Isospondyli 



49 



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 Notop- 

 terus, N. prim&vus, is found in the same region. 



The Clupeidae. The great herring family, or Clupeida, com- 

 prises 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, 



FIG. 38. Herring, Clupea harengus L. New York. 



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 spawn- 

 ing. 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 im- 

 mense 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. 



The genus Clupea, of northern distribution, has the vertebrae 

 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) vertebrae. 

 The alewife, or branch-herring (Pomolobus pseu doharengus) , 

 ascends the rivers to spawn and has become land-locked in 



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