The genus Branchiomaldane, represented by a single species vincenti, was founded by Langerhans to contain certain small Polychætes, which he discovered living in sand-covered tubes, among algæ, on the northern shore of Teneriffe. Professor Mesnil has since found specimens, inhabiting mucous tubes situated on the lower side of the calcareous alga Lithothamnion, in rock-pools at St Martin, near Cape la Hague, and has given an account of some of the structural features of these worms, which he showed to be adult and hermaphrodite. Professor Fauvel considered B. vincenti to be a dwarf Arenicola, arrested in development; he therefore merged Branchiomaldane with Arenicola, and designated the worm Arenicola vincenti. The writer has investigated the anatomy of several specimens of this worm, kindly sent to him by Professor Mesnil, and has concluded that the genus Branchiomaldane should be retained; the original name of the worm—B. vincenti—is therefore employed in the following account.