Fifteen species of Mysidacea and thirty-two species of Euphausiacea were identified from 164 samples collected during the four cruises of T. S. Oshoro Mam of the Hokkaido University in the northern part of the Eastern Sector of the Indian Ocean and the Great Australian Bight in southern summer, 1962-1965. Samplings were made by vertical hauls with an lOS net or a Norpac net, and by simultaneous horizontal tows with several numbers of 50 cm square or 56 cm ring closing nets.

Among these 47 species, Paranchialina angustus, Nyctiphanes australis and Euphausia sibogae showed characteristically limited regionality in distribution. The former two species occurred only in the Great Australian Bight. E. sibogae occurred at 21 stations located in the northern part of the Eastern Sector of the Indian Ocean, specially at that in the south of Java Island. This species, however, was found from 430 m to 2976 m depth in daytime, while it was captured in upper 200 m at night. E. sibogae has never been recorded in literature from the Indian Ocean but only from neighbouring waters of East Indies (Hansen 1910) and of Great Barrier Reef (W. M. Tattersall, 1936). This suggests that the occurrence of E. sibogae in the present area is due to prevailing inflow of the Banda Intermediate Water (Rochford, 1964,1966) from the north of the Lesser Sunda Islands into the eastern Indian Ocean.