During the dives of DSRV Alvin in the hydrothermal vent area in the Mariana Back-Arc Basin about 3650 m deep, aggregations of an unusual gastropod were discovered around the vent openings. The description of this snail, Alviniconcha hessleri, gen. et sp. nov. is given. The morphological characters of this species suggest affinities to Trichotropidae or Hipponiacea of the Mesogastropoda but warrant to establish new family.

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Cassis abbotti n. sp. is characterized by a smooth polished shell, a poorly developed parietal shield, a narrow aperture with denticulated inner and outer lips, and a bulbous, paucispiral protoconch. It is possibly endemic to the Chesterfield-Bellona Plateau, where the holotype was taken in 205 m.

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Alcithoe aillaudorum n. sp. is the first Alcithoe known outside New Zealand waters ; it is however not considered a Gondwanian vicariant relict but is probably a recent immigrant that dispersed from New Zealand to New Caledonia via the Norfolk ridge. Lyria exorata n. sp. is known from Capel and Kelso Banks, two submerged flat plateaus surrounded by abyssal depths in the Coral Sea. L. habei Okutani, 1979 is a new record for New Caledonia. Records of other Lyria are reviewed and summarized. Although the distribution of Lyria in the Western Pacific corresponds rather well with the limits of the Pacific plate, this distribution appears to be a result of constraints in larval biology rather than a reflection of the plate tectonic history of the area.

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Many specimens of the scallop were obtained from the early Pleistocene Omma Formation. As the result of conchological examination, it has become clear that these specimens are identified with Pecten byoritsuensis Nomura which was once described from the Byoritsu Beds in Taiwan. This species has many common characteristics with the recent Pecten sinensis Sowerby and may be an ancestral species of the latter.

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Spawning of the chiton Acanthopleura japonica was observed for 72 hours at 23℃ under constant illumination in the laboratory in August 1984. Of sixty individuals caught at daytime spring low tide, two females and five males spawned simultaneously just before the morning high tide peak on the next day, and one female of them released eggs again on the following day. Early development and larval settlement at different temperatures are shown. Intrinsic timing mechanism for spawning is suggested.

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The karyotype of Omphalius rusticus was examined. The chromosome numbers of this species are n=18 and 2n=36. Its karyotype is formulated as follows : 2n=36=22M+12SM+2ST, NF=72.

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The relative geographic occurrence of Mytilus californianus along the Pacific coast of Baja California, Mexico, is mapped. We present the comparative density of M. californianus in the 3 intertidal zones (high, middle, low) and of the different size classes (settlers, seedlings, juveniles, and adults).

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