406 
PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
Mi, antero-posterior diameter ..... 
“ transverse “ ..... 
M-i, antero-posterior “ ..... 
“ transverse “ 
Median inferior incisor, width of crown 
Lateral “ “ “ “ “ ... 
Lower canine, antero-posterior diameter at alveolar border 
“ “ transverse “ “ “ “ 
Anterior inferior premolar, antero-posterior diameter . 
tt 
ft 
tt 
transverse 
Median 
(1 
a 
antero-posterior 
it 
tt 
it 
transverse 
Posterior 
tt 
a 
antero-posterior 
i < 
a 
a 
transverse 
My, antero-posterior diameter 
(( 
transverse 
a 
m ¥ , 
antero-posterior 
ft 
it 
transverse 
tt 
M ¥ , 
antero-posterior diameter 
if 
transverse 
tt 
M T , 
antero-posterior 
tt 
it 
transverse 
1 1 
Patella, width ...... 
Terminal phalanges, average length . 
“ “ “ width of hoods 
.006 
.0057 
.002 
•0055 
.0015 
.002 
.004 
.003 
.0045 
.0016 
.0055 
.002 
•0055 
.0023 
.0058 
.0025 
.0062 
.003 
.0064 
.003 
.0065 
.0035 
.007 
.0065 
.003 
RELATIONSHIPS OF THE THYLACYNIDHL 
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. 
1. 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 Thylacynus, “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 
