2 3 8 



THE TANGANYIKA PROBLEM. 



majority of the halolimnic forms. Bythoceras is at present 

 represented in Tanganyika by two species, B. iridescens 

 (Fig. 21) and B. minor (Fig. 24), both of which I 

 dredged living at great depths * in the southern portion 

 of the lake. Taking Bythoceras iridescens as our type, 

 we find that when young the shell does not possess the 

 characteristic spines. Nor has it the peculiar pearly 

 thickening of the mouth invariably present in the older 



Fig. 21. — Bythoceras iridescens. The shell front and back (X \). 



forms. In the young condition the shell is extremely 

 similar to that of Paramelania, and I am inclined to 

 think that the figure of Paramelania crassilabris, given 

 by Professor E. von Martens in his work, " Beschalte 

 Weichthiere, Deutsch Ost-Afrikas " (PI. VI. Fig. 38), is, 

 in reality, that of a young Bythoceras iridescens. 



The outward appearance of the animal is extremely 

 similar to that of Cerithium vulgatum, with the exception 



* From 300 to 1,000 feet. 



