Mr. S. P. Woodward on new Freshwater Shells. 337 



gives an outline sketch in the Atlas accompanying the volume. These 

 Mr. Carter considers as " the corresponding forms " of the fossil spe- 

 cies mentioned by Mr. Malcolmson and described by Mr. Sowerby ; 

 but he does not attach any name to them. 



In plate 9 of that Atlas, the species figured No. 19 is, without 

 doubt, the same as what I consider to be the Cypris cylindrica, 

 var. major, of this paper ; and the species figured No. 18 is evidently 

 identical with the Cypris subglobosa. The third species, figured 

 No. 20, differs from any of those collected by Mr. Hislop. W. B.] 



ON SOME NEW FRESHWATER SHELLS FROM CENTRAL AFRICA, 

 BY S. P. WOODWARD, F.G.S. 



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 Gatyptr&a that it would be taken for a sea-shell if its 

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

 thofflyphus, 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 Danubiari 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 columellar 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. 



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, Nyariza, 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. 



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

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



