180 MR. EDGAR A. SMITH ON THE MOLLUSCA [Mar. 6, 



October, when sexually mature individuals swarmed, though none 

 showed any tendency to form buds *), Dr. Cunnington's carefully 

 collected material, on the other hand, showed that reproduction 

 by budding was continued in August, September, December, and 

 February, and that it might therefore reasonably be supposed 

 that it went on during the greater part of the year — if, indeed, it 

 ever ceased. 



The discovery of Limnocnida in other river-basins in Africa 

 had materially weakened the case of those who considered that 

 Lake Tanganyika was the last surviving remnant of a Jurassic 

 Sea. The fact that this Medusa had been found in the Victoria 

 Nyanza by M. Oh. AUuaud and Sir Charles Eliot, and also in 

 the Niger by the late Mr. Budgett, proved that it was another 

 instance of a member of the freshwater fauna characteristic of 

 the Central -African Region, and that it was not peculiar to this 

 one deep-water lake as had been originally supposed. 



Mr. G. A. Boulenger, F.R.S., V.P.Z.S., read a paper entitled 

 " Fourth Contribution to the Ichthyology of Lake Tanganyika, 

 Report on the Collection of Fishes made by Dr. W. A. CurLnington 

 during the Third Tanganyika Expedition, 1904-05." 



This paper will be published entire in the ' Transactions.' 



The following papers were also read : — 



1. Zoological Results o£ the Third Tanganyika Expedition, 

 conducted by Dr. W. A. Cunnington, 1904-1905. 

 Report on the Mollusca. By Edgak A. Smith. 



[Received February 6, 1906.] 



(Plate X.t) 



The small collection of Mollusca obtained by Dr. VV. A. Cunning- 

 ton in Lake Tanganyika does not contain any important addition 

 to the thalassoid series. There are some interesting specimens 

 of Bytlioceras iridescens, tending to show that, like most fresh- 

 water species,' it is subject to considerable vai-iation. In two 

 cases, Edgaria and Giraudia, I have been enabled to describe the 

 opercula, which hitherto were unknown, and the collection also 

 affords one new species of the genus Anceya. The various loca- 

 lities furnished by Dr. Cunnington also add to our knowledge 

 of the distribution of some of the forms. Another matter which 

 may be ref ei-red to in these introductory remarks is the occm'rence 

 together, at the south end of the lake, of both the keeled and 

 unkeeled varieties of Neothauma tanganyicense, which, according" 



* J. E. S. Moore, ' Tanganjdka Problem,' 1903, pp. 298-308. 

 t For explanation of the Plate, see p. 186. 



