PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
1 86 
Di 1 , length 
“ width .......... 
Upper milk-canine, length ....... 
“ “ “ width 
Upper milk-premolar series, length 
Dp-, length 
“ width .......... 
Dp-, length 
“ width .......... 
Dp-, length .......... 
“ width .......... 
Dp^, length .......... 
“ width .......... 
No. 15,001. 
. .013 
. .006 
. .014 
. .006 
. .087 
. .017 
. .009 
. .019 
. .017 
. .0265 
. .018 
• -033 
. .018 
No. 16,010. 
Lower milk-dentition, length 
. .108 
.118 
Diy, length 
. .009 
.007 
“ width .......... 
• 
.011 
Dig , length 
. 
.006 
“ width .......... 
. .013 
.013 
Di ¥ , length .......... 
. .005 
.008 
“ width .......... 
. .014 
.016 
Lower milk-canine, length . 
. .015 
.017 
“ “ “ width 
. .0045 
.006 
Lower milk-premolar series, length 
• -079 
.084 
Dpy, length 
. .017 
.018 
“ width .......... 
. .009 
.009 
Dpg, length 
. .019 
.019 
“ width .......... 
. .009 
.0095 
Dp ¥ , length 
. .021 
.023 
“ width . . . . . . . . . 
. 
.010 
Dpy, length 
. .026 
.026 
“ width .......... 
. .012 
.Oil 
My, length . . 
.030 
No. 15,001 is the skull of a very young animal, in which the first upper 
true molar (m-) is just beginning to erupt and shows no sign of abrasion, 
while the first lower molar (m T ) was already in 
partial use, 
the anterior 
crescent being slightly worn. No. 16,010 is the left ramus 
mandibuli of 
an older and larger animal, in which m T is quite fully erupted and both 
crescents are worn, indicating that the corresponding upper tooth was in 
function. Curiously enough, no traces of the germs of the permanent pre- 
molars are yet visible. Doubtless, the germs were present in the living 
jaw, but not calcified. 
