472 PISCES SUB-CLASS IILTELEOSTOMI. 



gullet, while the long and single dorsal fin has no distinct spinous portion. 

 The two genera are Stromateus arid Centrolophus ; one species of the latter 

 occasionally reaching the southern shores of Britain, where it is known as the 



black-fish. Of more importance is the family CforyfhcenidcK, 



Family which differs from the last by the absence of spines in the 



Coryphcenidce. gullet ; the teeth, when present, being small and conical. 



The typical members of the family are the pelagic cory- 

 phaenas (Coryphcena), commonly but incorrectly known as dolphins. These 

 are large brightly-coloured fishes, with the body rather elongated and some- 

 what compressed, the dorsal fin occupying nearly the whole length of the 

 back, the caudal very deeply forked, and the moderately long anal without 

 any distinct spinous portion. In the adults the head is ornamented with a 

 kind of crest. In the coryphsenas beauty is even less than skin-deep, the 

 exquisitely lovely colours being fugitive and transitory immediately the fishes 

 are removed from their native elements. The coryphsenas are highly preda- 

 ceous fishes, and in the Mediterranean and other warm seas may often be 

 seen in large companies pursuing the shoals of flying-fish. The only other 

 genus that can be mentioned here is Lampris, represented by a single very 

 beautiful fish from the Mediterranean and North Atlantic. Unfortunately, 

 this fish is commonly known as the sun-fish, a title also applied to the mem- 

 bers of the genus Orthagoriscus, mentioned in the sequel. Another instance 

 of such synonomy occurs in the use of the name barracuda, which is applied 

 indifferently to the species of the genera Thyrsites and Sphyrcena. In the 

 sun-fish, the whole body is very much compressed, short, and deep, the 

 scales being minute and deciduous, the mouth narrow and toothless, the 

 fore-part of the dorsal fin elevated to a point, and the pelvic fins including a 

 number of rays. In colour, the body has a bluish ground, upon which are a 

 number of silvery spots, while the fins are scarlet. In size, this splendid fish 

 grows to about four feet. 



From the allied families the small group of the Nomceidce is distinguished 

 by the differentiation of a distinct spinous portion, separated by a short 



interval from the soft portion of the dorsal ; the caudal fin 



Family being forked, while finlets are sometimes developed, and the 



NomcKid. scales are cycloid and of moderate size. Four genera are 



included in the family, of which the typical Nomceus has 

 representatives in the Indian and tropical portions of the Atlantic Ocean, 

 while Gastrochisma has one species from the New Zealand seas. 



Nearly allied to the last is the valuable family of the mackerels, in which 

 there are likewise two dorsal fins and generally finlets ; the body being either 



scaled or naked. The best distinctive features of the family 



Family are to be found in the conformation of the tins ; some forms 



Scomberidce. having the spinous dorsal modified either into separate spines 



or into a large sucker ; while when the former is normal the 

 soft dorsal and anal are split up into finlets. In form, the body is either 

 spindle-shaped or oblong ; and, internally, the air-bladder may be present or 

 absent. The mackerels are among the most highly organised of all fish, the 

 loss of the air-bladder in some forms being probably due to the exact corre- 

 spondence between the specific gravity of their bodies and that of the water, 

 which renders any adjustment unnecessary. They are mostly pelagic forms, 

 and their coloration is exactly in harmony with their environment, the 

 mottled greens and blacks of the back rendering them invisible from above 

 as they swim in the rippled waters, while their glistening silvery under- 



