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

 1904). By S. F. Harmer, Sc.D., F.R.S., Keeper of the Department of Zoology 

 in the British Museum; and W. G. Ridewood, D.Sc, Lecturer on Biology in the 

 Medical School of St Mary's Hospital, University of London. Communicated by 

 Dr J. H. Ash WORTH. (With Five Text-Figures and Two Plates.)* 



(MS. received February 15, 1913. Read March 17, 1913. Issued separately July 4, 1913.) 



Introduction. 



The genus Cephalodiscus was instituted by MTntosh 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 (97 \ 97 ^ 98, 99, 03). The Sihoga 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 reccDtly (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 (07^) of the two species which had been 

 dredged by the Discovery Expedition ; and (07^) 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 

 ( 1 2) has recently brought forward evidence to show that this species had been dredged 

 by the Erebus and Terror Expedition in 184 L 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. insequatus, is synonymous with C. hodgsoni, which had been described 

 by Ridewood (07^) 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. 



Full references to the literature of the subject, up to the dates of the respective 

 publications, have been given in the works of Harmer (05), Ridewood (07^), and 

 Andersson (07). A general account of the group has more recently been given by 

 Spengel (12). 



The characters of the coenoecium are so well marked that it appears justifiable to 



* Published by permission of the Trustees of the British Museum. 

 TRANS. ROY. SOC. EDIN., VOL. XLIX. PART III. (NO. 7). 70 



