Isospondyli 269 
vertebral centra are feebly developed, and the dorsal fin short 
and posterior. In Leptolepis the anal is short and placed ~ 
behind the dorsal. There are many species, mostly from the 
Triassic and lithographic shales of Europe, one being found 
in the Cretaceous. Leptolepis coryphenoides and Leptolepis 
dubius are among the more common species. Azthalion (knorrt) 
differs in the form of the jaws. In Thrissops the anal fin is 
long and opposite the dorsal. Thrissops salmonea is found 
in the lithographic stone; Thrissops exigua in the Cretaceous. 
In all these early forms there is a hard casque over the brain- 
cavity, as in the living types, Ama and Osteoglossum. 
The Elopide.—The family of Elopide contains large fishes 
herring-like in form and structure, but having a flat membrane- 
Fig. 200.—Ten-pounder, Elops saurus L. An ally of the earliest bony fishes. 
Virginia. 
bone or gular plate between the branches of the lower jaw, as 
in the Ganoid genus Amia. The living species are few, abound- 
ing in the tropical seas, important for their size and numbers, 
Fic. 201.—A primitive Herring-like fish, Holcolepis lewesiensis, Mantell, restored. 
Family Elopide. English Chalk. (After Woodward.) 
though not valued as food-fishes save to those who, like the 
Hawaiians and Japanese, eat fishes raw. These people prefer 
