CLADOSELACHE . 79 
ously been structurally known was that of the aberrant 
and highly specialized Acanthodian of the Coal Measures. 
Cladoselache is the most primitive, as well as the oldest, 
of these ancient sharks. It is relatively of small size, 
varying in the length of its species from two to six feet. 
Its outward form, as restored by the writer, is seen in Fig. 
86, and in ventral view in Fig. 86 A. The shape is clearly 
Fig. 86.— Cladoselache fyleri, Newb. X }. Restoration by writer. After speci- 
men in the museum of Columbia College from Cleveland shales, Ohio. 
Fig. 86 A. — Cladoselache fyleri ; ventral aspect. 
that of a modern shark; the fins, too, in their size and 
position, have somewhat of a modern look; and at the 
base of the tail occurs the small horizontal keel of many 
living forms. But in spite of these peculiarities, Cladose- 
lache must be looked upon as the most archaic, and, in 
many ways, the most generalized of known sharks; its 
paired fins are but the remnants of the lateral fold (p. 43), 
serving alone as balancers; the tail, curiously specialized, 
is widely heterocercal, its hinder web lacking supports in 
the upper lobe (p. 36); the vertebral axis is notochordal ; 
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