30 SALT-WATER FISHES 



hindrance, the wonder is rather that almost all our sea fish are 

 not of cosmopolitan distribution. We know, however, that 

 such is far from being the case, and that not only do the 

 fishes of Australia, some of which have been already referred 

 to, differ materially from those of the northern hemisphere, 

 not only do the sea fish of the eastern and western shores of 

 the North Atlantic differ in an almost equally surprising 

 degree, but actually that there are fishes, like the torsk 

 (Brosmius)^ which occur in Scotch waters, but are not found 

 in the English Channel. 



The case of three of our smallest and least known British 

 flat-fishes, the topknots (Zeugopterus)^ may be taken as con- 

 veniently illustrating the peculiarity of an overlapping range. 

 One of these (^Z. punctatus) is found from the most northern 

 waters of Europe to only as far south as the Bay of Biscay. 

 Another (Z. unimaculatus) does not range farther north than 

 Shetland, but, on the other hand, it is met with as far south 

 as the Mediterranean. A third (Z. norvegicus), with ap- 

 parently the most restricted range of all, extends only from 

 the English Channel to the Norwegian fjords. Now, why one 

 or other of these topknots should never, at any rate in 

 sufficient numbers to occur in the trawl of commerce or 

 in the dredge of scientific expeditions, wander out of these 

 well-defined bounds, is a question that it would not be easy 

 to answer offhand. The mere question of temperature will 

 not, as may be seen by reference to the latitudes in question, 

 suffice as an explanation. 



Cases of irregular distribution are not, as might be 

 expected, uncommon, an unusual supply of food being 

 probably responsible in most cases. The case of quantities 

 of hake * (Merlucciuj) appearing one summer on the Cornish 

 coast has been explained on the ground of their pursuing 

 into those waters numbers of a small fish of the same 



* For another case of irregular occurrences of this fish sec Scan- 

 dinavian Fishes, p. 519. 



