170 



J. E. S. MOORE. 



features which exists between these lakes are incapable of 

 greatly modifying the forms they contain. Therefore whatever 

 wide difference in type and mode of distribution is apparent 

 between the faunas of Nyassa and Tanganyika must be the 

 expression of the difference of the animals themselves, and not 

 of the slight differences of condition under which they live. 



In confirmation of this view, we find that all the Nyassan 

 molluscan genera are distributed both in Tanganyika and 

 Nyassa in a similar way, i. e. they are more or less restricted 

 to the coast-line and the shallow, sheltered places, such as 

 creeks and bays. For comparison my observations on the bathy- 

 metric distribution of the molluscs in Tanganyika have been 



Table III. — Bathyraetric Distribution of Molluscs 

 in Tanganyika. 



Halolimnic 

 Group. 



100 200 300 400 500 600 700 800 DOO 1000 



The numbers at the foot hidicate the approximate limits of depth in feet to 

 which the molluscan genera known to occur iu Tanganyika extend, and 

 the thickness of the individual lines shows at what depth eacli genus 

 most abundantly occurs. 



