nged-snails," or _Pteropods_, we find new forms
of the old genera _Tentaculites_ and _Conularia_ (fig. 100).
The latter, with its fragile, conical, and often beautifully
ornamented shell, is especially noticeable.

[Illustration: Fig. 100.--_Conularia ornata, of the natural size.
Devonian, Europe.]

[Illustration: Fig. 101.--_Clymenia Sedgwickii_. Devonian, Europe.]

The remains of _Cephalopoda_ are far from uncommon in the Devonian
deposits, all the known forms being still Tetrabranchiate. Besides
the ancient types _Orthoceras_ and _Cyrtoceras_, we have now
a predominance of the spirally-coiled chambered shells of
_Goniatites_ and _Clymenia_. In the former of these the shell is
shaped like that of the _Nautilus_; but the partitions between the
chambers ("septa") are more or less lobed, folded, or angulated,
and the "siphuncle" runs along the _back_ or convex side of the
shell--these being characters which approximate _Goniatites_ to
the true Ammonites of the later rocks. In _Clymenia_, on the
other hand, whilst the shell (fig. 101) is coiled into a flat
spiral, and the partitions or septa are simple or only slightly
lobed, there is still this difference, as compared with the
_Nautilus_, that the tube of the siphuncle is placed on the _inner_
or concave side of the shell. The species of _Clymenia_ are
exclusively Devonian in their range; and some of the limestones
of this period in Germany are so richly charged with fossils of
this genus as to have received the name of "Clymenien-kalk."

The sub-kingdom of the _Vertebrates_ is still represented by
_Fishes_ only; but these are so abundant, and belong to such
varied types, that the Devonian period has been appropriately
called the "Age of Fishes." Amongst the existing fishes there are
three great groups which are of special geological importance,
as being more or less extensively represented in past time. These
groups are: (1) The _Bony Fishes_ (_Teleostei_), comprising most
existing fishes, in which the skeleton is more or less completely
converted into bone; the tail is symmetrically lobed or divided
into equal moieties; and the scales are usually thin, horny,
flexible plates, which overlap one another to a greater or less
extent. (2) The _Ganoid Fishes_ (_Ganoidei_), comprising the modern
Gar-pikes, Sturgeons, &c., in which the skeleton usually more or
less completely retains its primitive soft and cartilaginous
condition; the tail is generally markedly unsymmetr