184 HISTORICAL PALZONTOLOGY. 
netted fronds of Fenestella, Retepora, and Polypora (fig. 126, @) 
are highly characteristic, as are the slender toothed branches 
of Glauconome (fig. 126, 6). A more singular form, however, is 
the curious Archimedes (fig. 126, c), which is so characteristic 
of the Carboniferous formation of North America. In this re- 
markable type, the colony consists of a succession of funnel- 
shaped fronds, essentially similar to Feveste//a in their structure, 
springing in a continuous spiral from a strong screw-like vertical 
axis. The outside of the fronds is simply striated; but the 
branches exhibit on the interior the mouths of the little cells 
in which the semi-independent beings composing the colony 
originally lived. 
The Brachiopods are extremely abundant, and for the most 
part belong to types which are exclusively or principally 
Paleozoic in their range. The old genera Stvophomena, Orthis 
(fig. 127, ¢), Athyris (fig. 127, e), Rhynchonella (fig. 127, g), and 
Spirifera (fig. 127, 2), 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 Zerebratula (fig. 127, @), 
which underwent a great expansion during later periods, and 
still exists at the present day. The most characteristic Car- 
boniferous Brachiopods, however, belong to the family of the 
Productide, of which the principal genus is Producta itself. 
This family commenced its existence in the Upper Silurian 
with the genus Chonefes, 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 Palaeozoic 
period. The Producte of the Carboniferous are not only ex- 
ceedingly 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 2) 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 
pr oducta”), 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- 
