rous are not only exceedingly abundant,
but they have in many instances a most extensive geographical range,
and some species attain what may fairly be considered-gigantic
dimensions. The shell (fig. 127, a and b) is generally more
or less semicircular, with a straight hinge-margin, and having
its lateral angles produced into larger or smaller ears (hence
its generic name--"_cochlea producta_"). One valve (the ventral)
is usually strongly convex, whilst the other (the dorsal) is flat
or concave, the surface of both being adorned with radiating
ribs, and with hollow tubular spines, often of great length.
The valves are not locked together by teeth, and there is no
sign in the fully-grown shell of an opening in or between the
valves for the emission of a muscular stalk for the attachment
of the shell to foreign objects. It is probable, therefore, that
the _Productoe_, unlike the ordinary Lamp-shells, lived an
independent existence, their long spines apparently serving to
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
_Euomp