]
The _Mollusca_ of the Miocene period are very numerous, but call
for little special comment. Upon the whole, they are generically
very similar to the Shell-fish of the present day; whilst, as
before stated, from fifteen to thirty per cent of the _species_
are identical with those now in existence. So far as the European
area is concerned, the Molluscs indicate a decidedly hotter climate
than the present one, though they have not such a distinctly
tropical character as is the case with the Eocene shells. Thus we
meet with many Cones, Volutes, Cowries, Olive-shells, Fig-shells,
and the like, which are decidedly indicative of a high temperature
of the sea. _Polyzoans_ are abundant, and often attain considerable
dimensions; whilst _Brachiopods_, on the other hand, are few in
number. Bivalves and _Univalves_ are extremely plentiful; and
we meet here with the shells of Winged-Snails (_Pteropods_),
belonging to such existing genera as _Hyalea_ (fig. 239) and
_Cleodora_. Lastly, the _Cephalopods_ are represented both by
the chambered shells of _Nautili_ and by the internal skeletons
of Cuttle-fishes (_Spirulirostra_.)
[Illustration: Fig. 239.--Different views of the shell of _Hyalea
Orbignyana_, a Miocene Pteropod.]
The _Fishes_ of the Miocene Period are very abundant but of little
special importance. Besides the remains of Bony Fishes, we meet
in the marine deposits of this age with numerous pointed teeth
belonging to different kinds of Sharks.
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