110 
THE GEOLOGIST. 
Since the Brachiopoda have become the object of scientific and con- 
scientious study, it has always been believed that the Productidce and 
Strophomenidce were provided with oral arms, although little positive 
evidence as to their presence has been more often left in the interior 
of the valves. In many species of Strophomenidm and Productidce the 
space left for the animal between the valves is so exceedingly small 
that one can hardly conceive how all the parts could have been lodged 
or disposed ; still they did exist, and, no doubt, fulfilled the same 
functions, and were as perfectly organized as in those species which 
possessed a more spacious dwelling; just as one of those very thin 
Geneva watches of modern times is as perfect in its parts and action, 
as were the far more bulky time-pieces manufactured by our ancestors. 
In all the species of existing articulated genera in which the animal 
has been examined, the oral arms were attached or supported by cal- 
careous processes in connexion with the dorsal valves, so that it 
behoves us to seek for any probable attachment in that valve also 
among the Productidce and StropliomcnidcB. Mr. S. P. Woodward, 
who has devoted much attention, in conjunction with myself, to the 
internal character of the Productidce, has supposed that the arms were 
perhaps attached to those two testaceous prominences (PI. III. fig. 2, w, 
and PI. IV. fig. 5, w), which are visible in some species of Producta and 
Aulosteges, a little lower down than the occlusor muscular impressions. 
These prominences may possibly have given support to the mouth 
somewhat in the manner of the crural processes of other species, and 
thus they may be said to have sustained also the bases of the arms. 
This suggestion, however, cannot be demonstrated by the direct 
examination or comparison of the animals of existing species of other 
families. These prominences are not present in Strophalosia or 
Chonetes, and therefore are not common to the group. 
In the Museum of Practical Geology I found a very remarkable 
specimen of Producta gigantea, which, although imperfect at the 
margin and cardinal process, possessed all the important parts relating 
to the interior of both valves as perfectly preserved as could be 
desired. From this, the two large representations accompanying this 
paper (PI. III. figs. 1 and 2) have been carefully drawn. It will be 
observed that in the interior of the dorsal valve there exist two much 
larger conical projections (z), situated immediately under the emi- 
