210 The True Sharks 
limp. For these Garman has proposed the generic name Mala- 
corhinus, a name which may come into general use when the 
species are better known. In the deep seas rays are found 
even under the equator. In the south-temperate zone the 
species are mostly generically distinct, Psammobatis being a 
typical form, differing from Raja. Duscobatus sinensis, com- 
mon in China and Japan, is a shagreen-covered form, looking 
like a Rhinobatus. It is, however, a true ray, laying its eggs 
in egg-cases, and with the pectorals extending on the snout. 
Fossil Rajidg, known by the teeth and bony tubercles, are 
found from the Cretaceous onward. They belong to Raja and 
to the extinct genera Dynatobatis, Oncobatis, and Acanthobatis. 
The genus Arthropterus (rileyi), from the Lias, known from a 
large pectoral fin, with distinct cylindrical-jointed rays, may 
have been one of the Rajid@, or perhaps the type of a distinct 
family, Arthropterida. 
Narcobatide, or Torpedoes.—The torpedoes, or electric rays 
(Narcobatide), are characterized by the soft, perfectly smooth 
Fie. 151.—Numbfish, Narcine brasiliensis Henle, showing electric cells. 
Pensacola, Fla. 
skin, by the stout tail with rayed fins, and by the ovoviviparous 
habit, the eggs being hatched internally. In all the species is 
developed an elaborate electric organ, muscular in its origin 
and composed of many hexagonal: cells, each filled with soft 
fluid. These cells are arranged under the skin about the back 
