252 BRITISH FRESH-WATER FISHES 



migratory trout of Great Britain. Dr. Giinther has catalogued 

 four separate species under the titles Salmo trutta^ S. cambricus^ 

 S. gallivensis, and S. brachypoma. On the other hand, Dr. Day, 

 while naming two — S. trutta and S. cambricus — considers that 

 the second is but the southern variety of the first. This is far 

 more nearly in accordance with the observation of unscientific 

 men accustomed to handle and sell these fish, but there remains 

 this difficulty in accepting Dr. Day's definition, that, whereas 

 his Salmo cambricus must be taken as intended to include what 

 is known in most parts as the bull-trout (6*. eriox of Linnaeus), 

 it is difficult to rate as a southern form a fish which is 

 peculiarly abundant on the coasts of Northumberland and 

 Berwick. 



The shape of the gill-cover, the arrangement of teeth on 

 the vomer, the number of caecal and pyloric appendages, the 

 number of vertebra, and the general appearance of these fish — 

 all of which are relied upon to indicate species — are so much 

 subject to variation, and blend so imperceptibly into inter- 

 mediate forms, that it is safest to hold judgment in suspense 

 for the present, and for practical purposes to maintain those 

 lines of distinction about which there is no manner of doubt in 

 the minds of experienced fishermen. It seems unnecessary to 

 go so far as H. Widegren did in 1863, and as later Continental 

 authorities have followed him in doing — namely, to reduce all 

 the European Salmones to two species, S. salar and ^S". trutta^ in 

 the latter of which he would group all trout, whether regularly 

 migratory and maritime in habit or not. Even if the dominant 

 races of British trout be ultimately proved to be convertible, 

 under uniform treatment and environment, to a single type 

 (which I am far from denying to be possible, and even 

 probable), it seems almost pedantic to refuse specific titles ta 

 thoses types which are perfectly distinguishable by appearance 

 and habit, and which have not yet been proved to be inter- 

 changeable. I shall therefore venture to define as the salmon- 

 trout {Salmo trutta) the fish known in Ireland as the white 



