THE TANGANYIKA PROBLEM. 237 



The reproductive apparatus of Limnotrochus is similar to 

 that of Typhobia and Chytra. The genital gland lies upon 

 the liver in the upper portion of the spire, whence the 

 genital duct passes without much coiling, until it finally 

 enlarges in the mantle cavity and opens below the anus. 

 The enlarged portion of the genital duct is related to a 

 glandular (?) organ as it is in Chytra, Typhobia and 

 Xeuophora. 



The animal does not appear to be viviparous. 



BYTHOCERAS, MOORE B. IRIDESCENS (FIG. 2 1 ). 



Like Nassopsis, the genus Bythoceras, so far as is at 

 present known, is exclusively restricted to Tanganyika, 



Fig. 20. — Stomach of Liiiniotrochns tkomsoni. The enlarged rectum is seen below. 



and as a member of the halolimnic fauna of that lake is of 

 considerable interest. The shell of this form when adult 

 is distinguished by the peculiar horns above and below 

 the mouth (Fig. 21). It is sometimes covered with a 

 brown epidermis, but more often quite white and naked. 

 Although conchologically so similar to the genera Nas- 

 sopsis and Paramelania, it has, as we shall immediately 

 see, no morphological relation to the former of these types. 

 Bythoceras is also interesting, because it presents us with 

 more numerous points of correspondence with forms such 

 as the genus Tympauotomiis, which exists elsewhere, and 

 the anatomy of which is known, than is the case with the 



