THE’ JURASSIC PERIOD: 241 
fishes are still represented by Ganoids and Placoids. The 
Ganoids, however, unlike the old forms. now for the most 
Fig. 173.—A, Restoration of the animal of the Belemnite ; B, Diagram showing the 
complete skeleton of a Belemnite, consisting of the chambered phragmacone (qa), the 
enard (6), and the horny pen (c); C, Specimen of Belemnites canaliculatus, from the 
Inferior Oolite. (After Phillips.) 
part possess nearly or quite symmetrical (“‘ homocercal ”) tails. 
A characteristic genus is Zetragonolepis (fig. 174), with its 
wy e, 
SEAS EE NTS ERNE 2 
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Fig. 174.—Tetragonolepis (restored), and scales of the same. Lias. 
deep, compressed body, its rhomboidal, closely-fitting scales, 
and its single long dorsal fin. Amongst the Placoids the teeth 
Q 
