 M^, length 0115 



" width 010 " width OI7S 



P^, length 010 M^, length 0095 



" width 012 " width 017 



P^, length . . . . . .011 



Localities. — Not given. 



Proterotherium karaikense Ameghino. 



(Plate IX, Fig. 3.) 



Proterotherittm karaikense Amegh.; Anales del Mus. Nac. de Buenos 

 Aires, Ser. 3, T. Ill, p. 299. 

 This is a well-defined species, in which the molar pattern more nearly 

 approximates the perissodactyl type than in any other known Santa Cruz 

 representative of the family. The type specimen is a fragment of the 

 left maxillary, containing the five posterior teeth in intact and almost 

 unworn condition. In p- the anterior conule is hardly indicated, the 

 tetartocone is extremely small, and on the outer face the mesostyle is 

 quite obsolete. P- is more completely molariform than in P. cavum, 

 having a somewhat better developed tetartocone and more quadrate shape. 



