SHARKS AND RAYS. 421 
Among the more aberrant sharks is the hammer-headed 
Sphyrna zygena (Linn.), which grows to the length of twelve 
feet, and is one of the most rapacious and formidable of the 
order. 
Of the rays and skates, the saw-fish approximates most 
to the sharks. Its snout is prolonged into a long, flat 
bony blade, armed on each side with 
large teeth. Pristis antiquorum 
Latham (Fig. 390), the common saw- 
fish, inhabits the Mediterranean Sea 
and the Gulf of Mexico ; it is vivipa- 
rous (Caton.) Pristis Perroteli lives 
in the Senegal River, while Carcharias 
gangeticus is found sixty leagues from 
the sea. ; 
The genuine skates or rays have the 
body broad and flat, rhomboidal (ow- 
ing to the great extension of the 
thick pectoral fins). Portions of the 
ventral fins in the males are so elon- 
gated and modified as to form intro- 
mittent and clasping organs. They 
swim close to the bottom, feeding upon 
. shell-fish, crabs, etc., crushing them 
with their powerful flattened teeth. 
The spiracle is especially developed in 
the rays, while, as observed by Gar- 
man, in the majority of the sharks 
which swim in midwater or near the 
surfacz, the water enters the mouth 
and passes freely out of the gill-open- 
ings, but in the rays, which remain at ™ 
Fig. 390.—Beak of Saw-fish, 
the bottom, the purer sea-water enters seen from below, showing its 
the spiracle from above to pass out of Bem ater owen” em 
the gill-slits. 
The smallest and most common skate of our northeast- 
ern Atlantic coast is Raja erinacea Mitchell. It is one half 
of a metre (twenty inches) in length, and the males are 
smaller than the females. The largest species is the barn- 
door skate, Raja levis Mitchell, which is over a metre (forty- 
