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



with the bases of some arms preserved as far as the second syzygy ; while the other is 

 peculiar in having two distichal series, each consisting of two articulated joints, so that 

 the number of arms is raised to twelve. No trace of this arrangement appears on any of 

 the other nine specimens, but on the other hand there is no indication whatever of its 

 being due to fracture and subsequent regeneration, as is sometimes the case in other 

 Comatulae. A similar variation from the ordinary ten-armed type towards the bidisti- 

 chate group has been described by Dendy 1 in Antedon rosacea, and another is 

 j)resented by Antedon fiexilis (PL XLIL); while Antedon anceps, Antedon dubia, and 

 Antedon multispina are ten-armed species which are occasionally varied by the inter- 

 calation of tridistichate series. 



If the discovery of better preserved material should show that the bidistichate 

 condition of Antedon lusitanica is a natural one and not a mere accidental variation, the 

 type will be worthy of special notice as the only Antedon found in European Seas which 

 has normally more than ten arms. It is already distinguished as the only European 

 Antedon with a plated disk and brachial ambulacra. The condition of the specimens 

 which I have been able to examine is not such as to afford much information respecting 

 the character of the ambulacral plates on the pinnules ; but it is sufficient at any rate to 

 show that sacculi are present and fairly well developed, as is not always the case in 

 species which have an ambulacral skeleton. 



Antedon lusitanica was dredged at 740 fathoms in the East Atlantic, and its nearest 

 ally is undoubtedly Antedon breviradia, from 630 and 1350 fathoms in the South 

 Pacific (PI. XIX). Both species have short and wide second and third radials, Antedon 

 lusitanica especially so, while in most examples of this type the margin of the axillaries 

 and first brachials is much less rounded than the rest of their dorsal surface, and seems 

 to stand off from it as lateral processes, a character which is scarcely perceptible in 

 Antedon breviradia. The first pinnules of the two species are also different. The keels 

 on the inner edge of their lower joints in Antedon lusitanica are less prominent than in 

 Antedon breviradia, but at the same time they are more distinctly separated from one 

 another than is the case in that type ; while the lower cirrus-joints are relatively longer 

 (PL XIX. figs. 1, 2 ; PL XXXIX. fig. 3). 



5. Antedon breviradia, n. sp. (PL III. figs. 4, 5, a-c; PL XL fig. 5 ; PL XIX.; PL 

 XX. figs. 1, 2). 



Specific formula — A.—. 



Centro-dorsal hemispherical or bluntly concave, roughened at the dorsal pole, and 



bearing fifteen or twenty cirri. These have forty to fifty joints, or a few more, of which 



1 Description of a twelve-armed Comatula from the Firth of Clyde, Proc, Roy. Phys. Soc. Edin., 1886, vol. ix. 

 p. 180, pi. x. 



