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 
SYOOGOE®) following measurements indicate the size, 
Pia ci lOWEE pin. 3'to Mm. 1, 25 mmi.; height of the 
pm. 3-m. I—natural size, 
after Ameghino. 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. 
