298 MB. 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 

 type specimen. These slight diiFerences 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. Ilore were found further north, 

 near Ujiji. 



51. Unio nyassaensis, Lea, vars. (Plate XXXIV. figs. 34-346.) 

 Utiio nyassaensis. Lea, Proc. Acad. Nat. Sci. Philad. 1864, 



p. 108 ; Journ. Acad. Nat. Sci. Philad. 1866, vol. vi. p. 33, pi. \2. 

 f. 32 ; Smith, P. Z. S. 1877, p. 719 ; Sowerby, Conch. Icon. sp. 224, 

 f. a, b (U. nyassce), Errata and Index (U. nyasscnsis). 



Var. = V. MrUi, 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. 



Hab. Lakes Tanganyika and Nyassa {Thomson.) 



Far. TANGANYTCENSIS (fig. 34 «). 



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. 34S). 



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 vari- 

 eties 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. lurtoni, 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 pos- 

 teriorly very considerably, and also exhibit a distinct sinuation near 

 the posterior end of the ventral margin. The latter feature, how- 

 ever, 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. 



