Thus we know that the Belemnites were in
many respects comparable with the existing Calamaries or Squids,
the body being furnished with lateral fins, and the head carrying
a circle of ten "arms," two of which were longer than the others
(fig. 173, A). The suckers on the arms were provided, further,
with horny hooks; there was a large ink-sac; and the mouth was
armed with horny mandibles resembling in shape the beak of a
parrot.
[Illustration: Fig. 173.--A, Restoration of the animal of the
Belemnite; B, Diagram showing the complete skeleton of a Belemnite,
consisting of the chambered phragmacone (a), the guard (b), and
the horny pen (c); C, Specimen of _Belemnites canaliculatus_,
from the Inferior Oolite. (After Phillips.)]
[Illustration: Fig. 174.--_Tetragonolepis (restored), and scales
of the same. Lias.]
Coming next to the _Vertebrates_, we find that the Jurassic _Fishes_
are still represented by _Ganoids_ and _Placoids_. The Ganoids,
however, unlike the old forms, now for the most part possess
nearly or quite symmetrical ("homocercal") tails. A characteristic
genus is _Tetragonolepis_ (fig. 174), with its deep compressed
body, its rhomboidal, closely-fitting scales, and its single
long dorsal fin. Amongst the _Placoids_ the teeth of true Sharks
(_Notidanus_) occur for the first time; but by far the greater
number of remains referable to this group are still the fin-spines
and teeth of "Cestracionts," resembling the living Port-Jackson
Shark.
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