180 THE DESEADO FORMATION OF PATAGONIA 
The lower jaws were associated with the above skull, 
and are complete to behind the third molars on both sides. 
They are very short and heavy, especially in the anterior 
portion, the symphysis extending back to opposite the 
middle of the second molar. The height under molar 3 
is 150 mm. See frontispiece. 
From the upper dentition, I give the measurements 
of my two chief specimens, together with those given by 
Ameghino for his type of P. sorondoi, and the figures 
given by Gaudry; from which may be seen the amount of 
variation which individuals may show. 
UprerR DENTITION SPECIMEN SPECIMEN AMEGHINO’S GAUDRY’S 
No. 3207. No. 3250 TYPE SPECIMEN 
Total length, inc. 1 to m. 3 530 mm, 
Inc. 1, length above alveolus — 133 mm. 
Inc. 1, antero-posterior diam. 49 mm. 
Inc. 1, transverse diam. 37 mm. 42 mm. 
Inc, 2, length above alveolus 174 mm. 
Inc. 2, antero-posterior diam. 59 mm. 77 mm, 65 mm. 
Inc. 2, transverse diam. 40 mm. 52 mm. 41 mm. 
Premolar 2, length 45 mm. 52mm. 48 mm. 40 mm. 
Premolar 2, width 36 mm. 40 mm. 30 mm. 29 mm. 
Premolar 3, length 46 mm. 49 mm. 48 mm. 40 mm. 
Premolar 3, width 57 mm. 57 mm. 46 mm. 48 mm. 
Premolar 4, length 47 mm. 51 mm. 46 mm. 43 mimi: 
Premolar 4, width 63 mm. 64 mm. 58 mm. 57 mm. 
Molar 1, length 55 mm. 55 mm. 57 mm. 55 mm. 
Molar 1, width 68 mm. 69 mm. 61 mm. 6r mm. 
Molar 2, length 63mm. 77 mm. 7oO mm, 57 mm 
Molar 2, width 85 mm. 93 mm. 75 mm. 68 mm. 
Molar 3, length 75mm. 68 mm. 83 mm. 64 mm. 
Molar 3, width 86 mm. 87 mm. 82 mm. 88 mm. 
For the lower dentition, I give the figures which Ame- 
ghino records for his P. sorondot, those given by Gaudry 
for his P. romert, and the measurements of specimen 
No. 3207. ‘The tushes in the lower jaw I would designate 
as incisors 2; because when the jaws are closed these diverge 
and their tips bite against the tips of the upper incisors 2. 
The first incisor seems to have been gradually lost and 
