SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 347 



BORHY^ENA Ameghino. 



(Plates XL-XLVI ; LIT, Figs. 1,2,6; LIU, Figs. 2, 2, 4-46, g,ga; 

 LIV, Figs. 7, 13; LXI.Fig. 3.) 



Borhycena Amegh.; Enum. Sist. Especies Mamif. F6s. Patagonia Austral, 



p. 8, Dec., 1887. 



Dynamictis Amegh.; Revista Argentina Hist. Nat. I, entr. 3^, pp. 148- 

 149, June, 1891. 



A genus of large marsupial carnivores containing the most powerful 

 predatory mammals in the Santa Cruz fauna. In the Princeton collection 

 two species are represented by good skulls, with one of which a consid- 

 erable portion of the skeleton is associated. 



Dentition (Pis. XL; XLII ; XLIV; XLV, figs, i, 3). In both spe- 

 cies (B. tuberata, B. excavatd], the incisors are reduced to 3, a formula 

 unknown among existing marsupials, with the exception of Notoryctes. 

 The upper incisors here have been worn to such an extent that the pattern 

 of the crown is entirely obliterated. The median pair are laterally com- 

 pressed and show no tendency to assume a procumbent position or to be- 

 come approximated at the tips, suggesting that in Borhycena the reduction 

 of the superior incisor formula has been accomplished by the suppression 

 of the teeth homologous with the conical, procumbent, median incisors of 

 Didelphys and Dasynrus. The upper canine is large, with swollen root 

 and thick blunt crown. The premolars are closely crowded and increase 

 rapidly in size posteriorly. All are double-rooted. The anterior pre- 

 molar is in contact with the canine, and is placed transversely to the tooth 

 row. The crown is slightly compressed laterally, and the heel rounded, 

 without heel cusp. The median premolar is similar to the preceding 

 tooth, but carries a larger heel. The posterior premolar is greatly 

 enlarged and the heel broad, extending around the inner side of the 

 crown. The anterior margin of the tooth is more or less abraded by con- 

 tact with the similarly enlarged lower posterior premolar. The worn 

 molars bear a superficial resemblance to the teeth of Sarcopliilits, but 

 their thylacyne structure is fully apparent, when it is remembered that in 

 Sarcophilus the broadening of the upper molar cusps is produced by basal 

 fusion with the outer row of styles, of which the antero-external alone is 

 present in Boryhcena. The first, second and third molars increase regu- 

 larly in size posteriorly. The protocone is small and ledge-like; disap- 



