52 THE PROBLEM OP DISPERSAL 



water. Practically it is a hake, and at a remote period 

 probably was a marine fish. But at the time when it 

 acquired the exclusively fresh-water habit there must 

 have been terrestrial connection between Europe and 

 America, for the burbot is now the same in both these 

 continents, though it does not extend into Asia. It is 

 everywhere very local, but in England its distribution 

 points distinctly to an arrangement of sea and land very 

 different to that now prevailing. The burbot is found 

 only in the Trent, the Ouse, and certain other eastward- 

 flowing rivers and their tributaries. It was formerly 

 abundant in the Thames, but it is doubtful whether it 

 still survives in that river, and it never was in the Severn 

 or Wye. When this fresh-water cod first found a home 

 in these waters the German Ocean was a plain, through 

 which ran northwards a mighty river, known in its present 

 truncated condition as the Ehine, but then receiving 

 affluents from the eastern English watershed. Hence it 

 is easy to trace the connection between the burbots of 

 the Rhine and those of our Staffordshire brooks. 



Obvious as the identity is between some American and 

 European species, there are some remarkable discrepancies 

 in the fresh- water fauna of the two continents. The great 

 carp family is numerously represented in both, but of this 

 the genera of barbel and loach are entirely absent from 

 the New World. Europe and Asia together number about 

 two hundred species of barbel and fifty species of loach. 

 Of the last, the modest little fish that lurks under stones 

 in English woods and Scottish burns, never exceeding and 

 seldom attaining a stature of five inches, has a romantic 

 family history, could it only communicate the same. 

 Briefly, it is found in Japan, has not been recorded from 



