296 MR. E. A. SMITH ON SHELLS FROM [Feb. I H, 



46. Pleiodon SPEKEI, "Woodward. (Plate XXXIV. figs. 31, 31a.) 



Pleiodon spe^ei, 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; Kiister's Conch.-Cab. [iridina) 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. {Iridina) fig. 2. 



Iridina nilotica (Ferussac), Sowerby, Zool. Journ. vol. i. pi. 2 ; 

 id. Con. Icon. f. 4 ; Kiister, Con. -Cab. pi. 25. f. 3. 



Iridina elongata, Sowerby, Genera, fig. 1 ; id. Conch. Icon. f. 1. 



Hah. 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 tang any icensis, 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 cor- 

 rectly 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 



