1881.] LAKES TANGANYIKA AND NYASSA, ETC. 277 



brackish. The flavour is unpleasant ; and when other water is pro- 

 curahle, that of the lake is not drunk by the natives. 



Two of these most remarkable shells {Limnoirochus thomsoni and 

 L. hir/d) possess all the general outward aspect of the marine genera 

 Trochus and Echhiella ; and the third has a wonderful resemblance 

 to Syrnola in the Pyramidellidse. Moreover Melania nassa (a very 

 variable form) and M. horei (on the contrary, with very constant 

 characters) have much more the look of marine than lacustrine spe- 

 cies ; and it is very probable that when their animals are known they 

 will exhibit some anatomical diiferences which will necessitate their 

 removal from the Melaniidse. In describing the remarkable geuus 

 Tiphobia in my former paper I was unable to give any account of the 

 oi)erculum. Fortunately one of the specimens brought home by Mr. 

 Thomson contains that ajjpendage ; and its structure shows that the 

 species is Melanoid, as was originally surmised. The same defect iu 

 the description of the Faludina-\\ke Neuthauma is now supplied; 

 for several of the specimens contain opercula, which prove to be 

 similar to that of Paludina. 



Altogether thirty species are now known to inhabit Tanganyika. Of 

 these seventeen are apparently peculiar to it, nine having been recorded 

 from other localities, chiefly more northward, in Nilotic regions. Two 

 of these (Limncea natalensis and Melania tuberculata) also occur in 

 Lake Nyassa ; and certain shells which appear to be varieties of Cor- 

 bicula radiata and Unio nyassaensis also inhabit both lakes. Only 

 two additional species are now included in the Nyassa fauna — one a 

 new Ampidlaria (a genus not previously recorded from that lake), the 

 other the well-known Lanistes piirpureus — thus raising the total 

 number of its known species to twenty-seven. 



Of the land-shells hereafter described 1 would call special attention 

 to the Bulimus notabUis, quite unlike any other African form, and to 

 Streptaxis giyas and S. craveni, the former being the giant of 

 the genus. 



1. Cyclophorus wahlbergi, Benson. 



Cyclophorus wahlbergi, Pfeiifer, Cou.-Cab. pi. 50. f. 17-19; Reeve, 

 Con. Ic. f. 81. 



Hab. Between Lake Nyassa and the east coast {Thomson), 

 This well-known South-African form has not, I believe, been re- 

 corded from so northern a locaUty ; but two other species which are 

 very similar have been described : — one, C. magilensis, Craven, from 

 Magila, which I think may prove to be only the young state of this 

 species; and the other C. hildebrandli. Martens, from Ukamba, which, 

 although in general aspect very like, still diff'ers in its greater size 

 and fewer whorls. In Reeve's figure the aperture is represented 

 unusually large. 



2. Cyclostoma insulare, Pfeiffer, var. (Plate XXXII. figs. 

 1, 1 a.) 



Cyclostoma insulare, Pfeiffer, Proc. Zoo). Soc. 1852, p. 64; Con- 

 chyl.-Cab. p. 351.no. 368, pi. 45. figs. 5, 6 ; Reeve, Con. Ic. fig. 41. 



