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Show 296 MR. E. A. SMITH ON SHELLS FROM [Feb. \% 46. PLEIODON SPEKEI,Woodward. (Plate XXXIV. figs. 31,3la.) Pleiodon spekei, Woodward, Proc. Zool. Soc. 1859, p. 348, pi. 47- f. 2; Smith, P. Z. S. 1880, p. 350 ; Reeve's Conch. Icon. vol. xvi. f. 2; Krister's Conch.-Cab. (Lridina) pi. 70. f. I. Hab. Lake Tanganyika (Thomson). Of this fine species the present collection contains two specimens- one quite young, and the other half-grown. The younger shell shows that the teeth on the hinge-line are early developed ; and both specimens are broader posteriorly than the adult form and less acuminate at the extremity. The interior of the valves is bluish white, faintly tinged with rose towards the umbones. 47. MUTELA EXOTICA, Lamarck. Mutela exotica, Lamarck, Anim. s. Vert. ed. 2, vol. vi. p. 571 ; Reeve's Con. Icon. (Lridina) fig. 2. Lridina nilotica (Ferussac), Sowerby, Zool. Journ. vol. i. pi. 2; id. Con. Icon. f. 4 ; Krister, Con.-Cab. pi. 25. f. 3. Lridina elongata, Sowerby, Genera, fig. 1 ; id. Conch. Icon. f. 1. Hab. Lake Tanganyika (Thomson). None of the specimens exceeds 3| inches in length; and one or two of them are indistinctly wrinkled perpendicularly across the valves a short distance from the umbones. 48. SPATHA TANGANYICENSIS, Smith. (Plate XXXIV. fig. 32.) Spatha tanganyicensis, Smith, Proc. Zool. Soc. 1880, p. 350, pi. 31. figs. 8, 8a. The specimen figured in the above work proves to be an unusually broad form, having the posterior extremity much less acuminate than in what appears to be the most common or typical form of the species. In describing the young shell I suggested that the narrow rostrated form would become modified as the animal increased it, and that the dorsal alation would also enlarge. This surmise is to a great extent upheld by the series of specimens before me. However, the shape remains much more slender than I supposed; but the dorsal wing does increase considerably. The colour of the epidermis varies with age-in young shells generally being yellowish green, and becoming darker or of an olive-brown when more mature. The form of the anterior end is not faithfully described by me or correctly depicted in the figure of the adult shell. The only full-grown specimen then before me was broken at that particular part. The series now at hand shows that the angle formed by the dorsal margin (which slightly descends near the extremity) and the upward sweep of the anterior boundary is much more acute, the latter sometimes being slightly sinuated just below the angle. 49. UNIO NILOTICUS, Cailliaud. This species has been previously recorded from Tanganyika, in my former paper. Several additional specimens show that the form and general colouring of the exterior of examples from this particular |