The Bopyrid described in the present paper was detected by my friend Mr. Buitendijk, when examining a lot of the large Palaemon carcinus, offered for sale on the passar (market) of Tandjong-Priok. He collected no less than thirteen specimens of this parasite, but I regret that the exact number of Palaemonidae examined by him is unknown to me. Thanks the careful investigations of Giard 1), Bonnier 2) and Max Weber 3), it is well known that the Palaemonidae of the Malayan Archipelago are especially infested by members of the genus Palaegyge, containing Bopyridae characterized by having rudimentary uropods in the female and the segments of the pleon distinctly separated from each other in the male 4). As far as I know, only seven species are hitherto described, found on six species of Palaemonidae, viz. Palaegyge Borrei and — Weberi (on Pal. dispar), — Bonnieri (on Pal. lar), — fluviatilis (on Pal. lampropus), — de Mani (on Pal. pilimanus), — brevipes (on Pal. endehensis), — incerta (on Pal. bariensis). Female. The largest specimen has a length of 17 mm., its breadth being 18 mm. at the level of the third segment; the smallest one measures only 11 mm. in length and breadth.