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 2043* <tne 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 

 species is distinguished by 



Fig. 13. Upper pm. 3-m. 3 of the left side 



its size primarily. The fol- 

 lowing are the chief measurements given. 



Upper dentition, pm. 3 to m. 3, length 50 mm. 



Lower dentition, inc. I 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 

 it is 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 Lambdacomis, though it 

 doubtless belongs to the series which is represented in the 

 Santa Cruz by Theosodon. He has also made a second 

 genus, Conioptothermm, 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. 



