72 GUIDE TO THE FOSSIL EEPTILES,*AMPHIBIANS, FISHES. 
Wall-case Table-case in Gallery 10). The Carchariidae are almost, if 
3 - not exclusively, Tertiary, and only a small collection of the 
Table-case 17 
7 . 
Fig. 72. — Crown of tooth of the extinct 
Carcharodon megalodon , dredged by the 
“Challenger” from a depth of 2,385 
fathoms in the South Pacific Ocean 
nat. size. (See middle Table-case in 
Gallery 10.) 
teeth and vertebrae of Carcharias, G-aleocerdo, Hemipristis, etc., 
is exhibited (Table-case 7). 
Sub-ordek 2.— Tectospondyli. 
Wall-case The surviving spiny dog-fishes or Spinacidae seem most 
m , . 3 - nearly to represent the ancestors of the skates, but they are 
7 *8. only known to date back to the Cretaceous period. Acanthias 
and Centrophorus are represented by complete fishes in the 
Upper Cretaceous of Mount Lebanon (Table-case 7). The 
Pristiophoridae and Pristidae are proved to be of similar 
antiquity. Sclerorhynchus from Mount Lebanon is an 
