212 



THE DESEADO FORMATION OF PATAGONIA 



talonid on the lower ones. Figure 138 gives a typical mar- 

 supial upper molar 2 and a lower molar 2 to show the sense 

 in which these terms are used. The Santa Cruz genera 

 are the best known and I therefore use them as a basis 

 for comparison with the less known Deseado forms, of 

 which \ve found but the one genus Pharsophorus at all 

 abundant. In addition to this, Ameghino has reported a 

 gigantic form designated Proborhyaena. The following 

 table indicates the relationships of the best known genera. 



From the foregoing, it will appear that Pharsophorus 

 approaches Borhyaena and Prothylacynus in the structure 

 of its upper molars, being, however, nearer to the former, 

 and the same is true of the structure of the talonid; but 

 Pharsophorus differs markedly from both in retaining the 

 metaconid as a small cusp on the side of the protoconid 

 on all of the lower molars; also in the extremely small size 



