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Show 1881.] SHELLS F R O M SOCOTRA. 253 5, well rounded. Aperture obliquely and broadly ovate, angular above, suboblique. Peristome thick and solid, particularly on the columellar margin, where it spreads out and completely conceals the umbilicus; this is a greater development and exaggeration of the angulate notch which is to be seen in the next two species from this island. Operculum situated well within the aperture, flatly concave in front, shelly, smooth, of about 3| whorls, nucleus sub-central. Size of largest specimen-major diam. 59*5, minor diam. 5*1, alt. axis 31-5 millims. Largest size given by Pfeiffer-major diam. 41-0, minor diam. 34-0, aperture 19x16 millims. Example figured- major diam. 2*15, minor diam. 1*7, alt. axis 1*35 inch. ,, ,, 54, „ „ 42*5, „ 34-0 millims. Small var.- major diam. 38, ,, „ 30-7, „ 18*5 „ „ 1-32, „ „ 10, „ 0-53 inch. Animal not yet examined. [" Very common on the limestone plains from more than one locality."" (I. B. B.)] O. guillani, Petit, is a small form, diameter 26 millims., very similar in the expansion of the columella-notch over the umbilicus, from Mogadoxa on the N.E. coast of Africa, 250 leagues distant from Socotra. OTOPOMA BALFOURI, n. sp. (Plate XXVII. figs. 2, 2 a.) Shell globosely turbinate, solid, very openly umbilicated, ribbed regularly and spirally throughout; but the ribbing does not extend within the umbilicus ; colour white; spire pyramidal, decollate usually for 1^ whorl; suture well impressed; whorls 4, well rounded; aperture subvertical, ovoid, angular above; peristome continuous, solid, and reflected slightly on the outer margin, less solid on the columellar side, which presents a slight dentation with angularity just below the upper inner margin, well rounded below. Size :- Major diam. 55*0, minor diam. 40*0, alt. axis. 22*0 millims. 2-16, „ „ 1-58, „ 0-87 inches. Dwarf var. major diam. 32'8, „ „ 26-5, ,, 14 millims. [" Common on the land towards the east end of the island : this portion is elevated over 700 feet and is of limestone." (I. B. B.)] This species is very close to O. auriculare, Gray, of which the habitat is unknown, but the columellar margin is more expanded and the ribbing is coarser and more distant than in O. balfouri. Cyclostoma albicans, Sow, apud Gray, Zool. Beechey's Voy. pi. xxxviii. fig. 30, p. 146, is said to inhabit some of the islands of the Southern Pacific, which I do not believe is correct. The description agrees with this shell; but no dimensions are given, and the |
