A new species of the genus Coleosoma (Araneae : Theridiidae) from Japan. Acta arachnol., 33: 45-50 (1985). A new species of the genus Coleosoma, C. margaritum, is described from Japan. A list of the Japanese species of the genus Coleosoma is also given. The genus Coleosoma is distinguished from the other genera by male abdomen with a sclerotized ring covering anterior half of venter and a carina above. Two species, Coleosoma blandum 0. PICKARD-CAMBRIDGE and C, octomaculatum (BOSENBERG et

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... , were recorded from Japan. The former species was first reported by OHNO and YAGINUMA in 1972 and afterward it was collected widely from warmer part of Japan. The latter one was transferred from Theridion by myself in 1982. Recently, another species of this genus was collected by Y. CHIKUNI in Nagano and Iwate Prefectures, Japan. In my close examination, this species is recognized as a new species. Coleosoma margaritum n. sp. Male (Holotype). Total length 2.1 mm. Carapace length 1.1 mm ; width 0.8 mm. Abdomen length 1.2 mm; width 0.8 mm. Measurements of legs as follows (mm) :