494 
TUBE-BLADDERED GROUP. 
Typical 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 
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 rays 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 genus, 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, Hay considered that all the 
indigenous British salmonoids might be arranged under three specific types, 
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 young 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 Salmo alone, but also 
common to Thymallus , and probably to Coregonus. The number of bars is not 
