VII.—The Pterobranchia of the Scottish National Antarctic Expedition (1902 to 1904).

The genus Cephalodiscus was instituted by M'Intosh for a species, C. dodecalophus, which had been obtained by the Challenger Expedition. After the publication of the full account of this species, by M'Intosh and Harmer (87) in the Challenger Report, succeeding papers for nearly twenty years were all based on the original Challenger material. The subject was in particular re-investigated by Masterman in a series of papers (971, 972, 98, 99, 03). The Siboga report, published by Hakmer (05) in 1905, added three Oriental species to the genus. Schepotieff (05, 07, 08) devoted several papers to a further description of the Challenger material; while, more recently (09), he has described an interesting new species, C. indicus, from Ceylon. In 1906 Ridewood (06) described C. gilchristi from South Africa; and in the following year he gave an account (071) of the two species which had been dredged by the Discovery Expedition; and (072) of the development of the plumes in four species of Cephalodiscus. One of the Discovery species, C. nigrescens, had been described two years earlier by Lankester (05), in a preliminary paper; and Ridewood (12) has recently brought forward evidence to show that this species had been dredged by the Erebus and Terror Expedition in 1841 or 1842. In 1907 Andersson (07) added no less than six species to the genus, in describing the results of the Swedish South Polar Expedition, though we give some evidence (pp. 559–563) to show that one of them, C. inæquatus, is synonymous with C. hodgsoni, which had been described by Ridewood (071) earlier in the same year, from the Discovery collection. The most recent addition to the list of species has been given by Gravier (12), who has published an account of C. anderssoni, a new species which was obtained by the second French Antarctic Expedition.