e total extinction
of the great family of the "Belemnites." No form referable to
this group has hitherto been found in any Tertiary stratum; but
the internal skeletons of Cuttle-fishes (such as _Belosepia_)
are not unknown.

[Illustration: Fig. 220.--_Limnoea pyramidalis_. Eocene.]

[Illustration: Fig. 221.--_Physa columnaris_. Eocene.]

[Illustration: Fig. 222.--_Cyclostoma Arnoudii_. Eocene.]

Remains of _Fishes_ are very abundant in strata of Eocene age,
especially in certain localities. The most famous depot for the
fossil fishes of this period is the limestone of Monte Bolca,
near Verona, which is interstratified with beds of volcanic ashes,
the whole being referable to the Middle Eocene. The fishes here
seem to have been suddenly destroyed by a volcanic eruption,
and are found in vast numbers. Agassiz has described over one
hundred and thirty species of Fishes from this locality, belonging
to seventy-seven genera. All the _species_ are extinct; but about
one-half of the _genera_ are represented by living forms. The
great majority of the Eocene Fishes belong to the order of the
"Bony Fishes" (_Teleosteans_), so that in the main the forms
of Fishes characterising the Eocene are similar to those which
predominate in existing seas. In addition to the above, a few
_Ganoids_ and a large number of _Placoids_ are known to occur
in the Eocene rocks. Amongst the latter are found numerous teeth
of true Sharks, such as _Otodus_ (fig. 224) and _Carcharodon_.
The pointed and serrated teeth of the latter sometimes attain
a length of over half a foot, indicating that these predaceous
fishes attained gigantic dimensions; and it is interesting to
note that teeth, in external appearance very similar to those
of the early Tertiary genus _Carcharodon_, have been dredged
from great depths during the recent expedition of the Challenger.
There also occur not uncommonly the flattened teeth of Rays (fig.
225), consisting of flat bony pieces placed close together, and
forming "a kind of mosaic pavement on both the upper and lower
jaws" (Owen).

[Illustration: Fig. 223.--_Rhombus minimus_, a small fossil Turbot
from the Eocene Tertiary, Monte Bolca.]

[Illustration: Fig. 224.--Tooth of _Otodus obliquus_. Eocene.]

[Illustration: Fig. 225.--Flattened dental plates of a Ray
(_Myliobatis Edwardsii_). Eocene.]

In the class of the _Reptiles_, the disappearance of the
characteristic Mesozoic types is as marked a phenomenon as the
int