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Show 1881.] LAKES TANGANYIKA AND NYASSA, ETC. 295 so deeply umbilicated and less acutely carinated around the umbilicus. The teeth, which frequently are present within the aperture of the Egyptian species, do not exist in either of the Tanganyikan specimens ; but the character of the rib bordering the peristome is similar in both forms. 43. LIMNJSA NATALENSIS, Krauss. Limna?a natalensis, Krauss, Siidafrik. Moll. p. 85, pi. 5. f. 15 ; Kuster, Con.-Cab. pi. 6. f. 1-3 ; Martens, Mai. Blat. 1866, pi. 3. f. 8, 9. Hab. Lake Tanganyika {Hore fy Thomson). This species has a very extensive range, having been recorded from Natal {Krauss), Abyssinia {Blanford and Martens), Lake Nyassa {Kirk and Simons) ; and from the west side of the continent at Benguela the same species, apparently, has been described under the name of L. orophila. 44. PHYSA, sp. Hab. Lake Tanganyika {Thomson). This genus, not previously recorded from this locality, is represented by a single, probably young shell. It is very much of the same character as P. nyassana, described in the Proc. Zool. Soc. 1877, p. 717, pi. 75. fig. 16-17. However, it is distinct; for on comparison with a specimen of that species of similar size, it proves to consist of fewer whorls, has a less prominent spire, and narrower umbilicus. 45. CYRENA (CORBICULA) RADIATA, Parreyss, var. ? Cyrena radiata, Parr., Philippi, Abbild. ii. p. 4, pi. i. f. 8; Cles-sin, Conch.-Cab. (Corbicula) pi. 28. f. 16-18. Hab. Lake Tanganyika (Thomson). The shells from the lake are more finely and closely ribbed than the specimens from the White Nile described by Philippi, and the the hinge is a trifle stouter, but in all other respects agree very well. The shell figured by Sowerby in a wretched monograph in the ' Conchologia Iconica,' under the name of " Cyrena radiata, Hanley, ? MS." (pi. xi. f. 47 a, b), is quite distinct from this species; but fig. 47c on pi. xiii. may be a bad representation of it. This species was recorded by m e from Lake Nyassa (P. Z. S. 1877, p. 718). On comparing the specimens from that locality with those from Tanganyika it becomes a matter of uncertainty whether they should be regarded conspecific. The shells from the latter lake are longer from the umbo to the ventral margin, and consequently less transversely oblong ; their colour is a deeper violet within, whilst the Nyassa specimens are fleshy-brown, varied by the external umbonal and lateral violet rays. Such being the case, I prefer to consider the shells before m e as doubtfully belonging to this species, until an opportunity occurs of studying this most difficult genus more thoroughly. |