The _Brachiopods_ are extremely abundant, and for the most part belong to types which are exclusively or principally Palæozoic in their range. The old genera _Strophomena, Orthis_ (fig. 127, c), _Athyris_ (fig. 127, e), _Rhynchonella_ (fig. 127, g), and _Spirifera_ (fig. 127, h), are still well represented--the latter, in particular, existing under numerous specific forms, conspicuous by their abundance and sometimes by their size. Along with these ancient groups, we have representatives--for the first time in any plenty--of the great genus _Terebratula_ (fig. 127, d), which underwent a great expansion during later periods, and still exists at the present day. The most characteristic Carboniferous Brachiopods, however, belong to the family of the _Productidoe_, of which the principal genus is _Producta_ itself. This family commenced its existence in the Upper Silurian with the genus _Chonetes_, distinguished by its spinose hinge-margin. This genus lived through the Devonian, and flourished in the Carboniferous (fig. 127, f). The genus _Producta_ itself, represented in the Devonian by the nearly allied _Productella_, appeared first in the Carboniferous, at any rate, in force, and survived into the Permian; but no member of this extensive family has yet been shown to have over-lived the Palæozoic period. The _Productoe_ of the Carboniferous 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