. Fishes. Fishes. 268 Isospondyli orbitosphenoid, have been lately transferred to the Haplomi by Boulenger. This arrangement is probably a step in advance. Ganoid traits are present in certain families of Isospondyli. Among these are the gular plate (found in Amia and the Elopida:), doubtless derived from the similar structure in earlier Ganoids; additional valves in the arterial bulb in the cellular air-bladder of Notopterus and Osteoglossum, the spiral intestinal valve in Chirocentridce, and the ganoid scales of the extinct Lepto- lepid(E. The Clupeoidea.—The Isospondyli are divisible into n
. Fishes. Fishes. 268 Isospondyli orbitosphenoid, have been lately transferred to the Haplomi by Boulenger. This arrangement is probably a step in advance. Ganoid traits are present in certain families of Isospondyli. Among these are the gular plate (found in Amia and the Elopida:), doubtless derived from the similar structure in earlier Ganoids; additional valves in the arterial bulb in the cellular air-bladder of Notopterus and Osteoglossum, the spiral intestinal valve in Chirocentridce, and the ganoid scales of the extinct Lepto- lepid(E. The Clupeoidea.—The Isospondyli are divisible into numerous families, which may be grouped roughly under three subdivisions, Clupeoidea, the herring-like forms; the Salmonoidea, the trout-like forms; and the Iiiionii, or lantern-fishes, and their allies. The last-named group should probably be removed from the order of Isospondyli. In the Clupeoidea, the allies of the great family of the herring, the shoulder-girdle is normally developed, retain- ing the mesocoracoid arch on its inner edge, and through the post-temporal is articulated above with the cranium. The fishes in this group lack the adipose fin which is characteristic of most of the higher or salmon-like families. The Leptolepidae.—Most primitive of the Isospondyli is the extinct family of Leptolepidcc, closely aUied to the Ganoid families of PholidophoridcD and Oligoplenridcc. It is composed of Fig. WQ.—Lept lepis dubius Blainville, Lithographic Stone. (After Woodward.) herring-like fishes, with the bones of the head thin but covered with enamel, and the scales thin but firm and enameled on their free portion. There are no fulcra and there is no lateral line. The vertebrae are well developed, but always pierced by the notochord. The genera are Lycoptera, Leptolepis, .Ethalion, and Thrissops. In Lycoptera of the Jurassic of China the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readabili
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