PRIMITIVE MACRAUCHENID 41 



Protheosodon Ameghino 



Protheosodon, Amegh., 1897, Bol. Inst. Geog. Argen., t. 1 8, p. 453. 

 Protheosodon, Amegh., 1904, Anal. Mus. Nac. B.A., ser. 3, t. 3, p. 421. 



This genus was founded on an upper second molar and 

 the fourth premolar. I figure m. 2, and it will be seen that 

 they represent a form little specialized, resembling in the 

 low crowns, plump cusps, and presence of both protoconule 

 and metaconule, the Casamayor types, such asLambdaconus 

 or Didolodus, rather than the advanced type like the Santa 

 Cruz genus, Theosodon. We found a specimen with the 

 lower jaws complete and with the hind limb complete, 

 which, I am confident, is the same form, though I can not 

 duplicate any tooth, for we found no upper teeth; but in 

 size they agree with Protheosodon, also in the primitive 

 character; and, were one from the lower teeth to postulate 

 the upper, they would be just such as Ameghino has de- 

 scribed under the name Protheosodon. Therefore I have 

 assigned my material to this genus and species. It adds 

 to the genus characters the fact that this form had a shorter 

 back, relatively as well as actually, than Theosodon; that 

 the hind limb, at least, was much heavier and also shorter 

 than that of Theosodon, especially in the metatarsal region 

 where relatively the elements are only about half as long. 

 The pes is of the same character as in Theosodon, but again 

 relatively much shorter. I believe in Prothesodon we have 

 to do with a form intermediate between Lambdaconus and 

 Theosodon, and nearer to the former. 



Protheosodon coniferus Ameghino. 



P. coniferus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 453. 



Ameghino has described two upper teeth. Specimen 

 No. 3001 of the Amherst Collection from the Chico del 

 Chubut River, west of Puerto Visser, adds to this the 

 knowledge of twelve vertebrae (seven dorsal and five lum- 

 bar), the lower dentition complete, the left hind limb 



