SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. * 37 



DiADiAPHORUs ROBUSTUS Ameghino. 



I (Plate III, Figs. 1-3.) 



D. robustus Amegh.; Enum. Synopt. des Mamm. Foss. de Patagonie, 



1894, p. 47. 

 D. majusculus Lydekker, in part; Anales del Museo de La Plata, T. II, 



1893. P- 59- 

 D. ccelops Amegh. ; Anales del Museo Nacional de Buenos Aires, Ser. 3, 



T. Ill, p. 477. 



This species, which is not represented in the Princeton or the New York 

 collections, is known to me only from a cast of the type-specimen and from 

 Lydekker's figure ('93, PI. XXIV, fig. 2). These indicate an animal of 

 about the same size as D. majtisctUus, but rather more robust. The upper 

 tusk is considerably stouter and is followed by a shorter diastema ; in m- 

 and - the posterior conule is placed so near to the postero-internal cusp 

 as almost to block the connection between the posterior fossa and the 

 median valley, so that, in a comparatively early stage of wear, the fossa is 

 isolated as an enamel lake. In the lower jaw the small median incisors 

 are separated from each other but are in contact with the large, tusk-like 

 laterals, which are very strongly divergent. The canine follows the lateral 

 incisor without a diastema, and the first premolar is pressed against the 

 canine and implanted obliquely to the long axis of the jaw. Naturally, 

 one is tempted to regard this species merely as the male of D. majttscuhis, 

 but the differences in the upper molars can hardly be of a sexual nature. 



In the table. No. 83 is a cast of the type of D. robustus and No. 85 of 



the type of D. coelops. 



Measurements. 



No. 83. No. 85. 



Upper dentition, length . . . . . . . . . . .148 



" incisor, greater diameter . . . . . . . . .011 



" " lesser " OIO 



" premolar-molar series, length . . . . . . . . .118 



Diastema between i^ and p^ . . . . . . . . . .019 



Upper premolar series, length ......... .0625 



Pl, length (z. e., antero-posterior diameter) . . . . . . .013 



" width (?'. e,. transverse diameter) ....... .0105 



P^, length OIS5 



" width 017 



P^, length 017 



" width 0205 



