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 IJ therefore use them as a basis 
for comparison with the less known Deseado forms, of 
which we found but the one genus Pharsophorus at all 
abundant. Jn addition to this, Ameghino has reported a 
gigantic form designated Proborhyaena. The following 
table indicates the relationships of the best known genera. 
TALONID ON 
AGE FORMULA| PROTOCONE | UPPER MOLAR | LowER Mo- | SYMPHYSIS 
3 LAR 3 
Cladosictis Santa Cruz|_4 1 4 3 jon pm. 4—m. 3|Protocone Small basin |Ligamentous 
SAS Paracone vesti-| with one 
gal post. cusp 
Metacone 
Ant. ext. style 
Amphiprovivvera Santa Cruz) 4 ! 4 3 jon pm. 4—m. 3|Protocone Basin —_with|Ligamentous 
3143 Paracone two post. 
Ant, ext. style cusps 
Prothylacynus Santa Cruz) 4 1 4 3} onpm.4m.1|Protocone ves-|Small basin|Fused 
3143 tigal with one 
Metacone post. cusp 
Borhyaena Santa Cruz| 3 1 4 3 |vestical Paracone No basin Fused 
32143 Ant. ext. style |One post.cusp 
Pharsophorus Deseado I 4 3 |vestigal Protocone ves-|Very small |Ligamentous 
143 tigal No basin 
Paracone One post.cusp 
Ant. ext. style 
Proborhyaena Deseado i? Fused 
143 
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 
