Two species of beautifully coloured araneine spiders regarded hitherto as different are often found in the northern part of Japan; one is called Akaonigumo or Red Araneus and the other Daidaionigumo or Orange Araneus. The former has long been identified with Araneus quadratus CLERCK and the latter with Araneus pinguis (KARSCH) in this country. The writer, however, has had some doubt about the justness of this identifica-tion, in that the red species can be found more in accord in its characters with the description of Araneus pinguis than with that of Araneus quadratus. Recently, through the kindness of Dr. M. Grasshoff and Dr. H. W. Levi, he has been given an oppor-tunity to examine some typical specimens of European Araneus quadratus. As a result of his comparative study, he has now come to a conclusion that the red species (Akaonigumo) has hitherto been wrongly identified with Araneus quadratus and that both speiders, red and orange (Akaonigumo and Daidaionigumo), can actually be referred to Araneus pinguis. So far as its shape and structure of male palp (embolus, conductor, median apophysis and terminal apophysis) and those of female epigynum (scape and posterior lamellae) are concerned, Araneus pinguis is clearly distinguishable from Araneus quadratus, but it must be admitted on the other hand that the former has some notable affinity with the latter, too. Consequently, it is considered highly possible that Araneus pinguis may be either a geographic variation or a subspecies derived from a common ancestral stock. For the time being, however, the writer still prefers to regard Araneus pinguis as an independent species for the following reasons. 1. It is not definitely known yet whether Araneus quadratus has varied with a cline across Siberia or its distribution is cut off somewhere on the continent. 2. There is much difference in sexual organs between Araneus pinguis and Araneus quadratus, so that the former seems to be far above the level of a subspecies of the latter in its characteristics. 3. The species reported as Araneus quadratus from the eastern part of Siberia (Amur and Kamchatka) may also be Araneus Pinguis. This is because the species from Manchuria and Sakhalin were found identifiable as the same species with Japanese one on the writer's examination. After all, the comparative study of species, European, Siberian and Japanese, is very important, in order not only to give each respective one the correct specific name but also to research the variation, especially the speciation caused by geo-graphic isolation in such a vast area. The key to the solution of all these pro-blems, therefore, may possibly be found from the more profound and detailed study of the Siberian species.