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Show 1890.] MARINE MOLLUSCA OF ST. HELENA. 281 peristoma fere continuum, margine columellari paulo prominente, superne torto. Longit. 2\ millim., diam. g. This minute species is very like A. nitidissima of Montagu, but has decidedly less convex whorls, the aperture is broader, and the columellar twist different. The heterostrophe apical coil is also very similar in both forms. ACLIS DIDYMA. (Plate XXIII. fig. 30.) Testa minuta, turrita, albida, imperforata ; anfractus 6, supremus Icevis, convexus, obtusus, cceteri superne declives, subexcavati, dein obtuse angulati, inferne planiusculi, longitudinaliter striati, ad angulum subplicati; apertura parva, ovata, longit. totius 5 adcequans ; columella levissime refiexa, superne subtorta. Longit. 2\ millim., diam. §. Owing to the large size of the nuclear whorl, this species has very gently converging outlines. The columella does not unite above with the outer lip, but appears to be slightly spirally intorted. SOLARIUM PLACENTALE, Hinds, var. Hab. Bay of Magdalena, California. Off Barbados in deep water (Dall for S. peracutum). Three specimens in excellent condition, one alive with the operculum, were dredged by Capt. Turton. This is another insrance of remarkable distribution in this genus. After a careful study and comparison of these examples with the types of S. placentale, and Mr. Dall's description and figures of S. peracutum 1, although slight differences are noticeable, I can but regard all of them as forms of one and the same species. The St. Helena specimens are a little paler in colour than the type; the periphery is perhaps very slightly more acute, as is the case with S. peracutum ; the crenulaiions bordering the umbilicus finer, and the spiral sculpture, more especially on the upper surfaces, is rather more inclined to be granular. The operculum consists of six whorls, which rapidly increase from a central nucleus, and, on the external surface, have the outer margin elevated, forming a sutural keel and thus giving them a concave aspect. The inner surface is glossy and furnished with a strong whitish central elevated process, from which a conspicuous curved ridge arises, forming rather more than a semicircle. The figure of S. placentale in the ' Conchologia Iconica ' is a mere caricature, being both out of drawing and exaggerated in colour and sculpture. The figures in the 'Voyage of the Sulphur' (pi. xiv. figs. 5, 6) are good and of the natural size. The acuteness of the peripherial keel is variable, for, in a second specimen of the typical form, received by the British Museum from Sir E. Belcher, it is sharper and flatter above. SOLARIUM ORDINARIUM. (Plate XXI. figs. 17-17 6.) Testa orbiculo-conoidea, depressa, mediocriter umbilicata, albida 1 Bull. Mus. Comp. Zool. Harvard, vol. xviii. p. 275, pi. xxxiii. figs. 2. 5. |