30 THE DESEADO FORMATION OF PATAGONIA 
LITOPTERNA 
This order of South American ungulates is less abun- 
dantly represented in the Deseado formation than in the 
Santa Cruz, but most of the genera of this latter formation 
have representatives in the Deseado so that they seem to 
have diverged still earlier. 
By Scott the order is divided into two families, the 
Proterotheriidae and the Macrauchenidae, the less known 
Adiantidae being placed under the latter family until 
better known. I feel that I should prefer to retain the 
Adiantidae for the present, until they can be shown to be 
subordinate to another family, so that in this paper the 
three families are retained. The striking features of the 
two larger families may be best brought out by a compari- 
son of their chief features as follows. 
Proterotheriidae 
NOMS 
2043 
Formula 
Upper inc. 2 and lower inc. 3 enlarged 
and tush-like, growing from  per- 
sistent pulps. 
Nasals normal 
Neck short. 
Feet with median digit enlarged, lat- 
eral digits reduced. 
Macrauchenidae 
eiges) 
3 043 
Incisors, canine, and premolar 1 
simple, compressed, subequal in 
size, and rooted. 
Nasals shortened indicating a pro- 
boscis. 
Neck long. 
Feet with all three digits subequal in 
size. 
Proterotheriidae Ameghino 
In the Deseado, this family is scantily represented as 
compared with the rich fauna, both as to species and num- 
bers of individuals in the Santa Cruz, but of the four chief 
genera of the Santa Cruz, three have been found, though 
the remains are very fragmentary. They are the genera 
Eoprototherium, belonging to the Prototherium series, 
Deuterotherium belonging to the Thaotherium series, and 
Notodiaphorus representing the Diadiaphorus series. 
