Mr. A. Hancock on the Animal of Chamostrea albida. 107 



Cleidothcerus chamoides of Stutclibury, and believing that a de- 

 scription of the animal would be acceptable to malacologists, I 

 have drawn up the following account of it ; which, though 

 imperfect, I trust will assist in determining the position that 

 this anomalous genus ought to have in the classification. 



It will be seen that this animal differs too much from the 

 Anatinidee to be placed with them ; b\it that it seems to accord 

 pretty well with the Chamaceee ; nevertheless I am unable to say 

 whether or not it is a true member of this latter family, for I 

 can find no sufficiently detailed account of the animal of Chama 

 to allow of a critical comparison. Such comparison, however, can 

 very easily be made by any one who may happen to possess the 

 requisite knowledge of that genus. 



It is unnecessary to give any description of the shell, that 

 being already well known ; although it is proper to state that 

 the convex or attached valve is the right, — the flat or free valve 

 the left. » 



On removing the animal from the shell the mantle is found to 

 be rather thick, less transparent than usual, and of a pretty 

 regular, pale brownish colour ; the two lobes, of course, being 

 unequal, corresponding with the iiTegular development of the 

 valves, are united throughout, the pedal and siphonal apertures 

 being the only openings, except a minute orifice to be afterwards 

 described. The borders (PI. III. fig. 1 a) of the anterior margin are, 

 however, free so far back as the anterior adductor muscle {d) ; and 

 a little below this they become closely united for a short distance, 

 the border of the right lobe projecting a little beyond that of the 

 left. This point {b) corresponds to the angle of the shell pro- 

 duced by its adhesion to its support. Just above this point and 

 close to the lower extremity of the adductor is the pedal opening 

 (c), which is small and circular. The muscle fonns the upper 

 margin of the orifice, its fibres being exposed between the bor- 

 ders of the mantle, for more than half its length ; in fact it here 

 becomes the wall of the branchial chamber, closing up, as it 

 were, a large portion of the pedal aperture, and reducing it to 

 its present limited dimensions. Behind the point where the 

 borders of the mantle are united, they (e) again separate, forming 

 a sort of recess external to the union of the lobes, and from 

 which the siphonal tubes (/, g) issue ; this recess extends as far 

 as the posterior adductor [h). From thence up to the dorsal 

 region the mantle-borders are again united, forming in these 

 parts a sharp edge. Immediately below the beak the ossicle [j) 

 passes diagonally through both lobes of the mantle, and is sur- 

 rounded at either end with a membranous expansion {k) ; these 

 expansions are developments of the lobes, and are undoubtedly 

 for the purpose of providing for the growth of the ossicle. Close 



