1. The variation in the colour pattern of a bivalve, Venerupis philippinarum, was observed, based on numerous materials collected in Onomiti district. According to Ikeda (1893) the pattern is classified into four (banded, marked, wave and white) types. 2. The banded type is characterised by the presence of radial colour bands, and various forms are distinguished by colour band and degree of pigmentation : viz. "bandless, chestnut-, brown-, yellow-, purple-band." In the marked type the pattern consists of irregular patches, which can be divided into "piebald" and "divaricate" groups ; in the wave type the shell is ornamented with concentric, ripple-mark like pattern, in which particular case can be distinguished as "chestnut wave" and "loose wave". The white type is regarded as a kind of albino, but the shell has a narrow radial dark band on the left posterior area. 3. The colouration in the interior of the shell is classified into "purple, purple margin, purple behind, orange, red behind"; these colours occur in conjunction with some of the banded types. 4. The colour types are shown with symbols, and combinations between these colour types are tabulated ; it is probable that these types are exhibited by the corresponding hereditary character. 5. The bilaterally asymmetrical colour pattern is divided as follows : a) Marked type : i) One (right or left) valve is provided with an excessive colour pattern than the other. ii) The corresponding colour pattern is dislocated on both valves. b) White type : left posterior area is deeply pigmented. 6. In the marked type the excessive colour pattern occurs in the same degree in both valves, but in the case of dislocation in colour pattern, the pattern tends to be shifted to the right side in the right valve. 7. The asymmetrical colour pattern in the marked type may be due to the disturbance in the pigmentation mechanism accompanied by the rapid growth of the animal, so that its origin is accidental and exogenous, but it is regarded as of genic origin in the white type, which is unique in the mollusca, and also in the animal kingdom.

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As already known, sexual dimorphism is seen in the shell of the members of Buccinidae (Morse 1877 ; Buccinum undatum). In the materials collected in Hokkaido and north-eastern part of Honsyu (Neptunea, Buccinum, Japelion), the difference is as follows : (1) the male shell is smaller in size, or more slender than in female shell, and also in the genus Neptunea (N. vinosa (Dall), constricta (Dall), lyrata (Gmelin)) the peristome of the female is expanded and more or less reversed, while in male no such expansion of peristome is not observed. Also in both N. vinosa and Buccinum leucostoma (Lischke) the interior of the peristome in male is characterised by the reddish orange colour, while in female it is whitish or yellowish.

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