438 (W THE RESULTS OV THE TANGANYIKA. EXPEDITION. [May 4, 



of molluscs of genera ali siuular to those found in Nyasa. In the 

 Victoria Nyauza, in Lake Bavingo, and in several others it is the 

 same. Thus it will be seen that Nyasa contains representatives of 

 all the genera met with in the above enumerated lakes. Some of 

 them contain more, some fewer, jnst as might have been antici- 

 pated from the sort of difference in their physiographical cha- 

 racters. Nyasa in fact contains a generalized series of the generic 

 faunas of these other lakes, and an inspection of these forms is 

 sufficient to show that they one and all belong to well-recognized 

 lacustrine groups. If now, however, we turn our attention to 

 Lake Tanganyika, we find not only the whole list of genera fully 

 represented, but above and beyond this a number of quite new 

 and strange forms : these constitute by themselves an isolated and 

 an intensely interesting series, every member of which, with the 

 probable exception of Neotliauma, would, were not their habitat 

 known, have been regarded without any hesitation as marine 

 forms. But a somewhat closer examination of this group shows, 

 in the first place, that the MoUusca themselves are not very 

 similar to any forms now inhabiting the sea. Typhohia and certain 

 otlier species seem to have certain points in common — their radulse, 

 although differing from every known form, are like each other. 

 The little Gastropod which has been known as the Lythoglyjthus of 

 Tanganyika is certainly not related to that group, but approxi- 

 mates in anatomical characters as a whole to the group of the Para- 

 melanice. This last group is certainly very distinct from that 

 formed by Typliohia and its associates, but its members are quite as 

 peculiar, isolated, and self-contained. A most remarkable variety 

 of this group occurs in the deep waters of Tanganyika, where it is 

 associated with Typhohia, Limnotrocus, and some new species. 

 The true Paramelania exist a little higher up, and the lesser forms 

 of this species infest the barely submerged rocks. So far as I 

 have yet been able to study the anatomy of these forms, they 

 certainly seem to suggest a primitive, simple, or generalized con- 

 dition of their parts. They do in fact bear much the same relation 

 to the typical lacustrine and sea-molluscs that the Ganoids do to 

 the typical freshwater and modern oceanic fishes. This incapacity 

 they one and all exhibit of being associated directly with either the 

 present lacustrine or oceanic faunas, seems to me to point most 

 strongly to their being the persistent or modified representatives 

 of a sea-fauna which must have contaminated Tanganyika long 

 ago. The similarity of various forms of Paramelania to certain 

 fossil shells is a fact which has been already independently re- 

 cognized by White and Tausch, who have called attention to the 

 strong resemblance of these shells to the Perr/idifera' of the American 

 and Southern European Chalk. I may here further point out 

 how closely certain forms occurring in Tanganyika resemble the 

 Purpurincf, of the Inferior Oolite. 



The testimony of the geographical distribution of the fauna of 

 the great lakes of Central Africa and of their morphological 

 characters, so far as I have at the present time been able to go, seems 



