54- 



SIIARKS A 



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 

 from the warmer seas : and there are likewise certain extinct generic types. 



THE ELECTIUC RAYS, Family T 



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 



PO\V<T ]" derived inking the form of a series of vertically-placed prisms, situated 



on each -id*- of the front of the disc between the head and the pectoral fins. In 



addition to tin; distinctive,' feature, these ravs are, characterised by the broad and 



>th disc, in which the rays of the pectoral tins do not extend in advance of 



;i ^<- of the mu/y.]e. while the median fins are well developed. The family is 



