The Bivalves (_Lamellibranchiata_) of the Devonian call for no special comment, the genera _Pterinea_ and _Megalodon_ being, perhaps, the most noticeable. The Univalves (_Gasteropods_), also, need not be discussed in detail, though many interesting forms of this group are known. The type most abundantly represented, especially in America, is _Platyceras_ (fig. 99), comprising thin, wide-mouthed shells, probably most nearly allied to the existing "Bonnet-limpets," and sometimes attaining very considerable dimensions. We may also note the continuance of the genus _Euomphalus_, with its discoidal spiral shell. Amongst the _Heteropods_, the survival of _Bellerophon_ is to be recorded; and in the "Winged-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."