OCR Text |
Show 1890.] MARINE MOLLUSCA OF ST. HELENA. 299 be inclined to place this form in the Actceonidm, as recommended Adams, rather than in the Pyramidellida;. Some confusion appears to exist with regard to the genus Mono-ptyyma, judging from the variety of shells which have been placed in it. The original type described by Lea under the name of M. alabumensis is a fossil, and evidently allied to Ancillaria, with which it is associated both by Tryon and Fischer in their recent Manuals. A. Adams published a monograph of this genus in the ' Proceedings of the Zoological Society ' for 1851 (reproduced in Sowerby's ' Thesaurus Conchyliorum,' vol. ii.), including in it a number of species, none cf which, in fact, have any relationship with Monoptygma. He subsequently removed all of these species to other genera, with the exception of M. striatum and M. fulvum. A species very closely allied to these forms has since been described by Lischke from Japan, under the name of M. eximium. As far as I can ascertain, no generic or subgeneric division has been proposed for these species. If as much latitude in variation of form be allowed in the genus Leucotina as in some other genera (e. g., Murex, Triton, Mitrct, & c ) , there is no occasion to establish a new division for these three and allied species, for, with the exception of being more elongate than typical species of the genus, they do not offer any material differences in regard to the aperture, sculpture, or the apical whorls. UMBRELLA MEDITERRANEA, Lamarck? This well-known Mediterranean shell also occurs at Madeira and the Cape de Verae Islands, but it has not previously been recorded from so southern a locality as St. Helena. Krauss1 quotes U. indica as a Cape species, so that I am uncertaiu whether the two young shells from St. Helena should not be referred to that species, if in reality it is distinct from the Mediterranean form. It is stated by Eydoux and Souleyet, in the ' Zoology of the Bonite,' that the animals do not differ, and, as far as I have studied the shells, the two typical forms appear to pass one into the other. TYLODINA CITRINA, Joannis. Tylodina citrina, Joannis, Mag. de Zool. 1834, pi. 36 ; Grube, Ausflug Triest und Quarnero, pp. 58 & 120. Hab. Mediterranean (Joannis, Grube, Monterosato, Sfc.) ; Canary Islands (McAndrew, teste Weinkauff). Only some small specimens, about 7 millim. in length, were obtained. They agree in every particular with the apical portion of large Mediterranean examples with which I have compared them. The minute nucleus consists of about two spirally-coiled whorls, is glossy, vitreous, and laterally inclined. 1 Siidafr. Moll. p. 62. |