236 THE TANGANYIKA PROBLEM. 



the nerves, the pleural ganglia extending posteriorly and 

 ventrally to such a degree that they are almost fused up 

 with the pedal ganglia. In consequence of this, the cero- 

 pedal cords are relatively very much longer than the reduced 

 cerebro-pleural. The otocysts are in the usual position 

 behind and above the pedal ganglia ; and the otoliths are 

 numerous and sharply rectangular. 



The radula of Limnotrochus (Fig. 18) is distinctive of 

 the genus, its most striking feature being the blunt pro- 

 tuberance seen on the outer edge of each lateral tooth. 

 The mouth leads into a very short buccal mass, into the 

 posterior portion of which there open two very diminutive 

 and simply saccular salivary glands. The oesophagus is 

 straight, except for one sharp bend just before it enters 

 the stomach. 



Like that of Chytra the stomach of Limnotrochus is 

 divided into two chambers, the anterior one being con- 

 stricted off from the stomach proper by a thickened and 

 nearly circular annulus. The anterior chamber contains 

 a crystalline style ; the walls of the anterior stomachic 

 chamber, or style sac, are thick, while those of the posterior 

 chamber are, relatively, thin. In the latter, in the stomach 

 proper, there is a conspicuous median fold, which as in 

 Trochus and Chytra becomes duplicated, surrounds the 

 aperture of a bile duct and then passes backward into a 

 very well developed spiral caecum. 



The intestine leaves the stomach on the right, and after 

 characteristically twisting twice round the style sac, passes 

 directly away through the mantle cavity to the anus. The 

 kidney is large, lying below and around the heart, and 

 opens by a minute aperture at the upper angle of the 

 mantle cavity, the heart itself having the normal Tsenio- 

 glossate characters. 



