i88 HISTORICAL PALEONTOLOGY. 



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 

 Palaeozoic in their range. The old genera Strophomena, Orthis 

 (fig. 127, c~), Athyris (fig. 127, e), Rhynchonella (fig. 127, g), and 

 Spirifera (fig. 127, /?), 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 Car- 

 boniferous Brachiopods, however, belong to the family of the 

 Productida, 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, /). 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 Producta 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 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 Producta, 

 unlike the ordinary Lamp-shells, lived an independent exist- 

 ence, 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 



