494 TUBE-BLADDERED GROUP. 



excellent quality of their flesh, which in many forms is of a more or less strongly 



marked pinkish hue, brought about by the crustaceans on which these carnivorous 



fishes so largely feed. Fossil marine salmonoids, some of which belong to existing 



genera, are known from the upper Cretaceous period, several of them apparently 



connecting the family very closely with the herrings. As mentioned above (p. 487) 



the more typical members of the family have the parietal bones of the skull 



separated from one another by the supraoccipital, but in Coregonus and Thymallus 



they unite together in front of it. There is, however, a genus (Stenodus) in 



which both conditions exist, so that there is no justification for making the 



union of the parietals a reason for referring Coregonus to a family apart. In all 



cases the supraoccipital extends forwards to join the frontals (passing beneath 



the parietals in the genera where those unite), and is thus quite different from the 



condition obtaining in the carps and characinoids. 



Having the dorsal nearly or quite opposite the pelvic fins, the 

 Typical Group. f . a • 



members of the typical genus Salmo are characterised by the small 



size of the scales of the body, the strong and fully developed teeth, and the presence 

 of not more than fourteen raj's in the anal fin, and of numerous blind appendages 

 to the intestine. The cleft of the mouth is always deep, the maxilla extending up to 

 or beyond the line of the eye. Conical teeth are present not only in the margins 

 of the jaws, but likewise on the vomer and palatine bones, as well as on the tongue, 

 although there are none on the pterygoids. The eggs are remarkable for their 

 relatively large size ; and the young, like those of most or all the other genera, are 

 marked with dark crossbars. In the males the lower jaw is more developed than in 

 the females, and at certain seasons may be developed into an upturned hook. The 

 genus is confined to the colder portions of the Northern Hemisphere, its southern 

 limits in the Old World being the rivers of the Hindu Kush and the Atlas range, 

 and in America the rivers flowing into the head of the Gulf of California. 



Few zoological subjects have given rise to a greater amount of discussion than 

 the life-history of the members of this genns, and the number of species by which 

 it is represented. As regards the latter point, great difference of opinion still 

 prevails among experts. Thus, for instance, Day considered that all the 

 indigenous British salmonoids might be arranged under three specific t}~pes, 

 namely, the salmon, the trout, and the charr ; while other authorities admit an 

 almost endless amount of species. The subject is not one which admits of dis- 

 cussion in this work ; and we shall accordingly confine our notice to the salmon, the 

 typical sea- and river-trout, and the charr. As regards the variability of these 

 fishes we may, however, quote a passage from Dr. Gunther, who writes that " these 

 are dependent on age, sex, and sexual development, food, and the properties of the 

 water. Some of the species interbreed, and the hybrids mix again with one of the 

 parent species, thus producing an offspring more or less similar to the pure breed. 

 The coloration is, first of all, subject to variation; and consequently this character 

 but rarely assists in distinguishing a species, there being not one which would show 

 in all stages of development the same kind of coloration. The 3'oung of all the 

 species are barred ; and this is so constantly the case that it may be used as a 

 generic, or even as a family character, not being peculiar to $<t?)u<> alone, but also 

 common to Thymallus, and probably to Coregonus. The number of liars is not 



