halus_, and the persistent, genus _Pleurotomaria_; whilst
the free-swimming Univalves (_Heteropoda_)are represented by
_Bellerophon_ and _Porcellia_, and the _Pteropoda_ by the old
genus _Conularia_. With regard to the Carboniferous Univalves,
it is also of interest to note here the first appearance of true
air-breathing or terrestrial Molluscs, as discovered by Dawson
and Bradley in the Coal-measures of Nova Scotia and Illinois. Some
of these (_Conulus priscus_) are true Land-snails, resembling the
existing _Zonites_; whilst others (_Pupa vetusta_, fig. 128) appear
to be generically inseparable from the "Chrysalis-shells" (_Pupa_)
of the present day. All the known forms--three in number--are of
small size, and appear to have been local in their distribution
or in their preservation. More important, however, than any of
the preceding, are the _Cephalopoda_, represented, as before,
exclusively by the chambered shells of the Tetrabranchiates.
The older and simpler type of these, with simple plain septa,
and mostly a central siphuncle, is represented by the straight
conical shells of the ancient genus Orthoceras, and the bow-shaped
shells of the equally ancient _Cyrtoceras_--some of the former
attaining a great size. The spirally-curved discoidal shells
of the persistent genus _Nautilus_ are also not unknown, and
some of these likewise exhibit very considerable dimensions.
Lastly, the more complex family of the _Ammonitidoe_, with lobed
or angulated septa, and a dorsally-placed siphuncle (situated on
the convex side of the curved shells), now for the first time
commences to acquire a considerable prominence. The principal
representative of this group is the genus _Goniatites_ (fig.
129), which commenced its existence in the Upper Silurian, is well
represented in the Devonian, and attains its maximum here. In this
genus, the shell is spirally curved, the septa are strongly lobed
or angulated, though not elaborately frilled as in the Ammonites,
and the siphuncle is dorsal. In addition to _Goniatites_, the
shells of true _Ammonites_, so characteristic of the Secondary
period, have been described by Dr Waagen as occurring in the
Carboniferous rocks of India.

[Illustration: Fig. 129.--_Goniatites (Aganides) Fossoe_.
Carboniferous Limestone.]

[Illustration: Fig. 130.--_Amblypterus macropterus_. Carboniferous.]

Coming finally to the _Vertebrata_, we have in the first place
to very briefly consider the Carboniferous _fishe