MOLLUSC A. 



The voyage of H. M. S. Sulphur proved eminently prolific in shells, and a very 

 considerable acquisition has been made to science. The very careful search 

 which was unceasingly made on all the shores visited throughout the voyage, and 

 the constant use of the dredge and trawl, whenever circumstances permitted, 

 have contributed to this ; but, above all, the close examination of the proceeds of 

 the dredge, by siftings and diligent washings, brought into notice a great number 

 of small but very interesting species, the great majority of which was previously 

 unknown. This method of search has been hitherto practised to such a very 

 limited extent, and comparatively in such few places, that it is beyond conjecture 

 the number of species to be brought to light is very great, and will most 

 probably much exceed those already known. Nor will the labours of the concho- 

 logist be rewarded only by small species, for many of no mean size were thus 

 obtained by us, as an inspection of the plates will show. Indeed it is truly sur- 

 prising how fecund is the bed of the ocean, in not only Mollusca but organized 

 beings generally ; and it has often been my fortune to have been suddenly inun- 

 dated by the dredge and trawl with a far greater number of beings than the 

 climate, and conveniences of a vessel, permitted me to preserve, and which also 

 gave me several days of unremitting occupation. Confining our attention to the 

 shells, — for, though less worthy, we avoid some circumlocution by speaking of 

 them instead of the animals, — we on one occasion spent a forenoon in the Bay of 

 Guayaquil in using the dredge, and the result gave upwards of fifty species ; and 

 at other times I have repeatedly enumerated between twenty and thirty species 

 from a single cast. The scythe of the dredge collects from a very limited space 

 over a given area, yet still I doubt much if I ever procured so many species of 

 plants, after having traversed during a whole day the rich woods of the neigh- 

 bouring forest. 



The practical conchologist soon distinguishes, and justly so, between the 

 shells which he finds on or beneath the rocks, in the sands, or among the mud of 

 the shore, and those which are obtained at different depths away from the shore ; 



B 



