FIG. 32.—Milkfish, _Chanos chanos_ (L.). Mazatlan. ] [Illustration: FIG. 33.—Mooneye, _Hiodon tergisus_ Le Sueur. Ecorse, Mich. ] =The Hiodontidæ.=—The _Hiodontidæ_, or mooneyes, inhabit the rivers of the central portion of the United States and Canada. They are shad-like fishes with brilliantly silvery scales and very strong sharp teeth, those on the tongue especially long. They are very handsome fishes and take the hook with spirit, but the flesh is rather tasteless and full of small bones, much like that of the milkfish. The commonest species is _Hiodon tergisus_. No fossil _Hiodontidæ_ are known. [Illustration: FIG. 34.—_Istieus grandis_ Agassiz. Family _Pterothrissidæ_. (After Zittel.) ] [Illustration: FIG. 35.—_Chirothrix libanicus_ Pictet & Humbert. Cretaceous of Mt. Lebanon. (After Woodward.) ] =The Pterothrissidæ.=—The _Pterothrissidæ_ are sea-fishes like _Albula_, but more slender and with a long dorsal fin. They live in deep or cold waters along the coasts of Japan, where they are known as gisu. The single species is _Pterothrissus gissu_. The fossil genus _Istieus_, from the Upper Cretaceous, probably belongs near the _Pterothrissidæ_. _Istieus grandis_ is the best-known species. Another ancient family, now represented by a single species, is that of the _Chirocentridæ_, of which the living type is _Chirocentrus dorab_, a long, slender, much compressed herring-like fish, with a saw-edge on the belly, found in the East Indies, in which region _Chirocentrus polyodon_ occurs as a fossil. Numerous fossil genera related to _Chirocentrus_ are enumerated by Woodward, most of them to be referred to the related family of _Ichthyodectidæ_ (_Saurodontidæ_). Of these, _Portheus_, _Ichthyodectes_, _Saurocephalus_ (_Saurodon_), and _Gillicus_ are represented by numerous species, some of them fishes of immense size and great voracity. _Portheus molossus_, found in the Cretaceous of Nebraska, is remarkable for its very strong teeth. Species of other genera are represented by numerous species in the Cretaceous of both the Rocky Mountain region and of Europe. [Illustration: FIG. 36.—Gigantic skeleton of _Portheus molossus_ Cope. (Photograph by Charles H. Sternberg.) ] =The Ctenothrissidæ.=—A related family, _Ctenothrissidæ_, is represented solely by extinct Cretaceous species. In this group the body is robust with large scales, ctenoid in _Ctenothrissa_, cycloid in _Aulolepis_. The fins are large, the belly not serrated, and the teeth feeble. _Ctenothrissa vexillifera_ is from Mount Lebanon. Other species occur in the European chalk. In the small family of _Phractolæmidæ_ the interopercle, according to Boulenger, is enormously developed. [Illustration: FIG. 37.—_Ctenothrissa vexillifera_ Pictet, restored. Mt. Lebanon Cretaceous. (After Woodward.) ]