86 PHYSOSTOMI. 



time that S. alius began to be suppressed under tbe belief that it was the young 

 or a variety of the salmon- or sea-tront. Jenyns observed that neither he nor 

 Tarrell could see any appreciable difference between them. It is abundantly 

 evident, however, that Yarrell in his Salmo trutta includes the sewin of the south, 

 Wales, and Ireland, as well as the phinock or hirling of Scotland, which he 

 observes is the S. albus, but that he could not distinguish it from his 8. trutta. 

 Agassiz looked upon these forms as one, so did also Parnell, White, and Thompson. 

 Dr. Giinther reverted to the views of Pennant, remarking how the species in his 

 opinion differed from S. trutta, five out of seven of his types being from Tarrell's 

 and Parnell's collections. But he placed all the synonyms of 8. albus under the 

 head of 8. trutta, even when the authors had referred to both as species. It thus 

 came to pass that this northern species, or 8. albus, has since 1866 been known as 

 8. brachypoma, Giinther, which is the more remarkable, as prior to the publication 

 of the volume of the Catalogue in which it was first thus named, the author was 

 able to record in the Addenda, p. 357, that he had received examples from the 

 Beauly, " and that they are named there ' Phinok.' " 



Although a chain of examples, passing from this form into the river trout, 

 has not been recognized, I shall, when describing the short-headed fresh water 

 Loch Leven trout, give my reasons for supposing that it is most probably a 

 descendant of this short-headed marine variety, and also show how it does not 

 appear improbable that it, under certain conditions, may pass into and be lost in 

 the Salmo fario. These numerous deviations from the type tend to demonstrate 

 the adaptability of the species to varying conditions of life, and as we do not 

 perceive such in the salmon, one would expect to find the trout in one or other 

 of its forms extending further, or accommodating itself to greater ranges of the 

 globe, and this is exactly what we observe in nature. 



Variety I. — Salmo cambricus, Plate CXII, fig. 1 . 



Salmulus, Willughby (young'). The grey salmon, part, Pennant, Brit. Zool. 

 (Ed. 1776) iii, p. 295, and (Ed. 1812) iii, p. 394. Salmo, no. 2, Artedi, Genera, 

 p. 12, Synon, p. 23, Spe. 50 ; Linn. Fauna Suec. p. 116, no. 307. 



Salmo canibrims, Donovan, Brit. Pishes, iv, pi. xci ; Richards. Faun. Bor. 

 Amer. Fish. p. 141, pi. xci, fig. 2 ; Giinther, Catal. vi, p. 34 ; Houghton, Brit. 

 F. W. Fishes, p. 99, c. fig. 



Sewen and Blue poll, Couch, Fish. Brit. Isles, iv, pp. 208, 219, pis. ccxiii, ccxvi. 



Salmo eriox, Gmel. Linn. p. 1366; Bon. Ency. Ich. p. 159; Turton, Brit. 

 Fauna, p. 103 ; Flem. Brit. An. p. 180 ; Jenyns, Manual, p. 422 ; Yarrell, Brit. 

 Fish. (ed. 1) ii, p. 31, c. fig. (ed. 2) ii, p. 71 (ed. 3) i, p. 231 ; Kroyer, Dan. 

 Fiske, ii, p. 602 ; Thompson, Proc. Zool. Soc. 1837, p. 57, and Nat. Hist. Ireland, 

 iv, p. 148 ; Nilss. Skan. Fauna, p. 395 ; White, Catal. p. 7& (part). 



The sewin of the south coast, Wales, and Ireland, similarly to the salmon-trout 

 of the east coast of Scotland, has both a long- and a short-headed variety.* 

 Two examples of sewin from fiosshire, presented by Mr. Godman, are in the 

 British Museum. So similar, however, is this fish externally to the salmon-trout, 

 and passes into it so exactly, that of one of Yarrell's examples in the national 

 collection being a skin destitute of any record of its ooecal appendages. 

 Dr. Giinther has remarked that "it is one of those specimens in which the 

 distinctive characters of the species are very little developed : and it is quite 

 possible that the specimen came from Scotland, and belongs to Salmo trutta." 

 Having thus shown how difficult, if not impossible, it may be to discriminate 

 between these two forms, I will pass on to how physical causes may occasion 

 changes, so that it has become very uncertain which of the two that is 

 under examination, and for this purpose I must again revert to the Tas- 

 manian experiment. Anadromous salmon ova were collected in this country, 

 and transmitted to the Antipodes, where they arrived in May, 1866. Some 



* In Plate CXX of Salmo fontinalis the great difference occasioned through physical causes in 

 the comparative length of the head in a saUnonoid fish is shown. 



