Other species are _Phareodus acutus_, known from the jaws; _P. encaustus_ is known from a mass of thick scales with reticulate or mosaic-like surface, much as in _Osteoglossum_, and _P. æquipennis_ from a small example, perhaps immature. _Phareodus testis_ is frequently found well preserved in the shales at Fossil Station, to the northwestward of Green River. Whether all these species possess the peculiar structure of the scales, and whether all belong to one genus, is uncertain. [Illustration: FIG. 45.—_Phareodus testis_ (Cope). From a specimen 20 inches long collected at Fossil, Wyo., in the Museum of the Univ. of Wyoming. (Photograph by Prof. Wilbur C. Knight.) ] In Eocene shales of England occurs _Brychætus muelleri_, a species closely related to _Phareodus_, but the scales smaller and without the characteristic reticulate or mosaic structure seen in _Phareodus encaustus_. [Illustration: FIG. 46.—Deposits of Green River Shales, bearing _Phareodus_, at Fossil, Wyoming. (Photograph by Wilbur C. Knight.) ] [Illustration: 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_. [Illustration: 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.