igi6.] Fauna of the Chilka Lake : Mollusca Gastropoda, etc. 371 



Outer gill. 

 Outer lamella . . Attached to the mantle-lobe, the non-glandular portion 



of the kidney, and to the glandular portion behind the 

 visceral mass ; to the non-glandular portion at the level 

 of the visceral ganglia, and lastly to the mantle-lobe 

 again. 

 Inner lamella \ 



( Attached to the under-surface of the non-glandular portion 

 Inner gill. / f ^.q kidney, and to the glandular portion posteriorly. 



Outer lamella J 



Inner lamella . . Free ; beyond the visceral ganglion attached to the inner 



lamella of the opposite inner gill. 



VI. Digestive System. 



The transverse slit-like mouth lies just behind and towards the ventral aspect of 

 the anterior adductor muscle. 



The oesophagus passes horizontally backwards to end in the stomach. Beneath the 

 ventral aspect of the anterior two-fifths of the oesophagus is a space bounded below 

 by the base of the foot, laterally by the labial palps, and behind by the visceral 

 mass. Just behind the upper and lower lips of the mouth the oesophagus has a 

 cuticular lining continuous with a similar, but less prominent, lining of the stomach. 



The stomach is elongately pyriform in shape, and is rounded posteriorly. Behind 

 and from its ventral aspect is given off a hollow tubular structure, the pyloric coecum, 

 which descends into the visceral mass. The pyloric coecum passes to the right side 

 lying on the inner side of the right wall of the visceral mass. It then curves forwards 

 and passes to the front, lying still on the right side and parallel to the coil of the 

 intestine. It then crosses the middle line and passes to the left side where it ends 

 blindly at a point about midway between the junction of the two anterior loops of 

 the intestine and the junction of the foot with the visceral mass. The position of 

 the pyloric coecum varies slightly with the condition of the foot as regards its con- 

 tractility. When the foot is fully extended, the coecum lies at the same level with the 

 lowest loop of the intestine, but when it is more or less retracted, it lies above the loop. 



The intestine begins from the ventral aspect of the stomach just in front of the 

 origin of the pyloric coecum. It passes forwards and a little downwards along the 

 right side of the middle line and curves downwards and then backwards in front of 

 the base of the foot. It then runs backwards along the left side of the middle line and 

 then bends upwards lying on the inner side of the first loop. It then takes another 

 curve and passes a little forwards and then suddenly turns backwards and again 

 downwards and forwards, and passes on straightly forwards crossing the middle line 

 to the right side into the foot to the junction of its anterior two- thirds and posterior 

 one third, where it bends downwards and backwards beneath the pyloric coecum. 

 Lastly the intestine curves round the posterior end of the stomach to reach the pos- 

 terior portion of the dorsal aspect of the latter and then curves out of the visceral 

 mass to enter the pericardial chamber and form the rectum. 



