40 THE DESEADO FORMATION OF PATAGONIA 
both the upper and lower premolar and molar teeth. As 
far as it is known, it is distinguished by the upper molars 
lacking the metaconule entirely, and being approximately 
like those of Thaotherium. ‘The dental formula is given 
by Ameghino as ~34-, the same as Thaotherium. But 
one species has been described. 
Deuterotherium distichum Ameghino 
We did not find this species, but the teeth assigned to 
it are very characteristic, 
and so I reproduce Amegh- 
ino’s figure of them. The 
Et ise etka tae ee species is distinguished by 
natural size, after Ameghino. its size primarily. ‘The fol- 
lowing are the chief measurements given. | 
Upper dentition, pm. 3 to m. 3, length 50 mm. 
Lower dentition, inc. 1 to m. 3, length 80 mm. 
Macrauchenidae 
(= Mesorhinidae Amegh.) 
This family is distinguished, first, by the complete 
dental series in which none of the anterior teeth are devel- 
oped into tushes; by the nasals being shortened, apparently 
in connection with the development of a proboscis; by 
its long neck; and by its feet being permanently tridactyl, 
all the three toes being equally developed. In the Deseado 
itis infrequent, but to it Ameghino has assigned two genera; 
Protheosodon, which he describes as similar to Theosodon, 
but which I find much nearer to the Casamayor repre- 
sentatives of this family, such as Lambdaconus, though it 
doubtless belongs to the series which is represented in the 
Santa Cruz by Theosodon. He has also made a second 
genus, Conioptotherium, which represents a large Macrau- 
chenid, equal in size to Theosodon. ‘This genus is based 
on the calcaleum and astragulus and seems to be rare. 
