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



flagdlata, &c, which it somewhat resembles in the very small size of the first pair of 

 pinnules as compared with their successors (PI. XXXVIII. fig. 4). The characters of these 

 pinnules, the shortness of the arms, the large number of cirrus-joints, and the presence 

 of the first radials externally, together with the very slightly wall-sided character of the 

 lower joints of the rays, render it very easy to recognise the type, which has really no 

 close allies among the other bidistichate species. 



The disk is scarcely plated at all, and the brachial ambulacra but slightly so. The 

 genital glands contained in the expanded portions of the large lower pinnules are covered 

 by an imperfect pavement of ill-defined plates, above which the ambulacra are situated. 

 The covering plates are tolerably distinct, but the limestone band supporting them is 

 scarcely differentiated into side plates, except in some of the later pinnules. 



The position of the side plates, however, is indicated by the sacculi, which are 

 also abundant on the brachial ambulacra and extend down on to the outer part of the 

 disk. 



The centro-dorsal of Antedon macroncma varies considerably in its shape. Most 

 commonly it is a thick disk with a smooth dorsal surface and the cirrus-sockets arranged 

 irregularly on its sides, as shown in PL IV. fig. 3a ; but it is sometimes more nearly 

 hemispherical, and sometimes almost columnar, with the sockets disposed in alternating 

 vertical rows of three or four each. 



A similar series of variations in the form of the centro-dorsal is characteristic of 

 Antedon scrobieulata from the Oxfordian of the Jura ; and the whole aspect of the calyx 

 of Antedon macronema is more similar to that of the Jurassic Antedon costata and 

 Antedon gresslyi than that of any other recent Antedon which I have seen. The great 

 difference between the fossil and the recent types is that the basals of the latter undergo 

 metamorphosis into a rosette ; while in the former they persist as prismatic rods between 

 the radials and the centro-dorsal. The positions of these are occupied in the recent form 

 by the rays of the basal star (PL IV. fig. 3c), the ends of which sometimes appear on 

 the exterior of the calyx (PL IV. fig. 3a). The general characters of the radials of 

 Antedon macronema have been already described on pp. 23 to 26, and it is not necessary 

 therefore to refer to them again. 



The type was first discovered by Quoy and Gainiard in King George's Sound, and the 

 Challenger dredged it in Port Jackson, while there are examples in the Sydney Museum 

 from Port Stephens. I have never heard of its occurrence at Port Philip, however, though 

 I have seen various other Comatulse from that locality, where its presence might naturally 

 be expected. 



Apart altogether from its resemblance to certain Jurassic Comatulse, Antedon 

 macronema is remarkable as being a link between the species with the rays flattened 

 laterally and an ambulacral skeleton on the pinnules, and those in which these characters 

 do not present themselves, even as slightly as they do in Antedon macronema ; while its 



