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Show 1890.] MARINE MOLLUSCA O F ST. HELENA. 305 LITHODOMUS BI-EXCAVATUS, Reeve ? L. bi-excavatus, Reeve, Conch. Icon. pi. 4. figs. 22 a, b. Hab. St. Thomas, West Indies. The shells obtained at St. Helena by Mr. Melliss and named L. lithophagus, Linn., by Jeffreys, do not belong to that species. They may be considered a variety of L. bi-excavatus, in which the two depressions are not quite so distinct as in the type. The chalky incrustation which invests them has a more openly reticulated or spongy appearance at the posterior end. ARCA SANCT^E-HELEN-E. (Plate XXII. figs. 8-8 6.) Testa oblonga, crassa, albida, rufo-strigata et variegata, inferne haud Mans ; valvce solidce, antice oblique curvutce,postice paulo latiores, curvatim truncatce, radiatim costatae, lineisque tenuibus concentricis et transversis decussatce ; costae incequales, subnodosce, anteriores et posteriores crassce, medianae tenuiores pagina interna alba, ad marginem saturate purpureo-fusca postice fortiter dentata ; umbones remoti, incurvati, prominentes ; liga-menti area lata, concava ; ligamentum subrhomboidale, fuscum, sulcis paucis sculptum. Longit. 66 millim., diam. 47, alt. 36. This is a strong, heavy species, belonging to the same group as A. noce, A. navicularis, and the like. It is more solid than either of the above-named species, has the posterior end unsinuated, and the margins of the valves are peculiarly dentate posteriorly, and, when closed, interlock like the valves of Ostrea crista-galli and some others. A few of the ribs near the posterior angle of the valves are very large and strong, and separated by very deep grooves. The form is rather like that of A. subquadrangula of Dunker, but the posterior end is not so truncate and the costae are different. ARCA (ACAR) DOMINGENSIS, Lamarck. Hab. West Indies, Cape Verde Islands, S. xAfrica, Red Sea, Indian Ocean, South Pacific Ocean, Japan, Australia, &c. (Lischke). PINNA RUGOSA, Sowerby. Pinna rugosa, Sowerby, Reeve, Conch. Icon. pi. 26. fig. 50. Hab. Isle of Rey, Bay of Panama (Cuming). Capt. Turton remarks as follows respecting the single broken valve obtained:-" It measured when perfect 19 inches, but I cannot be sure of this identical shell being an island one, as I bought it; but I have seen another just like it, 16 inches long, which was fished up alive and bought by another officer before I heard of it, so this is probably an island one too." Is there some mistake here, or does this species really occur at Panama ? |