1881.] LAKES TANGANYIKA AND NYASSA, ETC. 293 



This is another instance of a species from Tanganyika having 

 very much the appearance of a marine form. At present the 

 operculum and animal are unknown ; and therefore I place it pro- 

 visionally in the genus Melania ; for it approaches in some respects 

 certain aberrant forms of that group, e. g. M, brevis, d'Orbigny, 

 and M. parva, Lea. 



The colour is not uniform in tint ; for beneath the whitish infra- 

 sutural line the brown is paler, then comes a darker zone gradually 

 blending into a paler one. The body-whorl too has an ill-defined 

 basal zone. 



36. TiPHOBiA HOREi, Smith. (Plate XXXIV. fig. 28.) 



Tiphobia horei. Smith, Proc. Zool. Soc. 1880, p. 348, pi. 31. f. 

 6-66. 



When describing this very remarkable form, I was unable to give 

 any account of the operculum. Fortunately, one of the specimens 

 brought home by Mr. Thomson had that appendage adhering to the 

 interior. It is almost black, horny, elongate-subovate, rather con- 

 cave exteriorly, paucispiral in the centre, which portion is surrounded 

 by apparently concentric layers. The lower side has a glossy 

 border, which is broadest on the outer margin, narrow and slightly 

 thickened on the inner or columellar edge. 



It is not sufficiently large to close the aperture of the shell as in 

 the genus Paludina ; and the paucispiral character of the early stage 

 of its growth confirms my original opinion that the species should 

 be classed with the Melaniidse. It is by no means a common shell 

 according to the observation of Mr. Thomson, being restricted to a 

 certain part of the lake, and even there not abundant. The absence 

 of an epidermis is still maintained in the specimens now under ex- 

 amination ; and this very remarkable peculiarity may be considered 

 eventually a suflScient distinction to separate the genus from the 

 Melaniidse. 



37. Neothauma tanganyicense, Smith. 



Neothauma tanganyicense. Smith, Proc. Zool. Soc. 1880, p. 349, 

 pi. 31. figs. 7-7c. 



In this instance also I am enabled to give an account of the oper- 

 culum. It is of a reddish colour, and normally paludinoid, the 

 nucleus being situated about midway between the inner or columellar 

 border and the centre. One of the specimens is unusually acutely 

 carinate around the centre of the body- whorl, and very deep in the 

 suture. 



38. Paludina capillata, Frauenfeld. 



Paludina capillata, Frauenfeld, Proc. Zool. Soc. 1865, p. 659 ; 

 1877, p. 717, pi. 74. figs. 3-4. 



Hab. Lake Nyassa (Kirk) ; between it and the east coast 

 {Thotnson). 



