1 20 PINNOTHERID.E. 



the crust of the former is as hard as in other brachyurous 

 forms ; but the female is comparatively very large, almost 

 globular, and remarkably soft ; the latter character being 

 doubtless the cause of its requiring the efficient protection 

 of the shells of Mollusca. In other allied forms a some- 

 what analogous habit is observed ; the soft body of Ela- 

 tnene and Hymenosoma demanding extrinsic protection, 

 which they obtain by appropriating to themselves small 

 single shells of dead acephalous Mollusca, as I have my- 

 self seen in several instances, a fact which affords a col- 

 lateral argument in favour of Milne Edwards' 1 s association 

 of these different genera in one family. 



The species of the present genus even yet require careful 

 revision ; and I have found it necessary to comprehend the 

 whole of Dr. Leach's six species in two, which, how- 

 ever, I have not done without the most deliberate con- 

 sideration. 



