598 THE OCEAN WORLD. 
Volga, the Elbe, and many of our own rivers. Jn some of the Irish. 
rivers the masses of shad taken in the seine-net have been so great 
that no amount of exertion has been sufficient toland them. It some- 
times attains a very considerable size, weighing as much as from four to 
six pounds. The shad taken at sea are less delicate in their flesh than 
those caught in fresh-water. The habits of the shad are very im- 
perfectly known. Two varieties are found on the British coast, 
‘namely, the Twaite Shad of Yarrell, which is about fourteen inches in 
length, brownish-green on the back, inclining to blue in certain lights, 
Fig. 383.—The Common Shad (C. alosa). 
the rest of the body silvery white, with five or six dusky spots on each 
side, arranged longitudinally, the jaws are furnished with distinct 
teeth, the tail deeply forked; and the Common or Allice Shad, 
which is considerably larger, sometimes attaining twelve and even 
fifteen inches in length, having only one spot on each side of the body 
near the head ; the jaws are without teeth, and the scales are small 
in proportion. This species is plentiful in the Severn, but rare in the 
Thames. 
The Twaite shad is found in the Severn and Thames in con- 
siderable quantities about the second week in July. They reach 
the fresh water about May, deposit their spawn, and return to salt 
water in July. Their scales are large. 
