THE SHARKS AND RAYS loi 



beneath. The spines before the dorsal fins are to be dreaded 

 only when the fish is carelessly handled, as in removing it 

 from the hook, when the smaller examples will writhe like 

 snakes and suddenly whip one of the spines into their captor's 

 wrist, inflicting a painful, though not envenomed, wound. 

 The teeth have a cutting inner edge, with the result that 

 these sharks bite through stouter lines than others of their 

 size. Picked dogs grow to a length of at least 4 ft. in 

 our seas, and at times they swarm on the fishing-grounds to 

 such an extent that neither the nets nor long lines can be 

 used to any purpose until their shoals have passed along the 

 coast. Although their razor-edged teeth enable them to bite 

 through even gimp snooding, it is noticeable that the picked 

 dogs take the hook without hesitation, showing none of the 

 tope's ingenuity in removing the baits. They are found in 

 the cooler seas of both hemispheres, but are said to be absent 

 from the warmer, though this is a statement that we may 

 look to see corrected by the results of future investigations. 

 They bring forth living young, and Dunn thought that they 

 had no fixed breeding season, but that also would be some- 

 what contrary to the rule among our fishes, both elasmo- 

 branchs and telesoteans. It is more commonly eaten by both 

 men and fish than most of our sharks. 



Centrina salviani is a rare wanderer from the Mediter- 

 ranean, and only one or two examples have been recorded 

 on our coasts. Specimens are, however, occasionally brought 

 to our ports from remote grounds, and Mr. Calderwood, then 

 of the Plymouth Laboratory, has figured and described one 

 that was trawled off Vigo Bay.* Its rough skin was a 

 character of the example in question, and there is an interesting 

 difference in the dorsal spines ; for whereas both of those on 

 the spur-dog point towards the tail, only the back spine of 

 Centrina points in that direction, the front spine pointing to 

 the head. Like the rest of the family, Centrina has deep 

 * ite Journal of the Marine Biological Associatiofi for November, 1892. 



