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 
Xenophora. 
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 Limnotrochus thomsoni. 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 Tympanotomus , which exists elsewhere, and 
the anatomy of which is known, than is the case with the 
