296 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



are deeply pigmented with green. With reference to this organ I feel 

 I cannot add anything to the excellent account given by F. Bernard (5), 

 and must admit I hav^e been unable, from want of time and material, 

 to give it very detailed attention as far as the histology is concerned. 

 The large central nerve ganglion can be made out without difficulty 

 on account of its being unpigmented. 



The ctenidium (Fig. 1, Ct.) is of the usual monopectinate type, and 

 is situated on the roof of the pallial chamber, to the left of and close 

 to the osphradium. At its base runs the thin-walled vessel carrying 

 the aerated blood to the heart. It is faintly pigmented with pink, 

 and is attached to the mantle, from end to end, by more than half its 

 under-surface. It finishes some little distance from the free edge of 

 the mantle, and is so placed as to receive directly the inflowing stream 

 of water from the syphon. 



The syphon is short, and, as far as I could make out, has no 

 appendages. It is formed by a fold in the mantle, which is much 

 thicker on the left-hand side of the animal than on the right. 



Hypohranchial Glands. These do not appear to be particularly well 

 developed, though they cover a considerable area of the under-surface 

 of the mantle in the neighbourhood of the ctenidium. They are 

 formed by a number of folds of the inner membrane, very slightly 

 pigmented with pink. 



The pallial chamber was filled with a very tough mucous. 



Nepliridial Opening. This is placed at the back of the pallial 

 chamber, in the wall separating the chamber from the nephridium. 



Nephridium. Of large size, and rendered distinctly visible from the 

 outside by a purplish tint when the animal is looked at after being 

 taken out of the shell. It is in the form of a sac situated to the riglit 

 hand of the pericardium, immediately behind the pallial chamber, 

 from which it is separated by a thin and nearly transparent membrane, 

 in which, as before mentioned, is situated the slit -like excretory 

 orifice, surrounded by muscular fibres forming a sphincter. No part 

 of the excretory tissue appears to be attached to this thin division- 

 wall. The nephridium is traversed by the intestine, by which it is 

 practically divided into two lobes. The internal structure of the 

 organ is very complicated and has a more or less honeycombed 

 appearance and a spongy texture, the divisions being formed by the 

 ramifications which appear to be connected to two longitudinal axes, 

 one on each side of and running parallel to the traversing intestine. 

 The colour of the gland is brownish. 



Reno- Pericardial Canal. Unfortunately the pericardium broke 

 away owing to the weight of the visceral sac, and I could not trace 

 the canal. Perrier states that it is very short, being only 2 mm. long 

 and "5 mm. in diameter. 



The nepliridial gland is distinct both in colour and appearance 

 from the nephridium, and occupies two sides of the sac, namely, those 

 bordering the pericardium and the anterior border. Its canals ramify 

 more or less under the general mass of the nephridium. 



