826 PROF. G. C. BOURNE ON THE [ISTov. 17^, 



of the mantle-cavity has been cut through and largely removed 

 to show the principal organs of the pallial complex. The head 

 is relatively large ; the tentacles short and swollen at their bases ;. 

 the eyes, as in all Neritacea, borne on prominences at the outer 

 sides of the bases of the tentacles. Owing to the abortion of 

 the visceral spire the animal has acquired a secondary symmetry, 

 which does not, however, extend to the more important systems 

 of organs. The right and left columellar muscles, cm.l and cm.7\ 

 are subequal in size and symmetrically disposed right and left of 

 the body. The visceral spire is reduced to a triangular mass at 

 the posterior end of the body. To the right side of the mass is. 

 the ovary, ov. ; the left side is occupied by the stomach covered 

 over by the liver. 



The mouth, situated on the ventral .side of the head, is at the- 

 end of a very short snout, which can be scarcely retractile. The 

 foot is large and oval, occupying nearly the whole of the ventral 

 surface behind the snout : it is surrounded by a rudimentary^ 

 epipodial ridge. The operculum is wedged in between the viscera 

 and the upper surface of the foot, extending as far forward as the 

 posterior end of the buccal bulb. It is functionless, at any rate 

 as regards the closing of the aperture of the shell, bvit it seems ta 

 give support to the muscles of the foot, and retains a rudiment of 

 the apophyses characteiistic of the opercula. of the Neritidfe. 



On the dorsal side, after the removal of the roof of the mantle- 

 cavity, the single bipectinate ctenidium, the post-torsional left, 

 is seen lying obliquely across the mantle-cavity, its base attached 

 to the left side and its free end pointing forward and to the right.. 

 As in most ctenidiate Neritacea, the proximal moiety of the 

 ctenidum is attached by a suspensory membrane to the right and 

 left walls of the mantle-cavity, in consequence of which arrange- 

 ment the posterior half of the cavity is divided into an upper and 

 a lower chamber. 



The heart, enclosed in a spacious pericardial cavity, lies on the 

 left side, just behind and below the posterior end of the left 

 columellar muscle. It cannot be seen in a dorsal view, but its. 

 position is indicated by ^jc. The rectum, after traversing the 

 ventricle, crosses obliquely from right to left just in front of the 

 visceral mass, is partly embraced by the complex mass of accessory 

 genital glands and ducts, g.d, and opens by the anus near the 

 anterior end of the right columellar muscle. The kidney, k. lies 

 between the rectum and the basal half of the ctenidium : it opens 

 by a slit-shaped pore into the lower chamber of the mantle-cavity 

 close to the right side of the base of the ctenidium, but the 

 opening cannot be seen in the drawing. It is perhaps necessary 

 to state here that the kidney is the post-torsional left, as has. 

 been fully recognized by recent authors on Molluscan anatomy. 

 It is therefore the homologue, not of the large functional kidney 

 of other Aspidobranchia, but of the so-called papillary sac of 

 Trochidfe and Haliotida?, and of the rudimentary left kidney of. 

 the Docoe-lossa. 



