TRICOELODUS 51 



Adianthidae Ameghino 



This family is based primarily on the genus Adianthus 

 of the Santa Cruz to contain some macrauchenid-like 

 forms which, however, are of much smaller size, and differ- 

 entiated by the narrow character of the teeth and their 

 early tendency to hypsodonty. It seems to be a valid 

 series of dwarf types, which are all scarce and known only 

 by the most fragmentary remains. Two genera are de- 

 scribed from the Deseado, Tricoelodus, peculiar in having 

 the posterior lobe of the lower molars somewhat subdivided 

 so that the tooth appears three-lobed; and Proadianthus, 

 known only by premolars which however show an unusual 

 development of the styles on the inner side of the teeth. 





 Tricoelodus Ameghino 



Tricoelodus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 454. 



The genus is based primarily on the three-lobed char- 

 acter of the molars, which is a secondary effect of an infold- 

 ing on the inner side of the posterior lobe. They are rooted, 

 but strongly hypsodont. The margins of the crescents 

 are well developed and the ' 'pillar" is a prominent feature 

 in the posterior crescent. 



Tricoelodus bicuspidatus Ameghino 



T. tricuspidatus Amegh., loc. cit. above. 



The species is the only one known of the genus, and 

 its features are those of the genus. The 

 _ _ following measurements indicate the size, 



Tig. 22. Lower right lower pm. 3 to m. I, 25 mm.; height of the 

 mandible under molar I is 12 mm. 



Proadianthus Ameghino 



Proadianthus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 455. 



This genus is known only by the last two premolars of 

 the lower jaw, which are compressed and moderately high. 



