Several specimens of Sasamocochlis sasamorii were collected alive for the first time from Tsugaru Straits. Based on the new material, shell, operculum, radula and jaws of this species are here described. The radula lacks marginal teeth, which is a clear distinguishing character from the North Atlantic species Laiocochlis sinistralis at generic level. In spite of sinistrality, Sasamocochlis does not exhibit close relationships with Triphoridae in observed characters. The geographical distribution of this species is restricted to northern Japan ranging from southern Kuril Islands to the Tsugaru Straits at present. Spongivory was confirmed as in other triphoroideans.

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Two specimens of Perotrochus africanus teramachii were collected from insular shelf of Palau Islands. The molluscan assemblage from there includes Calliostoma belauensis n. sp., Bursa awatii, Collariophila erosa, Fusinus pilsburyi, and Conus profundorum.

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Diel change of activity, substratum utilization, crawling distance and upstream movement in currents in Semisulcospira reiniana were surveyed at the Kamo River in Kyoto. S. reiniana clearly showed nocturnal activity pattern in the slow-current area. They used the underside of stones or the inside of sediment as resting sites in the slow-current area. Such resting bouts were long. The substratum utilization during their active periods was biased to sand-flat and mud-flat surface when mud accumulated. In the fast-current area, snails mainly used the exposed surface of stones and sand as resting sites, and the resting bouts were short and intermittent. The mean crawling distance per night was about 2 m in the slow-current area and 1 m in the fast-current area. The indigenous snails do not have a tendency to migrate either upstream or downstream, but snails transplanted into a current faster than the current of their original habitat had a tendency to migrate only downstream. S. libertina occurring in the fast current area showed the same activity pattern as co-existing S. reiniana. Some points that differ from previous studies are also discussed.

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The preference of the arboreal snail Euhadra amaliae for tree species was studied in relation to feeding behavior. When the snails were released at the bases of H-trees and L-trees, defined by the number of snails found in 1994 (H : ≧8 ; L : ≦2), they remained for longer period on H-trees than on L-trees. It suggests presence of preference for tree species in the snails. In the laboratory experiment where branch-cut was given to snails, the snails tended to occur on H-trees more frequently than L-trees. But in the laboratory experiment where only leaves were given, grazed leaf areas did not differ clearly between H- and L-trees. In the field, E. amaliae was commonly observed grazing the surface of trunk and branch but grazing of leaves was rare. Thus, the preference of E. amaliae for tree species cannot be explained by food value of the tree leaf itself.

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Eostrobilops nipponica reikoae n. subsp. (Strobilopsidae), from Osaka, is described. E. n. reikoae differs from nominate subspecies, E. n. nipponica by its distributional area, smaller size, a stout shell and more darkish red-brown color. Eostrobilops, so far only known from Central Japan, is for the first time recorded to occur in Western Japan.

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To clarify the taxonomic status of two forms (Awajichihiro and Yaminonishiki) of Hirase's scallop Volachlamys hirasei, age and growth were examined as the third report of series studies. Circular annuli on the shell surface were used as an age character. Seasonal changes of marginal growth rate (MGR) of the two forms suggested that annulus formation occurs once a year, from March to June ; the annuli are regarded as winter rings. Relationship between shell length at age t (L_t) and that at age t+1 (L_<t+1>) corresponded well with a linear regression of Walford growth transformation in the both forms. The von Bertalanffy growth formulae led from parameters of the transformation were as follows : Awajichihiro form : L_t=56.95 (1-e^<-0.244(t+0.404)>) Yaminonishiki form : L_t=61.64 (1-e^<-0.216(t+0.378)>) Parameters of the Walford growth transformation between the two forms indicated significant difference at the L_t coefficient which indicated growth rapidity, the Yaminonishiki form growing more rapidly than the Awajichihiro form. This might be caused by the conchological differentiation between the two forms.

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To clarify the taxonomic status of two forms (Awajichihiro and Yaminonishiki) of Hirase's scallop Volachlamys hirasei, genetic characters by isozyme analysis were examined as the fourth report of series studies. Since fitness for Hardy-Weinberg equilibrium by chi-square tests indicated no significance at any polymorphic loci in Awajichihiro form, Yaminonishiki form and both the forms pooled, no evidence that the two forms were distinct reproductive populations was recognized. Also, there were no significant differences between the two forms in the values to indicate genetic features and allelic frequencies of the 24 loci examined. The genetic distance (D value) between the two forms indicated 0.0002, being in the level below inter-local population or the same species. The results strongly suggested that the Awajichihiro and the Yaminonishiki forms belong to a single reproductive population, namely the same species, and the morphological variabilities are regarded as phenotypes of the genetic polymorphism. The taxonomic status was decided as follows : Hirase's scallop (Awajichihiro-gai) Volachlamys hirasei (Bavay, 1904) Awajichihiro form V. hirasei var. awajiensis Yaminonishiki form V. hirasei var. ecostata

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