1 5° 



THE TANGANYIKA PROBLEM. 



reaches into which the southern end of Tanganyika 

 expands. In the narrow, surf-swept, and turbulent portion 

 of the lake, which stretches between the north of Cameron 

 Bay and Tembwi, Neothauma is only found in the little 

 bays and sheltered places occurring along both shores, and 

 here the character of the form changes, the double-keeled 

 shell of the former variety being replaced by the elongated 

 type shown on page 261 (b). Northward the lake terminates 

 again in more or less sheltered expanses, like the Gulf of 

 Ubuari, the deep bays near Ujiji, and the extreme northern 

 extremity of Tanganyika. In these the form of the genus 

 again changes, the two more southern varieties being 

 generally replaced by the curious rounded form represented 

 on page 261 (c). The same phenomenon is again remarked 

 in the distribution of the beautiful Typhobia shells of Tangan- 

 yika. In the north we have a type which differs from that 

 in the south. So again with regard to the distribution of 

 the Tanganyika genus Paramelania and its allies ; the 

 shell of Paramelania damoni is represented on page 242, 

 and occurs more or less abundantly throughout the lake ; 

 but in certain areas it is to a greater or less degree replaced 

 by several definite varieties ; one of these, represented on 

 page 238, is so peculiar and well marked as to constitute 

 a new generic type. This form, Bytkoceras, occurs only 

 in the southern half of the lake, and is practically exclu- 

 sively related to Cameron Gulf and the bays which lie 

 opposite the gulf on the east coast. Another variety which 

 is much more closely related to Paramelania damoni is 

 the form Paramelania crassigranulata, and this variety 

 is also restricted to certain areas on Tanganyika, being- 

 encountered about Karema on the east coast of the lake. 

 From these observations it would appear to be indicated 

 that the cause of the production of a greater number 



