THE TRUE FISHES. 163 
Virgin, off Block Island, was about seventy feet in length. 
They are harmless, living upon small pelagic animals that 
are strained into the throat through a series of hard, elastic, 
whalebone-like fringes, that are arranged comb-like along 
the large’ gill-openings. The teeth are small and compara- 
tively useless. The RAznodon (Fig. 199) is a similar form 
of East African waters, and attains a length of sixty or 
seventy feet. The mouth opens on a level with the snout. 
When struck, they have been known to carry large boats 
beneath the surface. 
VALUE OF SHARKS.—They are all scavengers. The skin of dog- 
fish and others is used as leather and shagreen. The oil of nearly all 
the species is valuable, and the bodies as guano. The teeth of sharks 
are used as weapons by the Pacific islanders. In China the shark-fin 
trade is an important one, they being used as food. 
Saw-Fishes (Pristide).— These remarkable fishes 
(Fig. 200) attain a length of fifteen feet, and are common 
on the North American coast from Cape Cod southward. 
Fic. 200,—Saw-fish. 
The snout is prolonged into a sword, the edges being 
armed with sharp, bony teeth. A species of saw-fish lives 
in a fresh-water lake in the Philippine Islands. The saw 
is used as a weapon by some tribes. They are vivipa- 
rous. 
Skates (aiaide).—These fishes are all notable for 
the development of the side or pectoral fins that in some 
species appear like wings. Their teeth are grinding plates, 
adapted for crushing mollusks and crabs. Their eggs are 
deposited in a dark, rectangular, parchment-like case, hav- 
