76 LOWER VERTEBRATES. 



prickles, like those on a bramble, and, like them, leaving a scar when detached.' It is 

 a ground shark, rarely coming to the sui-face. 



The sleeper shark, Somniosus inicrocephala, is rather more common than the species 

 just mentioned, but still it is rare. It is properly an inhabitant of the Arctic regions, 

 and but rarely strays as far south as Cape Cod or the British Isles. Its length varies 

 between eisjht and twenty feet, and in weight it may reach two tons or more. Its 

 color is a purplish gray, with numerous white spots scattered over its surface. In the 

 Arctic regions it is more common, " and, although it never, or but rarely, attacks man, 

 it is one of the greatest enemies of the whale, which is often found with large pieces 

 bitten out of its tail by this shark. Its voracit)' is so great, that, according to Scores- 

 by, it is absolutely fearless of man while engaged in feeding on the carcass of a whale, 

 so that it can be pierced through with a spear or knife without being driven away. It 

 is stated to be viviparous, and to produce about four young at a birth." On our coast 

 it often comes near fishing-smacks, and feeds on the offal thrown overboard. Occa- 

 sionally a specimen is taken on a line and exhibited in the seaport towns. By the 

 fishermen it is known as ground-shark or gurry-shark, the word 'gurry' being a local 

 term for fish offal. 



Scymnus, the typical genus of the family, is represented by a single species in 

 European seas, while Isistius and Euprotomicrus are pelagic genera of tropical seas, 

 of which but little is known. 



The family Spinacid^ embraces the forms known as dog-fishes ; its members are 

 characterized by the absence of an anal fin, the presence of two dorsals, each bearing a 

 spine in front, the gill-slits five in number, the spiracles moderate, and the third eyelid 

 is absent. Among the internal peculiarities it may be mentioned that the centra of 

 the vertebrae and the intervertebral tissue are distinct, and the vertebrai are strongly 

 amphicoelous. About fifteen small species are known, mostly occurring in the Atlantic, 

 and divisible into six genera, three of which are re]iresented on the eastern coast of 

 the United States. 



Centroscylliimi fahricii, the black dog-fish, belongs to the Arctic seas, and thence 

 extends its range south to Massachusetts Baj'. In this southerly portion of its habi- 

 tat it is rare, but specimens have been taken off Gloucester by the members of the 

 United States Fish Commission. In Centroscyminis the dorsal spines are small, and 

 sometimes hidden beneath the skin. Nine species are known ; one from the East 

 Indies, the rest from the seas of Europe. One of these species, C. ccelolepis is caught 

 off the coast of Portugal, in water from four to five hundred fathoms in depth. The 

 fishermen use lines about six hundred fathoms long. Living at this great depth and 

 its conse(p;ent pressure, they are killed by being drawn to the surface, and, when the 

 fishermen take them into the boats, they are already withoxit power of motion. The 

 average length of this species is about four feet. 



Our common dog-fish of the north-eastern Atlantic coast has a wide distribution, 

 for it is found in Europe, while Dr. Gunther regards the Californian Squalus sucMii 

 as the same species. On our coast it bears several common names ; picked dog-fish, 

 bone-dog, skittle-dog, and hoe, while in scientific lore it is almost equally favored ; 

 though now the old name (Squuhis acanthias) given it by Linn6 is restored. In color 

 it is a gray or slate above, and lighter and even white beneath; in length it varies 

 from one to three feet; and in weight from five to fifteen pounds. It is common on 

 the coasts of Maine and Massachusetts ; and on Ca]ie Ann, at Boothbay, and other 

 places there are fishermen who make it their sole business to fish for them. Indeed, 



