In Vol. XVII of this periodical (p. 161, pl. 4, fig. 2) I described and figured as new an Unio, collected by the Zoologist of the Dutch Expedition to Central Borneo, under the name of infrarostratus. Prof. von Martens, whom I sent a copy of my paper, suggested that it might be the same species as U. caudiculatus v. Mart. (Malakozool. Blätter, 1867, p. 16). As this species was not yet figured, and my specimen did not agree in every respect with the description of v. Martens, it was rather easy to make the mistake. Von Martens says: »area postica ad marginem in rostellum parvulum rectangulum procurrente”, and, as the figure in my paper shows, the rostrum is rather large. As to the sculpture v. Martens says: »striae concentricae inaequales, ad angulum posticolateralem in lamellas parvas elevatae”. Now these lamellae are wanting in the specimen I described: only near the lamellose margin, there is something of the kind. Prof. v. Martens had the kindness to send me a photograph of a specimen of caudiculatus of 60 mill., thus smaller than my type, and on closely comparing it with my specimen, I find that the differences may depend only on age. The outline of the photographed specimen agrees perfectly well with a line of growth of my U. infrarostratus and the lamellae, which seem indeed to be very small, may be rubbed off. So I have no doubt of the identity of the two species, but it may be that, on comparison of more specimens and the differences proving to be constant, my species will have the rank of a variety. In any case, however, the specific name must be caudiculatus v. Martens.