INTRODUCTORY 19 



and particularly those of the genus Salmo : — 



"A double or zigzag series of teeth along shaft of vomer, 

 sometimes deciduous in the adult." 



It is interesting to note in passing that from a study of their skeletons, 

 and in particular their skulls, Mr. Regan finds that no doubt is left that 

 the Pacific species of salmon and trout " form a perfectly natural group 

 that differs in several characters from the Salmon and Trout of the 

 Atlantic." 



In restricting himself in his book, however, to the British members 

 of the family Salmonidcs, Mr. Regan again distinguishes four, but a 

 different four, genera, namely: (i) Salmo (Salmon and Trout), (2) 

 Salvelinus (Char), (3) Coregonus (Whitefish), and (4) Thymallus 

 (Grayling), a fact which reminds one of the morphologist's caution in 

 viewing systems of classification, and the special features of Salmo and 

 Salvelinus are given thus : — 



" Mouth rather large, the maxillary extending at least to below 



the middle of the eye ; teeth well developed ; scales small or 



moderate; dorsal fin with 10 to 16 rays"; 

 and particularly those of the genus Salmo : — 



" No depression behind the head of the vomer, and a double 



or zigzag series of teeth present on the shaft of that bone, at least 



in the young." 

 It only remains to complete this classification by noting that the genus 

 Salmo embraces two species, and two species only, namely, (i) Salmo 

 salar, which is, of course, the salmon; and (2) Salmo trutia, which is the 

 trout — be that what it may, sea-trout or trout, one or other, or both. 

 Thus we arrive at the basis of the theory that there is only one species 

 of trout in these islands. 



Except in so far as many, up to this point, may, like myself, have 

 been treading on somewhat unfamiliar ground, I see no room for 

 criticism, and we have certainly arrived at a bare systematic conception, 

 if not of the fish itself, at least of the limits within which further 

 particulars may be sought for, and these we may now proceed to seek. 



