72 Traiisactions. 



Attached to the dorsal surface of the hind end of the foot is the oper- 

 culum, closely underlying the shell so as to be visible only from the side. 

 When the animal is completely retracted it fits close against the entrance 

 to the spiral portion of the shell, and is firmly held there by muscles. 



This characteristic prosobranchiate structure is found in this genus only 

 amongst the Pulmonata. 



The thickened edge of the mantle, which, of course, is fused with the 

 neck, and which is usually called the " collar" (fig. 2, mc), is light in colour, 

 and is very muscular. It does not project beyond the shell during loco- 

 motion, but if the animal is allowed to remain in fresh water the head 

 becomes expanded and the mantle-edge appears under the outer lip of the 

 shell. The upper lip of the pulmonary aperture is then seen fitting into the 

 sinus of the shell. 



The margin of the pulmonary aperture is not a simple circular aperture 

 as in Helix, but the lower lip is produced outwards into an " inferior pallial 

 lobe " {ipl) such as occurs in Chilma according to Lang (1900). This 

 lobe is deeply grooved, the groove being triangular in shape, with the apex 

 directed backwards towards the pallial chamber (fig. 2, g). The anus is 

 situated at the apex of this groove. Hutton (1879) describes and figures 

 the anus as being to the right of the pulmonary aperture, and both Hutton 

 and Quov and Gaimard draw the triangular furrow mentioned above as if 

 it were part of the rectum. The anus is really posterior to the pulmonary 

 aperture, although it is capable of being carried beyond it by the extension 

 of the inferior pallial lobe. When the faeces are passed to the exterior 

 the lips of the triangular groove probably close together, so that it is 

 temporarily converted into a tube. This prevents any faeces entering the 

 mantle-cavity. The inferior pallial lobe is also capable of closing against 

 the upper lip of the pulmonary aperture. 



Internal Anatomy. 

 Organs of the Pallial Complex. (Fig. 3.) 



The most conspicuous organ on the roof of the mantle-chamber is the 

 kidney, which presents several remarkable features. It is pure-white in 

 colour, and occupies the middle region of the mantle, across which it 

 extends obliquelv for about two-thirds of its breadth : somewhat flask- 

 shaped in outline, its apex is situated a short distance from the pulmonary 

 aperture, its broader base close to the left side of the roof of the mantle- 

 cavity. Running along its ventral surface is a narrow band of muscle {mu) 

 which arises from the middle of the hinder edge of the columella-muscle, 

 which is not shown in the figure. The portions of the kidney on either 

 side of this band are of unequal sizes. 



The excretory aperture is a conspicuous longitudinal slit on a papilla 

 at its anterior end (ex), which projects freely from the mantle itself. The 

 wall of the kidney is thick, and internally bears numerous filiform papillae 

 which almost fill its cavity. The excretory products can be seen by teasing 

 up a portion and examining it in the fresh state : they appear as clear 

 spherical vesicles of dift'erent sizes, each of which has a very thin envelope 

 of a protoplasmic nature, surrounding a drop of hyaline, non-granular 

 fluid. In the centre of this are several round concretions of a brownish 

 colour. 



Since the cells of the kidney are not ciliated, they will be unable to aid 

 in the removal of excretory products. Probably the muscle-band which 



