anchor them firmly in the mud or ooze of the sea-bottom; but Mr Robert Etheridge, jun.; has recently shown that in one species the spines were actually employed as organs of adhesion, whereby the shell was permanently attached to some extraneous object, such as the stem of a Crinoid.  The two species here figured are interesting for their extraordinarily extensive geographical range—­Producta semireticulata (fig. 127, a) being found in the Carboniferous rocks of Britain, the continent of Europe, Central Asia, China, India, Australia, Spitzbergen, and North and South America; whilst P.  Longispina (fig. 127, b) has 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 Palaeozoic genera Macrocheilus and Loxonema, the almost exclusively Palaeozoic 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