Isospondyli re) 
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. primevus, is found in the same region. 
The Clupeide.—The great herring family, or Clupeide, 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 tftee pieces. In most of the genera the belly ends in a 
serrated edge, though in the true herring this is not very evident, 
Fie. 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 pallast, 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 vertebree 
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) vertebra. 
The alewife, or branch-herring (Pomolobus pseudoharengus), 
ascends the rivers to spawn and has become land-locked in 
1I—4 
