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Show 350 MR. E. A. SMITH ON SHELLS [Apr. 20, certainly flatter. The largest of the Tanganyikan specimens exceeds the dimensions given by Martens, and consists of 5J whorls. Its greatest diameter is 18 millims., smallest 15; and the aperture is 5 broad and 5 high. Smaller examples are precisely of the same size as the original type. The colour of the freshest specimens is light horny brown above, and paler on the undersurface. 12. LITHOGLYPHUS ZONATUS, Woodward, Proc. Zool. Soc. 1859, p. 349, pl. 47. f. 3-3c. In both the specimens sent by Mr. Hore the umbilical callosity completely conceals the rimation. The lip and the edge of the basal excavation are remarkably acute. The whorls are four and a half in number, rapidly enlarging, and convex. 13. PLEIODON SPEKEI, Woodward, Proc. Zool. Soc. 1859, p. 348, pl. 47. f. 2; Conchologia Iconica, vol. xvi. f. 2; Krister's Con. Cab. (Iridina), pl. 70. f. 1. Two odd valves only of this fine species are in the collection sent hy Mr. Hore. The larger is of greater length than the specimen described by Woodward, being nearly 5| inches long and 2 | broad ; and the internal nacre is of the same salmon-colour. On the contrary, the second valve is pearly white within, proportionally broader, less sinuated at the basal margin, with the umbo more remote from the anterior extremity, the muscular scars less deep, and the pallial line further within the valve. 14. MUTELA EXOTICA, Lamarck. Iridina exotica, Lamarck, An. s. Vert. ed. 2, vol. vi. p. 571 ; Reeve's Conch. Icon. f. 2. I. nilotica, Sowerby, Zool. Journ. vol. v. pl. 2 ; Conch. Icon. f. 4 ; Kiister, Con. Cab. pl. 25. f. 3. This is the first record of this species from so southern a locality. Only a single valve, about three inches in length, was obtained. 15. SPATHA TANGANYICENSIS. (Plate XXXI. figs. 8, 8«.) Shell transverse, irregularly elliptic, somewhat winged, very inequilateral, gaping considerably anteriorly, and slightly at the opposite extremity, concentrically sulcate; hinge-line rectilinear; anterior end regularly curved, commencing at right angles to the straigbt dorsal margin, and gradually curving obliquely into the base or lower margin ; posterior end rather acuminately produced. The acumination is sharply rounded, and formed by the upward sweep of the ventral curve and the upper lateral slope, which is obliquely subrectilinear, and joins the dorsal line at an angle of about 65 degrees. Epidermis brownish-olive, marked with very fine radiating and close-set dark greenish-olive lines. Hinge with a single thin lamellar tooth in each valve, extending from the umbo nearly as far as and almost in a line with the dorsal margin. Anterior scar large, irregular, indistinctly bipartite ; posterior one also large, transverse. Beneath the hinge-Jine, a little posterior to the umbones, are two or |