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Show 1871.] MR. HARPER PEASE ON POLYNESIAN LAND-SHELLS. 455 above genus. I note that acetabulum, Pse., should be compared to fida, Pse., rather than obolus, Gld., as is done by Dr. Pfeiffer. I add the following new species:- ENDODONTA CELSA, Pse. T. orbicularis, solidiuscula, late umbilicata, tenuissime radiatim creberrime striatula, rufo et albido pallide tessellata; spira elevata, apice obtusiusculo, nucleus rufescenti-fuscus, sutura bene impressa; anfr. 7, convexi, interdum concentrice e/evato-striati, rarissime sulcati aut angulati, ultimus ad peripheriam obtuse angulatus, subtus rotundatus; apertura obliqua, fere circuluris, lamella unica in anfr. penultimo munita. Diam. 7, alt. 3^ mill. Hab. Insula Raiatea. Genus MICROCYSTIS. Microcystis, Beck, Index Molluscornm, 1837, p. 2. Dr. Beck enumerates six species in illustration of the above genus, three inhabiting the West Indies and three Polynesia. The former are II. cubensis, Pir.=trifaciella, Beck (also the type of the genus Cystycopsis, Morch), H. pellicula, Fer., locality doubtful, but of West-Indian form, and H. pidella, Beck, which remains undetermined. These species are globose in shape, ornamented more or less with coloured bands, of a West-Indian type well-known to collectors. The Polynesian species are H. ornatella, Beck, adamsii, Pfr. = filiceti, Beck, and amcenula, Beck, to which I have lately added a beautiful little species from the Marquesas Islands, viz. marquesana, Pse. The above are much smaller than the West-Indian species, and not so globose, excepting the last, and will not, in m y opinion, prove to be congeneric with them. They stand as anomalies in the Polynesian fauna, being confined to islands in the extreme easterly portion of Polynesia, and are not represented elsewhere. It is not improbable that the three species cited by Dr. Beck from Polynesia are varieties of one, as they are all reported from Rapa, a very small island (but 6^- miles long) in the Austral group, about 400 miles south of Tahiti. Dr. Pfeiffer credits adamsii, Pfr., to both Rapa and Pitcairn, which is probably an error. If it occurs at Pitcairn, it is without much doubt distinct from Dr. Beck's species. Authors have lately extended this genus to embrace a variety of forms, especially a large group of thin, fragile, glassy species, widely distributed over the Polynesian and Papuan Islands, and extendiug to Australia. They appear to have overlooked the fact that Dr. Beck recognized them as being distinct from Microcystis, and arranged them under the generic name of HELICOPSIS, Beck. It was injudicious on the part of Dr. Beck to adopt the above name, as it had been used previously by Fitzinger, although the |