274 FISHES 



tropics. Of Acanthopterygians the chief families are Cottidse, 

 some of which reach a large size, Agonidae, Cyclopteridae or 

 lump-suckers and sea-snails, and Blenniidae. Characteristic 

 genera are Cottus or the bull-heads, Anarrhichas, the cat-fish 

 or wolf-fish, Cyclopterus, or lump-suckers, Centronotus or gunnels, 

 and Lycodes. Gadidae are also characteristic, especially species 

 of Gadits, including the cod, Brosmius, the tusk, and Mo/va, 

 the ling. The most northern of the Flat-fishes are Hippo- 

 g/ossus, the halibut, and species of Pleuronectes allied to plaice 

 and dab. Physostomi are scarce, and represented only by the 

 herring and a few other species of Clupea and by the salmonoid 

 Mallotus, the capelin, which occurs in extraordinary numbers 

 on the coasts of Greenland and Kamtchatka. Elasmobranchs 

 are scarce, Acant/tias, Ccntrosylliwu and a species of skate 

 being the only representatives ; CJiimaera also extends into 

 Arctic regions. 



The Antarctic fish-fauna shows a certain resemblance to 

 the Arctic, some of the species being the same. Agonidae and 

 Scorpaenidae occur as in the Arctic, two of the genera, Agonus 

 and Sebastes, being identical. Bull-heads (Cottidae) are absent 

 and in their place we find several genera of Nototheniidae 

 which, although in some species similar in appearance to the 

 bull-heads of the north, are allied to the weevers or Trachinidae. 

 Lycodes is found, but the lump-suckers and Arctic blennies 

 are absent. One or two species of Gadidae are found, namely 

 Lotella and Merluccius or hake, but not the genus Gadus. 

 Flat-fishes are scarce and belong to peculiar genera. Among 

 the Elasmobranchs AcantJiias vulgaris the common spiny dog- 

 fish is present and some species of skate {Raid) while Chimaera 

 is represented by the southern form CallorJiynchus. The re- 

 appearance of certain Arctic species in the Antarctic region 

 seems at first difficult to explain, but when we remember that 

 temperature is the most important barrier to dispersal, and 

 that there is a cold water connection between the waters of the 

 two poles through the deeper parts of the oceans it seems quite 

 possible that in the course of ages some specimens of an Arctic 

 species might pass the tropical zone by travelling at a sufficient 

 depth. 



Having thus pointed out the most important special 

 features of the extreme zones we shall not attempt to survey 



