CHAPTER III 



THE SHARKS AND 'BJlYS 



The precise relationship of the Sharks and Rays now living is 

 not by any means so clear as some writers pretend, and one 

 of the most recent of these has more cautiously admitted 

 a doubt whether the two groups are even descended from 

 a single palaeozoic ancestor.* The most ancient form in our 

 seas would seem to be the six-gilled shark {Notidanus), and, 

 with the exception of their having reduced their gill-openings 

 by one, it cannot be said that the rest have materially departed 

 from the type of this shark, beyond of course such specialising 

 as might from time to time be demanded by their surroundings 

 and mode of life. In following the usual course and treating 

 of the Sharks and Rays under one head, this chapter merely 

 avoids a somewhat more modern classification, in which the 

 spur-dog (^Acanthias) would be regarded as the transitional 

 link rather than the shark-ray (Rhina), because it could not 

 well be explained without digressing in the direction of com- 

 parative anatomy quite beyond the scope of the present 

 volume. For practical purposes it seems more satisfactory 

 to retain the older arrangement followed by Couch and Day, 

 with the Sharks and Rays abruptly subdivided, while at the 

 same time bearing in mind that the study of embryological 

 and other affinities has lately necessitated a revision of 

 their scheme. 



There is a deep-rooted conviction in circles otherwise 



* Bashford Dean, Fishes, Living and Fossil, p. 88. 



8+ 



