The Ganoids 29 
Jurassic of South Dakota. Pleuropholis, with the scales on the 
lateral line, which runs very low, excessively deepened, is also 
widely distributed. I have before me a new species from the 
Cretaceous rocks near Los Angeles. The Archeomenide differ 
from Pholidophoride in having cycloid scales. In both families 
the vertebree are reduced to rings about the notochord. From 
fishes allied to the Pholidophoride the earliest Isospondyli are 
probably descended. 
In the Aspidorhynchide the snout is more or less produced, 
the mandible has a distinct presymphysial bone, the vertebrze 
are double-concave or ring-like, and the fins are without fulcra. 
This family constitutes the suborder A:theospondyli. In form 
these fishes resemble Albula and other modern types, but have 
Fig. 22.—Pholidophorus crenulatus Egerton. Lias. (After Woodward.) 
mailed heads and an ancient type of scales. Two genera are 
well known, Aspidorhynchus and Belonostomus. Aspidorhyn- 
chus acuttrostris reaches a length of three feet, and is found in 
the Triassic lithographic stone of Bavaria. Other species 
occur in rocks of Germany and England. 
Belonostomus has the snout scarcely produced. Belono- 
stomus sphyrenoides is the best known of the numerous species, 
all of the Triassic, Jurassic, and Cretaceous. 
Family Lepisosteidez.—The family of Lepzsosterde, constituting 
the suborder Ginglymodi (yiyyAvmos, hinge), is characterized 
especially by the form of the vertebre. 
These are opisthoccelian, convex in front and concave behind, 
as in reptiles, being connected by ball-and-socket joints. The tail 
is moderately heterocercal, less so than in the Halecomorphi, and 
the body is covered with very hard, diamond-shaped, enameled 
