348 



15. On some New Freshwater Shells from Central 

 Africa. By S. P. Woodward, E.G.S. Communicated 

 by Prof. Owen. 



(Mollusca, PL XLVII.) 



The four shells which form the subject of the present note were 

 collected by Captain Speke in the great freshwater Lake Tanganyika 

 in Central Africa. 



The large bivalve belongs to the genus Iridina, Lamarck, — a group 

 of river-mussels, of which there are nine reputed species, all belong- 

 ing to the African Continent. This little group has been divided 

 into several subgenera. That to which the new shell belongs is di- 

 stinguished by its broad and deeply-wrinkled hinge-line, and is 

 called Pleiodon by Conrad. The posterior slope of this shell is en- 

 crusted with tufa, as if there were limestone rocks in the vicinity of 

 its habitat. 



The small bivalve is a normal Unio, with finely sculptured valves. 



The smaller univalve is concave beneath, and so much resembles 

 a Nerita or Calyptrcea that it would be taken for a sea-shell if its 

 history were not well authenticated. It agrees essentially with Li- 

 thoglypkus, — a genus peculiar to the Danube ; for the American shells 

 referred to it are probably, or, I may say, certainly distinct. It 

 agrees with the Danubian shells in the extreme obliquity of the 

 aperture, and differs in the width of the umbilicus, which in the 

 European species is nearly concealed by the callous colunjellar lip. 



In the Upper Eocene Tertiaries of the Isle of Wight there are 

 several estuary shells, forming the genus Globulus, Sow., whose affi- 

 nities are uncertain, but which resemble Lithoglyphus. 



The Lake Tanganyika (situated in lat. 3° to 8° S. and long. 30° E.), 

 which is several hundred miles in length and 30 to 40 in breadth, 

 seems entirely disconnected with the region of the Danube : but the 

 separation may not always have been so complete, for there is another 

 great lake, Nyanza, to the northward of Tanganyika, which is be- 

 lieved by Speke to be the principal source of the Nile. 



The other univalve is a Melania, of the subgenus Melanella 

 (Swainson), similar in shape to M. hollandi of S. Europe, and similar 

 to several Eocene species of the Isle of Wight. Its colour, solidity, 

 and tuberculated ribs give it much the appearance of a small marine 

 whelk (Nassa) ; and it is found in more boisterous waters, on the 

 shores of this great Inland Sea, than most of its congeners inhabit. 



1. Iridina (Pleiodon) spekii, n. sp. (PI. XLVII. fig. 2.) 



Shell oblong, ventricose, somewhat attenuated at each end ; base 

 slightly concave ; epidermis chestnut-brown, deepening to black at 

 the margin ; anterior slope obscurely radiated ; hinge-line com- 

 pressed in front and tuberculated, wider behind and deeply wrinkled. 



Length 4f, breadth 2, thickness If inches. 



Testa oblonga, tumida, extrcmitatibus fere attenuata, basi suba?*- 

 cuata ; epidermide castaneo-fusca, marginem versus nigricante ; 



