52 THE DESEADO FORMATION OF PATAGONIA 
The two crescents are markedly separated by a cleft from 
the external side of the tooth, opposite to which is a high 
denticle, made by the fusion of the two ends of the cres- 
cents where they come together. 
Proadianthus excavatus Ameghino 
P. excavatus. Amegh., loc. cit. above. . 
The species is based on the two lower 
premolars described above. I reproduce 
the figure given by Ameghino. The 
measurements are: length of pm. 3 and 
Fig. 23. Lower right 
4, 10 mm.; height of mandible under pm. pm. °3 and 4—natural 
size, after Ameghino. 
A,°O mim. 
