Isospondyli 41 
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 Isospondylt. 
Among these are the gular plate (found in Amza and the Elopide), 
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 Chirocentride, and the ganoid scales of the extinct Lepto- 
lepide, 
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 Juiomi, or lantern-fishes, and their allies. The 
last-named group should probably be removed from the order of 
Isospondylt1. 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 Leptolepide.—Most primitive of the Isospondyli is the 
extinct family of Leptolepide, closely allied to the Ganoid families 
of Pholidophoride and Oligopleuride. It is composed of graceful, 
Fig. 27.—Leptolepis 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 vertebre are well developed, but always pierced by the 
notochord. The genera are Lycoptera, Leptolepis, A:thalion, 
and Thrissops. In Lycoptera of the Jurassic of China the 
