Fig. 47.—A day's catch of Fossil fishes, Phareodus, Diplomystus, etc. Green River Eocene Shales, Fossil, Wyoming. (Photograph by Prof. Wilbur C. Knight.)
The Pantodontidæ.—The bony casque of Osteoglossum is found again in the Pantodontidæ, consisting of one species, Pantodon buchholzi, a small fish of the brooks of West Africa. As in the Osteoglossidæ and in the Siluridæ, the subopercle is wanting in Pantodon.
Fig. 48.—Alepocephalus agassizii Goode & Bean. Gulf Stream.
The Alepocephalidæ are deep-sea herring-like fishes very soft in texture and black in color, taken in the oceanic abysses. Some species may be found in almost all seas below the depth of half a mile. Alepocephalus rostratus of the Mediterranean has been long known, but most of the other genera, Talismania, Mitchillina, Conocara, etc., are of very recent discovery, having been brought to the surface by the deep-sea dredging of the Challenger, the Albatross, the Blake, the Travailleur, the Talisman, the Investigator, the Hirondelle, and the Violante.
CHAPTER IV
SALMONIDÆ
The Salmon Family.—The series or suborder Salmonoidea, or allies of the salmon and trout, are characterized as a whole by the presence of the adipose fin, a structure also retained in Characins and catfishes, which have no evident affinity with the trout, and in the lantern-fishes, lizard-fishes, and trout-perches, in which the affinity is very remote. Probably these groups all have a common descent from some primitive fish having an adipose fin, or at least a fleshy fold on the back.
Of all the families of fishes, the one most interesting from almost every point of view is that of the Salmonidæ, the salmon family. As now restricted, it is not one of the largest families, as it comprises less than a hundred species; but in beauty, activity, gaminess, quality as food, and even in size of individuals, different members of the group stand easily with the first among fishes. The following are the chief external characteristics which are common to the members of the family: