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XX. On the Nursing Pouch or Chamber of the Chama concame- 

 rata ofGmelin. By John Edw. Gray, £59. F.G.S. fyc.* 



WALCHin the 12th volume of the Naturforscher Journal, 

 of Berlin, described and figured (t. \.f. 7.) a very cu- 

 rious shell, which Chemnitz has since named Chama con- 

 camerata. It has been considered as very rare ; but having 

 lately been brought to this country in considerable abundance, 

 — through the kindness of Mr. Pratt, of Bath, I have been en- 

 abled to examine several specimens which had the dried ani- 

 mal in them : and as the formation of the cavity, which is itself 

 an anomalous structure in Mollusca, and the use to which it 

 appears to be applied by the animal, has not hitherto been 

 described, I shall proceed briefly to describe them. 



The cavity is formed by a folding-in of the middle of each 

 of the valves; and this folding-in does not appear to take place 

 till the shell has arrived at the middle period of its growth. 

 It is marked externally by a groove formed by the coming to- 

 gether of the sides of the fold ; the parietes of the cavity are 

 thin, and marked with the same lines of growth as the valves 

 themselves; the cavities or folds of both the valves are exactly 

 opposite, and when the valves are closed, they meet so as to 

 form a nearly closed chamber, which, although in the internal 

 cavity of the shell, is completely external to the animal; and the 

 contents of the cavity, like when the head is in a double night- 

 cap, are on the outside of the shell. Indeed, the manner in 

 which the cavity is formed may be easily understood by fold- 

 ing a piece of paper to the shape. 



The chamber appears to be used by the animal as a nursing 

 pouch to contain its eggs ; for in all the specimens which I have 

 seen, the cavity of each of the valves contained a group of 

 oval, crumpled, pellucid bodies, adhering together, which, when 

 they were soaked in water under the glass of a microscope, di- 

 lated, became semi-transparent, regularly oval, and had all 

 the appearance of the eggs of bivalve Mollusca ; but they are 

 rather large for the size of the shell. 



This is indeed a remarkable anomaly; for most Conchiferce, 

 as was described by Lister, aerate their eggs in their gills, 

 and then emit them into the water to the protection of Nature. 

 Some freshwater species, as the Cyclades, indeed, appear to 

 keep them in the concave part of their shell, so as to be vivi- 

 parous. I do not know of any instance but the above, where 

 a pouch appears to have been formed for their protection; and 

 what is more remarkable, the other species of the genus Car- 

 dita, to which Lamarck has referred this shell, are un- 

 doubtedly destitute of any thing of the kind. 



* Communicated by the Author. 



XXI. On 



