4664 Fishes. 



And now, in respect of their distinguishing or specific characters, 

 external and internal: they are a red-spotted trout, both above and 

 below the lateral line ; their head and fins are proportionally more 

 delicate than those of the common red-spotted trout of the Scottish 

 rivers and brooks ; their proportions are, in fact, somewhat inter- 

 mediate between the delicate lacustrine trout (Salmo Levensis) and 

 the common riverine species, neither do I believe them transmutable 

 or convertible into any other species of trout by any natural changes 

 now in operation. What forms they might assume if compelled to 

 live wholly in the sea, or in waters (whether lacustrine or riverine) 

 wholly fresh, is a question I shall not discuss here ; my own opinion is 

 that they would become extinct. 



The place it is entitled to in the scale of the natural family of 

 the Salmonidae I shall consider presently. The teeth are nearly as 

 large again as in the common river trout, and the dentition is as 

 follows : — 



Upper jaw. — Supermaxillary 25 -f- 25 = 50 



Intermaxillary 10 + 10 = 20 



Palatine 14 + 14 = 28 



Vomerine as usual in a double alter- 

 nating row ..... 20 



Lower jaw or mandible . . . . . . 20 -J- 20 = 40 



Lingual 6 + 6 = 12 



These teeth are reckoned, not from the actual number of teeth present, 

 which varies of course at almost every instant in the life of the fish, 

 but from the number of distinct mucous cavities fitted for the recep- 

 tion of the teeth, whose number determines rigorously that of the teeth 

 which are present or which are in process of development, and which 

 disappear when, by age or maturity, a bone is about to become 

 edentulous. 



The vomerine teeth, the peculiar characteristic of the Salmonidae, 

 and to the arrangement and development of which M. Valenciennes 

 attaches so much importance, do not differ in any remarkable way 

 from others of the trout species. The anterior transverse vomerine 

 teeth are not more distinct than they are in the common and Leven 

 trout; that is, they do not extend beyond the mesial line, as in the 

 common or true salmon. Having neglected to note with sufficient 

 care the dentition of the large or full-grown estuary trout, those of 

 4 lbs. for example, I am unable to say what changes take place in the 

 vomerine teeth. The law of edentulation (loss of teeth), as regards 



