PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 
1 88 
No. 
No. 
No. 
No. 
No. 
I 5 A 92 . 
15,000. 
15 , 336 . 
15,256. 
15,001. 
Mandible, length (excl. teeth) 
. .361 
•425 
.410 
.412 
.212 
“ of symphysis 
. .092 
.091 
.105 
•043 
width at i^ . 
. .065 
.076 
.065 
.042 
depth at pj . 
• -073 
.067 
.080 
•073 
■043 
“ “ << 
m3- . 
. .077 
.100 
.080 
.084 
height of condyle . 
. .191 
.203 
.202 
.203 
coronoid 
. .200 
.227 
•239 
width, angle to 
. .149 
.192 
•152 
.168 
The above measurements 
are taken, in 
nearly 
all cases, 
from the 
same 
individuals as those of which the tooth-measurements are given in the pre- 
ceding tables. No. 15,001 is a very young skull with all the milk- 
dentition in place and the first molar, above and below, in process of 
eruption ; this skull is not only very much smaller than the adult, but is 
differently proportioned, the cranium being relatively longer and broader 
and the face shorter. Of the six adult skulls measured, one, No. 15,135, 
is very much smaller than any of the others and may possibly belong to a 
different species, though the evidence is insufficient for such a distinction. 
The mean basal length of the other five skulls is .435 M. and the skull in 
question is only 17 per cent, shorter than this average length. Even from 
the largest of the series, No. 15,141, it differs by only 20 per cent, and 
such differences are well within the limits of fluctuating variability, as 
determined by the measurements of many existing species. On the other 
hand, what suggests the possibility of a specific difference, is the isolated 
position of the small skull, which is not connected with those of the usual 
size by numerous intergradations. Nor would this result be materially 
changed if the measurements of the numerous skulls in the Princeton and 
New York collections were cited, the series in the table being sufficiently 
representative. 
Bones of the axial and appendicular skeleton are adequately known 
only in the present species and the account of them in the generic 
description has been drawn entirely from N. imbricatus. In the abun- 
dant material there is no complete individual skeleton, though almost all 
the skeletal elements are represented in the collection. Among these 
elements there is considerable variation in size and also, in certain cases, 
some well marked differences in structural features, but, unfortunately, it 
is not yet practicable to associate these differences with peculiarities of 
