1881.] LAKES TANGANYIKA AND NYASSA, ETC. 291 



31. Melania (Sermyla) admirabilis. (Plate XXXIV. 

 fig. 24.) 



Melania (Sermyla) admirabilis, Smith, Ann. & Mag. N. H. 1880, 

 vi. p. 427. 



Shell elongate, thick, turreted, whitish, stained by a brownish 

 earthy deposit. Whorls probably about 10, very convex, and much 

 constricted beneath at the oblique very deep suture, unequally bi- 

 partite by a shallow furrow a little beneath the suture, bearing 

 strong obliquely arcuate ribs, which at the upper end terminate iu 

 a tubercle above the shallow groove which crosses them ; they vary 

 in number considerably, in one specimen numbering as few as 

 fifteen on the last whorl, and in another as many as twenty-one ; 

 last whorl with the costse abruptly terminating at the middle, 

 beneath which it is girded by five or six strong concentric lirae, 

 which are of equal thickness and equidistant. Aperture ovate, 

 acuminate above, narrowed and effuse at the base. Columella 

 oblique, arcuate at the lower part, thickened and united to the upper 

 end of the outer lip by a thin callosity. Length 47 millims., diameter 

 14 ; aperture 14 long and 8 wide. 



Hab. Lake Tanganyika {E. Coode Hore). 



This species is remarkable for its solidity, and the strength of the 

 costation. 



32. Melania TUBERCULAT a, Miiller. 



Hab. Lake Tanganyika {Thomson). 



Again this ubiquitous species presents itself. It is without a 

 rival in the extent of its geographical distribution, having been re- 

 corded from Malta, North, East, and West Africa, Lake Nyassa, 

 Madagascar, Mauritius, Syria, Ceylon, Persia, Arabia, Mesopotamia, 

 Siam, Java, island of Formosa, and Australia. The Tanganivka 

 specimen is rather strongly cancellated, and exhibits the red dottino- 

 upon the transverse or spiral ridges. 



33. Melania tanganyicensis. (Plate XXXIV. fig. 25.) 

 Melania tanganyicensis, Smith, Annals, loc. cit. 



Shell small, turreted, solid, almost black, with a broad light-chest- 

 nut band occupying the middle of the whorls ; these are about six 

 in number, flat at the sides, and roundly shouldered above, strongly 

 ribbed, tbe ribs being broad but not much elevated ; the body- 

 whorl is large in proportion to the rest of the shell, and has a few 

 transverse sulci at the base. Aperture al.Tiost half as long as the 

 entire shell. Columella well curved, pale and thickened towards the 

 base. Length Jg millims., diam. 2|- ; aperture 3^ long. 



Hab. Lake Tanganyika {Thomson). 



In this instance also the species is represented by a single speci- 

 men only ; and that too is in worn condition. Its characters, how- 

 ever, are such that it can readily be recognized from allied forms, 

 none of which approximate very closely. Certain varieties of M. 

 polymorpha, a Nyassa species, exhibit a close relationship in form, 



