1. SALMO. 59 



its root from the vent ; its innermost ray is vertically opposite the 

 eleventh of the dorsal tin. Caudal strongly emarginate. 



There are 124 transverse series of scales, counted immediately 

 above the lateral line ; that descending obliquely backwards from 

 the origin of the dorsal fin consists of twenty-seven scales ; that 

 from the hinder end of the adipose forwards to the lateral line has 

 thirteen scales ; and there are twenty-four longitudinal series be- 

 tween the lateral line and the root of the ventral. All the scales are 

 rounded behind. 



Back brownish green, fading into silvery on the beUy; thickly 

 scattered over with black X-shaped or reticulated spots, each abo\jt 

 the size of four scales. A series of bright orange-coloured spots runs 

 along the lateral line, and a few are scattered on the lower part of 

 the sid'^8 ; the black spots are distinct and numerous on the opercular 

 bones, and very numerous and in many series on the dorsal fin ; 

 other fins immaculate and pale-coloured ; dorsal with a black and 

 yellow supero- anterior margin ; pectoral and ventral yellow • anal 

 with a black and yellow antero-inferior margin. 



4. Salmo fario. 



Among the numerous variations of the River-Trout, two forms 

 deserve particular attention : one, with fifty-seven or fifty-eight 

 vertebrae, is found in Central Europe and the southern parts of 

 England ; the other, with fifty-nine or sixty vertebrae, inhabits the 

 northern parts of Europe, certain parts of Scandinavia, Scotland, 

 and Iceland, In Cumberland, some of the rivers (Caldew, Eden) 

 are inhabited by the southern form, whUst the northern one is found 

 in the River Liddel. However, the latter extends as far southwards 

 as Shropshire, where both forms are met with. Both are subject to 

 the same amount of variation ; but the northern form appears to re- 

 main within smaller dimensions. The coincidence of the difierence in 

 the number of vertebrae with the geographical distribution appears to 

 be remarkable enough to distinguish the two forms ; but whether they 

 be regarded as species or varieties is a matter of minor importance. 



If we keep them separate, the question arises for which the name 

 of Salmo fario should be retained. Linnaeus, even if he had been 

 aware of the difference between the northern and southern forms, 

 would scarcely have distinguished them by different names. He 

 formed the name for Scandinavian and German River-Trout, refer- 

 ring especially to the Sahnonoid described by Artedi, who attributes 

 to it sixty vertebrae. Artedi also describes the caudal fin as emar- 

 ginate, having probably taken his description from a young example. 

 Thus the name of Salmo fario ought to be retained for the northern 

 form ; however, in a case like the present, when the boundary line 

 between species and variety is so obscure, I think it more convenient 

 to adopt a nomenclature indicative of the uncertainty existing. 



The synonymy also is often very uncertain, and the following 

 synopsis of synonyms probably contains several references to de- 

 scriptions taken from species distinct from S. fario. 



