318 FISHES. 



the arctic and sub-arctic oceans. The others inhabit tem- 

 perate and tropical seas, and all attain to a very large size. 



Galbus. — Snout produced in the longitudinal axis of the 

 body ; teeth equal in both jaws, rather small, flat, triangular, 

 oblique, serrated and with a notch. Spiracles small. No pit at 

 the commencement of the caudal fin, which has a single notch 

 on its lower margin. 



These are small sharks, commonly called "Tope." The 

 species found on the British coast is spread over nearly aU 

 the temperate and tropical seas, and is common in Cali- 

 fornia and Tasmania. It lives on the bottom, and is very 

 troublesome to fishermen by constantly taking away bait or 

 driving away the fishes which they desire to catch. 



Zygmna. — The anterior part of the head is broad, flattened, 

 and produced into a lobe on each side, the extremity of which is 

 occupied by the eye. Caudal fin with a single notch at its lower 

 margin. A pit at the root of the caudal fin. Spiracles none. 

 Nostrils situated on the front edge of the head. 



The " Hammerheads," or Hammerheaded Sharks, have a 

 dentition very similar to that of Garcharias, and although 

 they do not attain to the same large size, they belong 

 to the most formidable fishes of the ocean. The pecuKar 

 form of their head is quite unique among fishes ; young 

 examples have the lateral extension of the skull much less 

 developed than adults. Five species are known, which are 

 most abundant in the tropics. By far the most common is 

 Zygmna malleus, which occurs in nearly all tropical and sub- 

 tropical seas. Specimens of this species may be often seen 

 ascending from the clear blue depths of the ocean like a 

 great cloud. Cantor found in a female, nearly 11 feet long, 

 thirty-seven embryons. — Hammerheads have lived from the 

 cretaceous epoch. 



MusTBLUS. — The second dorsal fin is not much smaller than 

 the first. No pit at the root of the caudal, which is without 

 distinct lower lobe. Snout produced in the longitudinal axis 



