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FISHES OF THE CHALK. 
mode of their preservation, resemble the ichthyo- 
lites of Monte Bolca. 
Of the cartilaginous fishes, the teeth of several 
species of Squalus, or shark, are most frequent ; 
fins and vertebrae are also occasionally met with, 
but no decided examples of any other parts of these 
animals have hitherto been discovered. 
The usual varieties are figured below. The fossil 
FOSSIL TF.ETH OF SHARKS. 
1, 2. Teeth resembling those of Squalus Cuvieri. 
3, 4. Squalus Mustelus. 
5. Squalus Zygaena. 
6. Squalus, species unknown. 
7. Tooth resembling that of Squalus Perlon. 
palate teeth have hitherto been considered as belong- 
ing to a fish related to the Diodon ; they are more 
or less of a quadrangular shape, having the outer 
surface convex, and composed of an exceedingly 
hard enamel, which in the centre is formed into 
