258 THE VOYAGE OF H.M.S. CHALLENGER. 



by Bell, 1 who described the two allied species Antedon decipiens and Antedon irregu- 

 laris, the former with spiny cirri and no palmars, and the latter with palmars but 

 unarmed cirri. But their other characters, especially the short arm-joints and the 

 lateral projections on the lower pinnules, agree very closely with those of Antedon 

 crenulata. Bell appears to have regarded the absence of palmars in Antedon decipiens 

 and of cirrus-spines in Antedon irregularis, which has palmars, however, as sufficient to 

 separate both these types from Antedon crenidata. They had been dredged by H.M.S. 

 " Alert " on the north-east coast of Australia ; and when in August last I began to revise 

 the tridistichate species of Antedon in the Challenger collection, the descriptions of which 

 had been written five or six years before, I found that a form closely allied to Antedon 

 decipiens and an example of Bell's Antedon irregularis, but without palmars, had been 

 figured on PI. XLVIII. figs. 3-5 and PI. XLIX. figs. 1, 2 respectively. Both alike had 

 been obtained in Prince of Wales Channel, and had formerly seemed to me, as the 

 " Alert" specimens from the same locality did to Bell, to represent two different specific 

 types which could not be referred either to Antedon variipinna or to Antedon crenidata. 

 A third form from the Arrou Islands also appeared to be new, and 1 figured it under 

 the name of Antedon dubia (PL XXXVI. figs. 1-6), not being quite clear in my 

 own mind as to whether its tridistichate condition is the normal one or merely due to 

 regeneration of a ten-armed form, as is so often the case in Antedon rosacea and other 

 species. 



Lately, however, I have made a critical study of all the " Alert " material, and have 

 also reconsidered my descriptions of Antedon variipinna and Antedon crenulata. The 

 result is that I find myself unable to discover any characters which are sufficiently 

 constant to be of specific value as distinguishing Antedon irregularis and Antedon dubia 

 from Antedon decipiens, or any of these three from Antedon variipinna and Antedon 

 crenidata. Bell 2 had himself remarked after describing Antedon irregularis — " This 

 species has some resemblance to Antedon decipiens ; but it may be distinguished from it 

 by (a) the absence of spines from the joints of the cirri, (/3) the broader lower pinnules, 

 and (y) the greater length of the more distal pinnules." He gave no details, however, 

 respecting the relative sizes of the lower and distal pinnules respectively in the two 

 types, and after examining his material I find a difficulty in attributing the difference to 

 anything more than the size of the individual specimens, those of Antedon decipiens 

 being generally smaller than those of Antedon irregularis. The presence of spines on 

 the cirrus-joints of Antedon decipiens, and their absence on the more numerous joints of 

 the cirri in Antedon irregularis, seemed, however, to be good specific characters. But 

 when I came to examine the grey specimens from Prince of Wales Channel, which Bell 

 had provisionally regarded as a variety of the white individuals obtained at the same 

 locality, on account of their cirri being " rather more numerous and more jointed," I found 



1 "Alert " Report, pp. 159-162. . ! " Alert " Report, p. 1C2. 



