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Show 298 MR. E. A. SMITH ON SHELLS FROM [Feb. 15, collected by Mr. Thomson ; and in character it is also intermediate, being less granulose than some, yet hardly agreeing with that of the tvpe specimen. These slight differences are probably modifications produced by difference of locality ; for the shells collected by Mr. Thomson were from the southern end of the lake, whilst those obtained by Captain Speke and Mr. Hore were found further north, near Ujiji. 51. U N I O NYASSAENSIS, Lea, vars. (Plate X X X I V . figs. 34-345.) Unio nyassaensis, Lea, Proc. Acad. Nat. Sci. Philad. 1864, p. 108 ; Journ. Acad. Nat. Sci. Philad. 1866, vol. vi. p. 33, pi. 12. f. 32 ; Smith, P. Z. S. 1877, p. 719 ; Sowerby, Conch. Icon. sp. 224, f. a, b {U. nyassa?), Errata and Index {U. nyasscnsis). Var. = U. kirkii, Lea, I. c. p. 108 ; Journal, p. 32, pi. 12. f. 30. Var. = U. aferula, Lea, I. c. p. 109 ; Journal, p. 34, pi. 13. f. 34. LLab. Lakes Tanganyika and Nyassa (Thomson.) Var. T A N G A N Y I C E N S I S (fig. 34 a). There are but three valves in Mr. Thomson's collection, which I think may possibly belong to this species. They differ from the normal form in being rather longer transversely, of a pinkish-red colour within, and without also, beneath the greenish epidermis. The latter is finely rayed with green. The sculpture is very similar; but the corrugation does not extend quite so far down the valves. Var. from Nyassa (fig. 34b). Mr. Thomson's specimens are more triangular than those collected by Dr. Kirk at the same locality, having the hinder extremity considerably produced and pointed. Like the three valves from Lake Tanganyika, they are rather smoother than typical specimens; and some of them are of the same pinkish-red colour. Although, as a rule, very different in form from that figured by Lea, still great allowance has to be made for the great variation that obtains among freshwater genera, and especially in the outline of species of Unio; and consequently I prefer to consider the shells in question as varieties of this species rather than distinct forms. 52. UNIO TANGANYICENSIS, Smith. (Plate XXXIV. fig. 35.) Unio tanganyicensis, Smith, Proc. Zool. Soc. 1880, p. 351, pi. 31. f. 9, 9a. As in the case of U. burtoni, so also in this species, the specimens now before me differ from the shells described previously. They are less distinctly radiated with green, produced and beaked posteriorly very considerably, and also exhibit a distinct sinuation near the posterior end of the ventral margin. The latter feature, however, exists in some of the typical shells, though in a considerably less degree. They are too, as a rule, narrower from the umbo to the opposite side. The absence of the green lines is to a great extent accounted for by the worn condition of the exterior of most of the specimens ; for as soon as the epidermis is removed they vanish with it, being only epidermal markings. |