CERIANTHARIA. 



In 1889 Liitken claimed to have made the discovery that C. mcmbranaceus was to be found 

 in the Kattegat. In reality this was a mistake, as the specimens of L tit ken are identical with a 

 species I have described below, P. multiplicatus. 



In addition to the above mentioned Ceriantharia, Levins en (1893) has described a species which 

 he called Cerianthus danielsseni a name which Kings ley (1904 p. 347) had suggested for Daniels- 

 sen's C. borcalis. But in the first place it is identical with C. lloydii, and secondly it seems to 

 embrace the species P. multiplicatus I describe below. The large specimens which Lev ins en speaks 

 of from the Kattegat are probably identical with the forms designated as "borealis" and "membrana- 

 ceus" (see P. multiplicatus). 



The name Cerianthus borealis was given by Verrill (1873) to a form from the Arctic regions 

 of the Atlantic coast of North America. The anatomical structure of this species was dealt with, 

 though very imperfectly, by Kingsley (1904). Another, more southern form was first observed by 

 Agazziz (1859) and described later by Verrill (1862) under the name of Cerianthus americanus. It 

 was investigated anatomically by Me Murrich (1890) and (1910), though not so fully as might 

 be desired. 



Before the first adult, northern Cerianthidae had been described, a larval Cerianthid from the 

 Norwegian coast Arachnactis albida, described by M. Sars ((1846), was already known. In 1862 

 Agazziz found on the North American coast another form, Arachnactis brachiolata, and in 1890 

 Bourne mentioned a larval Arachnactis, which Fowler (1897) described as Ar. bournei. As I do 

 not treat the larval forms in detail here, I refer the reader to my paper on "Actinienlarven" (Nordisches 

 Plankton 1906). 



To these species I have in the present treatise to add three which have not been described 

 before: Pachycerianthus multiplicatus, Arachnanthus sarsi and Botrucnidifer norvegicus: three new 

 genera Arachnanthus, Botrucnidifer and Ceriantheopsis are here described for the first time. 



If we include the North American form C. borealis in our list of the northern and arctic 

 Cerianthidae at present known, we get the following number of adult forms. 



(1) Cerianthus lloydii Gosse = borealis Danielssen = danielsseni p. p. Levin sen, King- 



sley = vermicularis Liitken = lutkeni Andres. 



(2) vogti Danielssen = Cerianthus abyssorum Danielssen. 



(3) borealis Verrill (not of Danielssen). 



(4) Pachycerianthus multiplicatus Carlgren = Cerianthus danielsseni Levinsenp. p. = ment- 



or anaceus Lutken. 



(5) Arachnanthus sarsi Carlgren. 



(6) Botrucnidifer nor-vegicus Carlgren. 



Here belong the following forms whose place in the system it has not been possible to deter- 

 mine 1 ). Possibly one of them may be identical with one of the six already mentioned. 



') Still another Ceriantharia which was obtained by the "Michael Sars" Expedition 1910 (60 57' N. 4 38' W 1098111. 

 clay St. 102 9. 10. 1910), has brown labial tentacles and stomatodaeum, very deep furrows in the distal portion of the 

 column, marginal tentacles twice as large as the labial tentacles, a directive labial tentacle, and the typical arrangement of 

 the mesenteries. As only the most distal part of the specimens was secured they were cut in two by the dredge at 

 the lower border of the stomatodaeum it is impossible to give a precise description of it. It appears however not to be 

 identical with any of the Ceriantharia which I have described. 



