28 C 
FOSSIL SHARKS. 
mation as nearly coinciding with that of the 
Oeningen deposits. 
The Fishes of the Crag of Norfolk, and the 
superior Sub-apennine formation, as far as they 
are yet known, appear for the most pait related 
to genera now common in tropical seas, but are 
all of extinct species. 
Family of Sharks. 
As the family of Sharks is one of the most 
universally diffused and most voracious among 
modern Fishes, so there is no period in geolo- 
gical history in which many of its forms did not 
prevail.* Geologists are familiar with the occur- 
rence of various kinds of large, and beautifully 
enamelled teeth, some of them resembling the 
external form of a contracted leech, (PI. 27', 
and 27^) : these are commonly described by the 
name of Palate bones, or Palates. As these 
teeth are usually insulated, there is little evi- 
dence to indicate from what animals they have 
been derived. 
In the same strata with them are found large 
bony Spines, armed on one side with prickles, 
resembling hooked teeth, (see PI. 27“. C. 3. a.) 
These were long considered to be jaws, and 
true teeth ; more recently they have been ascer- 
* M. Agassiz has ascertained the existence of more than one 
hundred and fifty extinct species of fossil Fishes allied to this 
family. 
