OCR Text |
Show 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 bipartite 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 costae 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 TUBERCULATA, 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 recorded 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 dotting 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-chestnut band occupying the middle of the whorls ; these are about six in number, flat at the sides, and roundly shouldered above, strongly ribbed, the 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 almost half as long as the entire shell. Columella well curved, pale and thickened towards the base. Length 7| millims., diam. 2f ; aperture 3£ long. Hab. Lake Tanganyika (Thomson). In this instance also the species is represented by a single specimen only ; and that too is in worn condition. Its characters, however, 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' |