It was already known that Angaria delphinus atrata varies somewhat in shell shape, and it was obviously distinct in variation of shells basing on the material observed 215 specimens, collected from Southern Izu and Nagashima, Mie Pref. Of these 215 specimens, the lowest individual measured 9 mm. in height, the highest 37 mm., most individuals ranging from 17 mm. to 21 mm., (46% of all specimens) ; the largest specimen 41 mm. in diameter, the smallest 13 mm., most individuals ranging from 22 mm. to 27 mm. (51.6%) ; the mean ratio of height to diameter about 79.9, ranging between 60 and 100 ; these ratios having a tendency to increase with the growth of the shell ; standard deviation±6.861 ; variation coefficient about 8.5%.

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