406 PATAGONIAN EXPEDITIONS I PAL/EONTOLOGY. 



M&, antero-posterior diameter ......... .006 



" transverse " 0057 



M-t, antero-posterior " ........ .002 



" transverse " 0055 



Median inferior incisor, width of crown ....... .0015 



Lateral " " " " " 002 



Lower canine, antero-posterior diameter at alveolar border . .004 



transverse " " " " 003 



Anterior inferior premolar, antero-posterior diameter ..... .0045 



" " " transverse " ..... .0016 



Median " " antero-posterior " . . . . . -0055 



" " " transverse " ..... .002 



Posterior " " antero-posterior " ..... -OO55 



" " " transverse " . . . . . .0023 



M T , antero-posterior diameter . . . . . . . . . .0058 



" transverse " ......... .0025 



M^-, antero-posterior " ......... .0062 



" transverse " .......... .003 



My, antero-posterior diameter . . . . . . . . . ' .0064 



" transverse " ......... .003 



My, antero-posterior " ......... .0065 



" transverse " 0035 



Patella, width 007 



Terminal phalanges, average length ........ .0065 



" " " width of hoods ...... .003 



RELATIONSHIPS OF THE THYLACYNID^E. 



Although there is sufficient similarity in structure to warrant placing the 

 Patagonian and Tasmanian thylacynes in the same family, it must not be 

 inferred that the existing genus is the direct descendant of its extinct 

 South American forerunners. The study of the group has failed to show 

 a closer relationship than probable descent from a common pre-Santa 

 Cruz ancestor. While retaining the fundamental family characters, both 

 lines have diverged and in some respects the Santa Cruz forms are more 

 advanced than the existing genus. 



i. Without exception, the Santa Cruz forms, so far as known, show 

 great reduction of the external styloid cusps in the upper molars, the 

 antero-external style alone remaining, while in Tliylacyuns, "a small ele- 

 ment probably equivalent to style c 2 is apparently always present in the 

 first molar, variable in the second, and scarcely distinguishable in the 



