a distribution little if at all less wide. [Illustration: Fig. 128.--_Pupa (Dendropupa) vetusta_, a Carboniferous Land-snail from the Coal-measures of Nova Scotia. a, The shell, of the natural size; b, The same, magnified; c, Apex of the shell, enlarged; d, Portion of the surface, enlarged. (After Dawson.)] The higher _Mollusca_ are abundantly represented in the Carboniferous rocks by Bivalves (_Lamellibranchs_), Univalves (_Gasteropoda_), Winged-snails (_Pteropoda_), and _Cephalopods_. Amongst the Bivalves we may note the great abundance of Scallops (_Aviculopecten_ and other allied forms), together with numerous other types--some of ancient origin, others represented here for the first time. Amongst the Gasteropods, we find the characteristically Palæozoic genera _Macrocheilus_ and _Loxonema_, the almost exclusively Palæozoic _Euomphalus_, 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