1. Pleurobranchus hirasei n. sp. is proposed for a notaspidean mollusc formerly known from the Japanese waters as Oscanius testudinarius : HIRASE, 1927 or Pleurobranchus (Oscanius) sp. BABA in HIRASE, 1947. 2. Detailed description was made on the external features, colours, jaws, radula and part of the genitalia in order to distinguish this new species from some of the congeneric species of Pleurobranchus.

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Anadara (Scapharca) broughtonii is one of the most economically important arks found on muddy bottom of shallow waters around Japan. The present paper includes the results of observations on the larvae of this species for the purpose of detecting them from plankton collections. Observations were made on morphological characters, viz. the outline, texture, coloration, size, and especially, hinge apparatus of the larval shell. The material used in this study were reared under the controlled conditions in August, 1968, until they reached metamorphosing stage. The results are summarized as follows : (1) The development of the larvae is shown in Table 1. (2) The photomicrographs of the general shape are shown in Plate 4, while those of the hinge apparatus seen from dorsal side in Text-fig. 1. Morphological characters during growth of the larvae are described in detail. (3) The larval shell of this species is so similar to that of a closely allied form, A. (S.) subcrenata, in color and size at the time of metamorphosis. But A. broughtonii is distinguishable from A. subcrenata in having the different outline and the greater numbers of the concentric growth lines. (4) It is suggested that the hinge structure of the larval shells including the ligament and the provincular teeth is one of the most important criteria in identification and classification of the larvae of bivalve mollusks.

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In December, 1968, I had an opportunity to collect many specimens of Trichelix species in Amami-Oshima and Tokuno-shima Islands, south of Kyushu. The keys to the species of the subgenus Trichelix of the genus Moellendorffia from the Amami Islands are as follows : I. Shell smaller than 20 mm in diameter. Penis sheath is abruptly swollen near the gonopore. Flagellum is short and inserted to the epiphallus. Bellows-like part on the vagina or on the stalk of receptaculum seminis. (Trichelix ANCEY, 1887) A. Shell 17-20 mm in diameter. Bellows-like part on the vagina. Stalk of receptaculum seminis about 17 mm long.....eucharistus (PILSBRY, 1901). B. Shell 13-14 mm in diameter. Bellow-like part on the stalk of receptaculum seminis of about 7 mm long.....diminuta PILSBRY & HIRASE, 1905. II. Shell 20-22 mm in diameter Epiphallus without the flagellum. Vagina is flat and of 28-30 mm long. Stalk of receptaculum seminis is slender and short, of about 10 mm long. Bellows-like part neither on the vagina nor on the stalk of receptaculum seminis.....tokunoensis PILSBRY & HIRASE, 1905.

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