246 



THE TANGANYIKA PROBLEM. 



TANGANYICIA, CROSS. T. RUFOFILOSA (FIG. 28). 



Upon the shore rocks and flourishing among the surf 

 and the breakers of Lake Tanganyika there are several 

 species of small molluscs, which in the fauna of the 

 lake fill the place of the Littorinas and Neritinas of 

 the sea shores, and among these littoral forms there 

 occurs in great abundance the animal, to the empty shell 

 of which Cross gave the name of Tanganyicia. In its 

 shell (Fig. 28) Tanganyicia somewhat resembles a small 

 Natica, but it lacks the callous characteristic of most, if 



Fig. 28. — The shell and operculum of Tanganyicia 

 rufofilosa. 



not all, the shells of the true Naticas. In the general 

 arrangement of the parts within the mantle cavity, the 

 character of the snout, head, and tentacles, in the position 

 of the renal, reproductive, and alimentary apertures, and in 

 the character of its gill, this animal (Fig. 29) very much 

 resembles Typhobia ; the osphradium is, however, somewhat 

 foliated at its outer end, and in the female the rectum is 

 provided with a large rectal gland. In both sexes the 

 genital aperture is placed farther back than in any of the 

 preceding forms, and in the male we encounter, for the first 

 time among the halolimnic gastropods, an unmistakable 



