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Show 1890.] MARINE MOLLUSCA OK ST. HELENA. 263 from some others which closely approach it in outline. Most of the specimens are rather smaller than that of which the dimensions are given above, and have an average length of 6^ millimetres and a diameter of 2f. All of this smaller form are blotched irregularly with pale brown, and have a more or less distinct interrupted pallid zone at the periphery, and white spots below the suture. The larger form is ornamented with numerous longitudinal light brown lines, which vary in thickness, and are connected, more or less, by short transverse ones, producing somewhat the appearance of an indistinct network. NASSA SANCT^-HELEN-E, A. Adams. A series of about forty specimens of Nassa from St. Helena makes it extremely difficult to decide to which species they should be assigned. Some exactly resemble Adams's type (Reeve, Conch. Icon. fig. 188), whilst others appear altogether different, the form and sculpture being very variable. The typical form may be thus described :-Shell elongate, with a rather acutely produced spire, of a dirty whitish colour, with a dark brown line interrupted by the costae around the middle of the body-whorl, also one above near the suture, and another round the base, both being less clearly defined and not so regularly interrupted as the median line ; whorls 8, the three apical smooth, glassy, very convex, the rest narrowly somewhat excavated or concave above, then moderately convex at the sides; sculpture consisting of 10-12 slightly oblique strongish costae, a little nodose at the angle of the concavity, and of spiral sulci, which are well defined and cover the whole of the spire, but become a trifle obsolete on the central part of the body-whorl ; outer lip thickened by abroad external varix, marked with a brown spot, the termination of the central interrupted line, and furnished within with about a dozen fine lirae; columella covered with a callus, with a small elongate narrow tubercle above and several irregular transverse rugosities and tubercles from thence downwards. Length 12 millim., greatest diameter 6|. The principal variations consist of differences of form and colour, in the number of costae, and in the greater or less development of the spiral grooving. When tbe spiral sulci are strongly marked, tbe costae become somewhat nodulous as in A7, incrassata, Strom, with which species Jeffreys, in his account of Mr. Melliss's shells, associated two specimens obtained at St. Helena, and placed in the British Museum by that gentleman. Not one of the St. Helena shells has the canal stained with black like the majority of specimens of incrassata. NASSA CINCTELLA, A. Adams. Hab. St. Helena, 20 fathoms, sandy mud (Adams). The two specimens in Mr. Cuming's collection are all I have seen of this species. It is rather like the West-Indian N. ambigua of Montagu in its short squarish form, but differs in having less tabulated whorls, and stronger or coarser spiral sculpture. |