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Based upon 114, 000 specimens of prawns and shrimps collected by several small type trawlers from eight localities of the Kii Strait along Wakayama Prefecture, their species composition and comparative abundance as well as the population movement of some commercially important species are revealed. They consisted of 20 species of Penaeidae and 17 species of 6 caridean families. Of these, Metapenaeopsis palmensis is new to Japanese fauna, and Periclimenes tosaensis, Processa kotiensis and Nikoides sibogae prove to be recorded for the first time from the Kill Strait. The dominant species is Trachypenaeus curvirostris in the northern part, Metapenaeopsis barbata from north to middle of the strait, M. palmensis in Tanabe Bay only and Plesionika izumiae in the central part of the strait. Other characteristic species, though not so common, occur in each locality. The two dominant species, T. curvirostris and M. barbata, decrease in number from spring to summer, but there seem to be two peaks of the fluctuation of their catches. One peak appears from spring to summer and may depend upon an increase of the body weight and the other is probably caused by the new recruitments in autumn.

Based upon the material from the Kii Strait, the taxonomy and biology of Metapenaeopsis palmensis (HASWELL) are presented. It is the fourth stridulating species in Japan and is separated from the three other species by having 6-12 ridges, the short inner intermediate strip of the petasma and a pair of large bosses on the sternite of fourth pereiopods in females. Sex ratio is approximately 1:1, and females are larger than males. M. palmensis is abundant in shallow waters less than 30m of Tanabe-Bay, but becomes abruptly rare in deeper waters of the strait, as well as in the far north localities. This species seems to be well settled only in Tanabe-Bay and has the long- and short-term generations. The spawning season continues from June to September and new recruitments occur from July to November. It is one of the commercially important prawns and accounted for about 16-19% of the total catches of small-type trawl fisheries in 1972-1975.

Pandalus gracilis Stimpson, which has been synonymized with P. hypsinotus Brandt, is revived as a good species. Both species occur in the Japanese fauna. It is more closely related to P. prensor Stimpson than to P. hypsinotus. The three species show a number of morphological differences; furthermore P. prensor is the smallest of the three, and P. hypsinotus the largest. The life span of P. hypsinotus is longer than that of P. gracilis. P. gracilis is known to occur rathe abundantly in the southern part of the Sea of Japan, but the commercial value is not high, because of the small size.

Asimple technique for obtaining the well-spread metaphase chromosomes from the regeneration blastema of a prawn is described. The removed regeneration blastema of Penaeus(Marsupenneus)japonicus was treated with a slightly modified air-drying method. The diploid number of chromosomes of this prawn was 86.