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THE GEOLOGIST. 



Since the Brachiopoda have become the object of scientific and con- 

 scientious study, it has always been believed that the Prodiictidce and 

 StrophomenidcB 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 Strophomenidoe and Productidoe 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 Strophomenidce. 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 PL IV. fig. 5, iv\ 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 

 Ckonetes, 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- 



