1862.] DR. A. GiJNTHER ON THE BRITISH CHARRS. 43 



I had no opportunity of examining), as he speaks of the Charr of 

 England and Ireland. M. Agassiz opposes those naturalists who, 

 for distinction of the species, have especially attached themselves to 

 the form of the head and to the arrangement of the colours, and says 

 that the characters ought to be found in the structure of the head, 

 in the opercular bones, in the surface of the cranium, and in its pro- 

 portions relative to the vphole body, and that the shape of the body 

 also is important for the distinction of the species. "When we add 

 the size of the teeth and of the scales, characters as constant and 

 excellent as any of those named, every one who peruses the descrip- 

 tions terminating this paper will satisfy himself that our three Bri- 

 tish species have been distinguished from one another and from those 

 of the Continent by those very characters which have been recom- 

 mended by M. Agassiz. Ichthyology has been so much advanced 

 within the last thirty years that it would be hardly fair to take the 

 same view of a paper written in 1834 as if it were of a recent date ; 

 and I make these lengthened remarks only because there may still 

 be some who, having adopted M. Agassiz's former views, will be in- 

 clined to adhere to them. 



When M. Agassiz denounces the form of the head and the arrange- 

 ment of the colours as too variable to supply precise characters, I 

 can only partly agree with him. With regard to the former, it is 

 only the snout which varies in its form according to age, sex, and 

 season ; but, according to my experience, this variation is subject to 

 certain laws : if a male of a certain age has a hooked prominent lower 

 jaw at a certain time of the year, all the males of that species, of the 

 same age and at the same season, are provided with a hooked man- 

 dible ; and this character may be well used as a specific distinction 

 from another species without such a hook. Differences in the shade 

 of colours are of no value for distinction of species. Sharply defined 

 markings, as cross-bands, large spots, may be dependent on age, and 

 peculiar to the young state of all the species of a whole group (dark 

 cross-bands in the genus Salmo equivalent to the white streaks in 

 the genus Sus, to the white spots in the genus Cervus, to the dark 

 spots in the young Lion, to the light dots in Muscicapa, Rubecula, 

 &c.) ; yet two species may differ, and really diifer, in the develop- 

 ment of those colours, and then they become a precise and valuable 

 character, which is nearly always joined with another. By the co- 

 lours alone, fresh specimens of (S. salvelinus and >S. umbla, of S. grayi 

 and S. willoughbii, may be always distinguished. 



Agassiz's view was adopted by Sir W. Jardtne*, who, however, 

 prefers to adopt another Linnean name, S. alpinus. He ascertained 

 its occurrence in most of the lochs of the north-west of Sutherland- 

 shire. 



1835. jENYNsfadopts only a part of the view advocated by Agassiz, 

 distinguishing a S. umbla and a S. salvelinus. With regard to the 

 former it is not stated whence the specimens had been obtained which 

 served as types for the description. " The elongated form, the gill- 



* Report of the Fourth Meeting of the British Association, at Edinburgh, p. 614 

 t Man. Hist. Vertebr. pp. 427, 428. 



