80 LOWER VERTEBRATES. 



length of thirty feet. Its teeth are small, and it feeds principally on fish and other 

 marine animals, and but rarely attacks man. When ai-oused, it is a dangerous cus- 

 tomer, not so much on account of its teeth, as from the violent strokes of its tail, 

 which will break in the sides of a whale-boat. Its liver makes a large amount of oil, 

 six barrels havino- been obtained from a single shark. 



Considerable confusion exists concerning the species of Carcharias, from the fact 

 that the generic term has been used by different authors for greatly different sharks. 

 As here employed, it is the equivalent of the genus Odontaspis of some, while their 

 Carcharias, is, in the present work, the genus Carcharinics. But three species of the 

 genus are known. They are pelagic, and occur in the temperate and tropical seas, 

 C. americatms being the sand-shark, gray-shark, or shovel-nose of the Atlantic coast. 

 It is a small species, rarely exceeding six feet in length, but its size is in no way com- 

 mensurate with its appetite, it being one of the most voracious of all the group. It 

 may be separated from all others of this family occurring on our coast, by having 

 moderate-sized gill-openings, all of which are in front of the pectoral fins. In color 

 it is gray, and its teeth are sharj) and awl-shaped. 



The thresher shark, Alopias vulpes, is readily recognized by its extraordinarily long 

 tail, which forms over half the length of the whole animal. It is distributed in both 

 Atlantic and Pacific oceans, but, though occasionally taken in California and Xew Zea^ 

 land, it is much more common in the Mediterranean and on our eastern coasts. It is 

 a migratory shark, but its migrations are dependent upon the shoals of mackerel, men- 

 haden, herring, or other fish on which it feeds. " When feeding, it uses the long tail 



Fig. 62. — Alopias vulpes, thresher shark. 



in splashing the surface of the water, while it swims in gradually decreasing circles 

 round a shoal of fishes, which are thus kept crowded together, falling an easy prey to 

 their enemy. Statements that it has been seen to attack whales and other large ceta- 

 ceans rest upon erroneous observations." The powerful stroke it gives with its tail 

 explains the terms, thresher and swingle-tail, which are usually applied to it. It is 

 occasionally taken by the fishermen, but its powerful strokes render its capture a diffi- 

 cult matter, while the small amount of oil in its liver poorly rewards the labor neces- 

 sary to obtain it. It reaches a length of about fifteen feet ; above, it is bluish lead- 

 color, beneath, white. 



The Spheynedje embraces the hammer-headed sharks, the most peculiar of the 

 order. In most of their features they resemble the next family, the Galeorhinidae, 

 but their peculiar heads at once separate them. They have an anal fin, two dorsals 

 without spines, the first being behind the ventrals, and no spiracle ; the head is ex- 

 panded, on either side, into a broad lobe, and on the ends of these lobes the eyes are 



