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



large cavity of a similar kind within the calyx is the type hitherto known as Actinometra 

 robusta, of which I wrote as follows : T — "Just above the dorsal surface of the radial the 

 axial furrow occupying the median line of its internal face gives off a large horizontal 

 diverticulum into the substance of its calcareous tissue, which extends outwards for some 

 distance between the central canal and the dorsal surface of the radial ; and, like the axial 

 furrow, or canal as it is in the natural condition when the rosette is in situ, encloses a 

 dorsal extension of the body-cavity or coelom. " 



In Actinometra robusta, therefore, the radial axial canal, though it terminates 

 blindly at the top of the centro-dorsal, communicates with a large cavity in the lowest 

 part of the radial ; while in Antedon quinduplicava this cavity is outside and below the 

 first radial, between it and the centro-dorsal. 



The presence or absence of this cavity may prove to be a point of some importance 

 in assisting a future decision, as to whether Antedon quinduplicava is or is not identical 

 with Antedon anc&ps, a question which must wait till a further supply of material 

 is obtained. 



Note on Antedon Jluctuans. 



Since the printing off of pp. 94-96, which contain the description of Antedon 

 jluctuans, I have had occasion to revise the tridistichate species of Antedon that have 

 been classified as having articulated radials. Among these is Antedon elegans, which was 

 described by Bell in 1884 from three specimens obtained by the " Alert " at Port Molle 

 in Queensland. 2 



I had made a cursory examination of the greater part of the Comatulse dredged by 

 the " Alert " some time previously, but had not been able to identify any representative 

 of the type which appeared in my working list of new Challenger species as Antedon 

 Jluctuans. Subsequently, however, as pointed out on p. 95, I recognised this type in 

 an imperfect specimen from Torres Strait, which was in too mutilated a condition for 

 description with the rest of the " Alert " collection. 



Bell noticed expressly 3 that among the species of Antedon which he did describe in 

 the report, " in no case is the radial axillary a syzygy." 



I have already pointed out, however, on p. 98, that there is a syzygy between the 

 second and axillary radials of Antedon microdiscus, which is one of Bell's new species ; 

 and I now find that the same is the case in all three examples of his Antedon elegans, 

 which I examined in August last for the purpose of definitely making out its relation 

 to the other tridistichate species of Antedon with articulated radials, before drawing up 

 a classification of the group. 



1 Trans. Linn. Soc. Lond. (Zool.), ser. 2, 1879, vol. ii. pp. 86, 87. 



1 " Alert" Report, p. 162. pi. xiii. figs, b, b<i. 3 Ibid., p. 155. 



