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Show 1880.] FROM CENTRAL AFRICA. 345 generic forms and unlike any other, either recent or fossil. The former with its spine-bearing whorls calls to mind certain marine rather than lacustrine genera; and the latter, although very vivipariform, yet differs from all the species of that family in possessing a sinuated outer lip and an effuse base to the aperture. Of the terrestrial shells one, Limicolaria nilotica, has previously been recorded from more northern Nilotic regions ; and the same observation applies to five species from the lake, viz. Ampullaria ovata, Planorbis suclanicus, Mutela exotica, Unio niloticus, and AUtheria elliptica. 1. ACHATINA (LIMICOLARIA) NILOTICA, Pfeiffer. Bulimus niloticus, Pfr. P. Z. S. 1861, p. 2 1 ; Mai. Bliit. 1861, p. 14; Mon. Hel. vi. p. 86; Mon. Hel. viii. p. 268 (Limicolaria nilotica). Achatina (Limicolaria^) nilotica, Pfr.; Martens, Mai. Bliit. 1865, p. 196, 1870, p. 32 (as Achatina nilotica); Novitates Conch, iv. pl. 110. f. 1-3. Tiiis species appears to be common in the Upper-Nile region. It was first collected in the White-Nile district, and subsequently by Dr. Schweinfurth near the Gazelle River. A narrowly ovate specimen is 111 millims. in length and only 50 in diameter, and the aperture occupies only a little more than half the length, whilst in a specimen from the White-Nile district it ecpials J7JJ of the total length. 2. ACHATINA (LIMICOLARIA) MARTENSIANA, sp. nov. (Plate XXXI. figs. 1, 1«). Shell rimate, rather solid, oblong, turreted, reddish towards the apex, elsewhere dark purple-red or almost black, variegated with oblique, more or less zigzag, opaque creamed-coloured stripes, some of which extend from suture to suture, others only a short distance from the top of the whorls. The latter are 7\ in number, scarcely convex or almost flat, and very feebly constricted beneath the suture. The upper ones are finely granosely decussated, the last and the penultimate being smooth and merely marked with the oblique incremental striae. All exhibit a fine plication or puckering beneath the suture, beneath which an impressed line is sometimes observable upon the last and preceding volutions. Aperture bluish within, displaying more or less of tbe external striping, vertical, equalling about two fifths of the shell's length. Columella suberect, bluish and dark violet, scarcely forming any angulation at the base with the lower margin of the peritreme. Length 36 millims., diam. 17; aperture 14| long, 8 wide. This handsome shell approximates very closely to A. heuglini of Martens in form, but has certain differences in colour and sculpture, which, however, may prove to be only varietal. A. heuglini, from South Abyssinia and the Gazelle River, is said to be regularly striated, and of a horny lutescent colour flamed with red. A. martensiana, on the contrary, is finely granosely decussated upon the spire, and the coloration is very rich and striking. The dark purplish red, which |