182 MR. EDGAR A. SMITH ON THE MOLLUSCA [Mar. 6, 



5. Btthoceras iridescens Moore. (Plate X. figs. 1-3.) 



Hah. Niamkolo, south end of lake. 



The series of specimens now available for examination shows 

 that this species, like most freshwater forms, exhibits consider- 

 able variation in size, form, and sculpture. The mvich enlarged 

 figure in the Proc. Royal Soc. 1898, vol. Ixii. p. 452, fig. 1, 

 reproduced in the Proc. Malac. Soc. vol. iii. p. 93, fig. 1, exhibits 

 an extreme development of the anterior or basal spine, such as I 

 have not seen in any specimen. The largest example in the 

 present collection is 44 millim. in length, and the spire is much 

 longer in proportion to the length of the body- whorl than in the 

 shell depicted by Mr. Moore, and the sculpture is altogether finer. 

 A smaller variety, but equally adult, is more strongly sculptured 

 than the large form and only 30 millim. in length. 



6. Bythoceras minor Moore. (Plate X. fig. 4.) 



Hah. Tembwi, west coast, a little below middle, in 20 fath. 



A single specimen only. I am inclined to think that this 

 species will eventually prove to be a variety of ParameUmiia 

 crassigramdata. In the character of the shells, opercula, and 

 radulse there seems to be very little to separate the genera 

 Bythoceras and Paramelania. 



7. Paramelania crassigranulata Smith. (Plate X. figs. 7, 8.) 



Hah. South end of the lake. 



One very large specimen, 37 millim. in length. 



8. Paramelania damoni Smith. (Plate X. figs. 5, 6, 9.) 



Hah. Tembwi, near middle of west coast of the lake, 30 fath. ; 

 Mrumbi, south of Tembwi, 40 fath. ; Mshale, east coast towards 

 the north end of the lake, 25 fath. ; also south end. 



The single specimen from the last locality resembles the variety 

 imperialis rather than the typical form. 



9. Lavigeria' GRANDis Bovirguignat. (Plate X. figs. 10, 11.) 



Hah. Mbete, south end of lake, on rocks in shallow water. 



A few specimens rather smaller than the type (P. Z. S. 1881, 

 pi. xxxiv. fig. 26 a), with the oblique plications less strongly 

 developed. 



10. Edgaria nassa (Woodward). (Plate X. fig. 19.) 



Hah. Kirando, east coast of lake towards the south end. 



A few specimens of a small variety. Operculum similar in 

 character to that of Lavigeria grandis, horny, dark brown, 

 broadly ovate, nucleus marginal, near the lower end, sculptured 

 with fine lines of growth. 



11. Edgaria paucicostata Bourguignat. 



Hah. South end of the lake. 



Two rather large specimens, 21 millim. in length. 



