542 
SHARKS AND RAYS. 
surface is brown, with numerous lighter spots, while beneath it is pure white. 
Fossil skates of this genus range through the Tertiaries to the upper Cretaceous. 
At the present day the family is represented by three genera, each with but few 
species, from the warmer seas ; and there are likewise certain extinct generic types. 
The Electric Rays, —Family Torpebinidje. 
In common with the electric eel, the members of this family are characterised 
by their power of communicating galvanic shocks; the organs from which this 
COMMON SKATE AND MARBLED ELECTRIC RAT (jC nat. size). 
power is derived taking the form of a series of vertically-placed prisms, situated 
on each side of the front of the disc between the head and the pectoral fins. In 
addition to this distinctive feature, these rays are characterised by the broad and 
smooth disc, in which the rays of the pectoral fins do not extend in advance of 
the base of the muzzle, while the median fins are well developed. The family is 
