ISOPROEDRIUM 85 
down in that region. Pm. I is represented by a moder- 
ately large alveolus, 10 mm. long. Pm. 2 is 13 mm. long 
by 10 mm. wide, and slightly constricted medianly as far 
as the enamel is concerned, the furrow in either side being 
filled with cement. Pm. 3 is 18 mm. long by 12 wide and 
similar. There is only an alveolus for pm. 4, which is 
23 mm. long. M. I is incomplete, but was about 23 mm. 
long by 10; mm. wide and is distinguished by the deep 
outer inflexion. Each tooth present is covered with a 
heavy layer of enamel nearly a millimeter thick; and each 
of the teeth is unique in that the enamel is wanting on 
the anterior internal and the posterior internal corners of 
the teeth. 
