i9°5-] 



SINCLAIR— FAUNA OF SANTA CRUZ BEDS. 



12. An alisphenoid bulla present in some genera, absent in 

 others. Tympanic annular and unfused with the adjacent elements 

 in the former, unknown in the latter. 



13. Basisphenoid perforated by internal carotid artery. 



14. Presence of avascular foramen (the post-zygomatic of Cope) 

 perforating anteriorly the base of the zygoma below or within the 

 lip of the post-glenoid foramen. 



15. Presence of a large vascular foramen (the sub-squamosal of 

 Cope) perforating the squamosal on or above the crest which con- 

 nects the base of the zygoma with the inion. This is absent in the 

 placental carnivores. 



16. Sutures of the skull distinct. Not strictly a marsupial char- 

 acter, but indicative of marsupial affinities when considered in con- 

 nection with the other characters presented. 



The four best known genera may be arranged as follows : 



A. Skull brachycephalic. Alisphenoid not dilated to form an auditory bulla. 



I. Dental formula |, i, |, |- Protocone on upper molars reduced. Mi 

 biscuspidate with paracone and antero-external style. Posterior pre- 

 molars greatly enlarged. Talonid of M T with single conical cusp. 

 Terminal phalanges round, blunt, and broadly fissured at the tips. 



B. Skull dolichocephalic. Borhycena. 



(a) Alisphenoid bulla absent. 



1. Dental formula | ? , i, f,|- Protocone well developed on M 1 and M-, 

 reduced on 1VP-. Mi with vestigial protocone and metacone. Poste- 

 rior premolar not greatly enlarged ; in the inferior series not exceeding 

 the median premolar in size. Talonid of M T small and basin-shaped. 

 Terminal phalanges laterally compressed, sharply pointed, and slightly 

 cleft at tips. Prothylacynus . 



(b) An alisphenoid bulla. 



1. Dental formula |, i, |, |. Protocone well developed on M i- ^-. Mi 



with small conical protocone, large paracone and antero-external style ; 

 metacone reduced to the merest vestige or absent. Premolars increas- 

 ing regularly in size posteriorly in both upper and lower series. 

 Talonid of M T enclosing a small basin-shaped area, unicuspidate. 

 Terminal phalanges uncleft, laterally compressed and pointed. 



Cladosiclis. 



2. Dental formula f, \, f, |- Protocone well developed on all the upper 



molars. Mi with protocone enclosing a basin-shaped area ; paracone 

 and antero-external style large ; metacone vestigial or absent. Upper 

 premolars increasing regularly in size posteriorly ; median and posterior 

 lower premolars subequal. Talonid in M T large and strongly bicuspi- 

 date. Terminal phalanges laterally compressed and pointed without 

 clefts. Amphiproznverra. 



