SALMONOIDEiE. 139 



Being convinced that much assistance in discriminating the different species of 

 trout may be obtained by carefully observing the forms and relative sizes of the 

 various parts of the head, particularly the opercular pieces, the heads of the Ame- 

 rican trouts, described in the following pages, are figured of the natural size, and 

 two plates of the heads of British trouts are added for the purpose of comparison. 

 The proportion of the head to the whole body, the dentition particularly of the 

 vomer and tongue, and the form and size of the scales, have also been carefully 

 noted in the descriptions. I have recently been led to conclude that the number 

 of the pyloric cseca ought to be taken into account as a specific distinction ; but 

 living as I do in a part of the country where there are no trouting streams, and 

 far distant from waters affording a variety of species, I have been unable to carry 

 my anatomical researches to the extent that I could have wished ; and I much 

 regret that I did not turn my attention to this subject when I had it in my power 

 to examine recent American specimens. I have been indebted, it is true, to kind 

 friends for numerous presents of trouts from the Orkneys, Sutherlandshire, Kin- 

 rosshire, Dumfriesshire, and Wales ; but such distant land-carriage was productive, 

 in many cases, of so much injury to the specimens, that I could not always satis- 

 factorily determine how far differences in the number of the cseca were connected 

 with variations of external form. 



The following species of trout are mentioned in the Regne Animal as existing 

 in Europe. Salmo salar, hamatus, Schiefermulleri, hucho, lemanus, trutta, fario, 

 punctatus, marmoratus, sahelinus, alpinus, salmulus (samlet or par), and umbla *. 

 From the want of continental specimens for comparison, I am unable to say, with 

 any pretension to correctness, how many of the British trouts can be arranged under 



* Nilsson enumerates as inhabitants of the waters of Scandinavia, — I. Trutta : — Salmo salar, ocla, trutta, truttula, 

 fario, punctatus. II. Salvelini : — Salmo ventricosus, carbonarius, alpinus, pallidas, salvelinus, and rutilus. M. Agassiz, 

 however, reduces the species on the continent of Europe to six, but admits that he has seen additional ones in Great Bri. 

 tain. His species are : — 



•' 1. Salmo umbla, Linn., the Char of England, the Ombre Chevalier of the Lake of Geneva, the Ratheh of Swiss Ger- 

 many, and the Schwartz rental of Saltzburg. — Synonyms : S. salvelinus, alpinus, Linn., salmarinus (but not the S. 



alpinus of Bloch). This fish is found in England, Ireland, Sweden, Switzerland, and in all the southern parts of 



Germany. 

 " 2. S. fario, Linn. — the Trout of brooks, Common trout, Gillaroo trout, and Par. Synonyms : Salmo silvaticus, 



Schrank, alpinus, Bloch, pmnctaius and marmoratus, Cuvier, and erythrinus, Linn. It is found as extensively as the 



first species. 

 •' 3. S. trutta, Linn. Sea Trout — Salmon Trout. It is the same as the Salmo lemanus of Cuvier, and the S. albatus of 



Rondeletius. It is found as extensively as the two preceding species. 

 " 4. S. lacustris, Linn. The same as the S. illanca and Schiefermulleri of Bloch. It is found in the lakes of Lower 



Austria, and in the Rhine above Constance. 

 •' 5. S, salar, Linn. The true Salmon. The Salmo hamatus of Cuvier is the old fish, and the S. Goedenii of Bloch is the 



young. Found in the northern seas, whence it ascends the rivers even as high as the Swiss lakes. 

 ■■'6. S. hucho, Linn. Peculiar to the waters of the Danube.'' (Agassiz. Paper read before the British Association at 



the Edinburgh meeting, reported in Lit. Gaz.) 



T 2 



