=The Notopteridæ.=—The _Notopteridæ_ is another small family in the rivers of Africa and the East Indies. The body ends in a long and tapering fin, and, as usual in fishes which swim by body undulations, the ventral fins are lost. The belly is doubly serrate. The air-bladder is highly complex in structure, being divided into several compartments and terminating in two horns anteriorly and posteriorly, the anterior horns being in direct communication with the auditory organ. A fossil _Notopterus_, _N. primævus_, is found in the same region. =The Clupeidæ.=—The great herring family, or _Clupeidæ_, comprises fishes with oblong or herring-shaped body, cycloid scales, and feeble dentition. From related families it is separated by the absence of lateral line and the division of the maxillary into three pieces. In most of the genera the belly ends in a serrated edge, though in the true herring this is not very evident, and in some the belly has a blunt edge. Some of the species live in rivers, some ascend from the sea for the purpose of spawning. The majority are confined to the ocean. Among all the genera, the one most abundant in individuals is that of _Clupea_, the herring. Throughout the North Atlantic are immense schools of _Clupea harengus_. In the North Pacific on both shores another herring, _Clupea pallasi_, is equally abundant, and with the same market it would be equally valuable. As salted, dried, or smoked fish the herring is found throughout the civilized world, and its spawning and feeding-grounds have determined the location of cities. [Illustration: FIG. 38.—Herring, _Clupea harengus_ L. New York. ] The genus _Clupea_, of northern distribution, has the vertebræ in increased number (56), and there are weak teeth on the vomer. Several other genera are very closely related, but ranging farther south they have, with other characters, fewer (46 to 50) vertebræ. The alewife, or branch-herring (_Pomolobus pseudoharengus_), ascends the rivers to spawn and has become landlocked in the lakes of New York. The skipjack of the Gulf of Mexico, _Pomolobus chrysochloris_, becomes very fat in the sea. The species becomes landlocked in the Ohio River, where it thrives as to numbers, but remains lean and almost useless as food. The glut-herring, _Pomolobus æstivalis_, and the sprat, _Pomolobus sprattus_, of Europe are related forms. [Illustration: FIG. 39.—Alewife, _Pomolobus pseudoharengus_ (Wilson). Potomac River. ] Very near also to the herring is the shad (_Alosa sapidissima_) of the eastern coasts of America, and its inferior relatives, the shad of the Gulf of Mexico (_Alosa alabamæ_), the Ohio River shad (_Alosa ohiensis_), very lately discovered, the Allice shad (_Alosa alosa_) of Europe, and the Thwaite shad (_Alosa finta_). In the genus _Alosa_ the cheek region is very deep, giving the head a form different from that seen in the herring.