GHAPTER Ex 
[SOTEMNIDAE 
Tuts family is distinguished by the formula $743, 
by the incisors, canine and premolar t all being of subequal 
size, by all the teeth being brachydont, and by the cres- 
cents of the lower premolars and molars being modified. 
On these lower premolars and molars the anterior crescent 
is longer than the posterior, and the short posterior cres- 
cent on the exterior of the tooth; so that its anterior horn, 
instead of uniting with the posterior horn of the anterior 
crescent, comes in back to about the middle of the anterior 
crescent. Then the pillar, which in the other families is 
situated in the posterior crescent, is opposite the posterior 
horn of the posterior crescent. The small animals which 
represent this family are rare in the Deseado beds, much 
more abundant in the Casamayor. ‘The family seems to 
have died out in the Deseado as no forms are referred 
to it in later epochs. We found no specimens belonging to 
the family; but to make this discussion complete, I will 
give a digest of Ameghino’s descriptions, with reproductions 
of such figures as he has given. All of the genera and 
species are based on very fragmentary material. 
The genera assigned to the family are Trimerostephanos, 
Pleurocoelodon, Lophocoelus and Henricofilholia. 
Trimerostephanos Ameghino 
Trimerostephanos Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 646. 
Trimerostephanos*Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 483. 
This genus is based on upper and lower teeth, and dis- 
tinguished by the premolars and molars having a weak 
style on the anterior corner, and by the anterior lobe being 
considerably larger than the posterior. Four species have 
been described. 
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