loo SALT-WATER FISHES 



species which finds its way from the Mediterranean to our 

 shores has six, but there is another in that sea with seven, and 

 this possession of more than five gill-openings may be regarded 

 as a sign of antiquity. 



The Six-gilled Shark {Notidanus griseus) is the straggler to 

 our coasts, where an example of over 26 ft. and others 

 of 6 and 1 1 ft. have been taken, mostly with baits. In 

 colour it is reddish grey ; the head is noticeably small for the 

 length of the body ; the upper lobe of the tail-fin is conspicu- 

 ously the longer, though there is a distinct lower lobe. The 

 eye lacks the nictitant membrane, and the small spiracle lies 

 some way behind it. As a further distinguishing feature, it 

 lacks the front dorsal fin found in all our other sharks, or 

 rather its single dorsal fin lies back near the tail. It is said to 

 be a voracious shark, and to produce living young ; but its 

 habits have been little, if at all, studied in our seas. 



Spinacidae 



The fifth family of sharks may be distinguished by the 

 deep, straight, generally oblique groove at the angles of the 

 mouth. This character seems fairly constant throughout 

 the genera, whereas the presence of spines in front of the 

 dorsal fins applies only to Acanthias and Centrina, doubt- 

 fully to Centrophorus (in which the skin overgrows them), anci 

 not at all to L,emargus and Echinorhinus. All the genera 

 have spiracles and narrow gill-openings, and all lack the anal 

 fin, while the eye is without nictitant membrane. 



The Spur-dog, or Picked Dog [Acanthias vulgaris), is one 

 of the commonest sharks in our seas, where it is easily 

 recognised, being in fact the only abundant form with spines 

 before the dorsal fins. Its colour is some shade of grey or 

 brown above (all these sharks vary in colour far more than 

 tJie bony fishes, though the accounts given by Day and Couch 

 often suggest certain colours as constant) and a lighter hue 



