EEPOET ON THE CEINOIDEA. 99 



The joints of the cirrus figured by Bell ' are much wider than long ; whereas in the 

 Challenger specimen this is only the case in the outer part of the cirrus, some of the 

 lower joints being as long as or longer than wide, and in premature cirri the length is 

 distinctly greater than the width, while the penultimate spine is especially prominent. 



Bell described the second or palmar pinnule of his type specimen as being a good deal 

 longer than the first or distichal one. This is not the case, however, in that dredged by 

 the Challenger; and the pinnules show no trace of the slightly keeled basal joints 

 described by Bell. But the distal edges of the basal joints are somewhat sharp, and 

 beyond the sixth joint they project slightly over the bases of the succeeding ones 

 (PL XXXVII. fig. 6). This feature gradually develops into a blunt slightly spinous 

 process, which is most marked about the fifteenth joint and disappears altogether after the 

 twenty-fifth ; but in the palmar pinnule figured by Bell it is not visible till the eighteenth 

 segment and continues till near the end of the pinnule. It is this feature apparently which 

 led Bell to say — " the more distal joints are provided with a spine or tuft of spines." 



The anal tube of this individual contains a species of Anilocra, the Isopod which 

 was described and figured in Part I. in the same position on the disk of Actinometm 

 rpaucicirra (see Part I. p. 133, pi. lv. fig. 1). 



Antedon, Series II. 



The two outer radials articulated ; ten arms. 



Remarks. — It has been pointed out already that the number of species of Antedon 

 which have articulated radials and only ten arms is very considerable ; and it therefore 

 becomes necessary for the purposes of specific discrimination to arrange them into groups 

 of comparatively small size. I have had considerable difficulty in effecting this object, as 

 the absence of any axillaries on the arms deprives us of an important aid to classification. 

 By using the characters of the arai-bases and of the lower pinnules, however, I have 

 found it possible to classify most of the ten-armed species of Antedon in five groups, 

 which I propose to call by the names of their more characteristic or best known species, — 

 thus, the Eschrichti-growp, the Tenetta-group, &c. 



The radials and lower brachials have flattened sides. Pinnule-arnbulacra generally plated, . 1. BaMcurva. 

 The rays not flattened laterally. Pinnule-ambulacra well plated, . • • -2. Acoela. 



The first two or three pairs of pinnules long and flagellate, with numerous short and wide 



joints, . . . . . . . . . . .3. Eschricktii. 



The joints of the lowest pinnules, which are often long and slender, are longer than wide, 



frequently very much so, . . . . . . ■ • .4. Tenella. 



The first pair of pinnules are comparatively small, and their joints but little longer than wide ; 



one or more of the second, third, and fourth pairs are longer and more massive, with stouter 



joints than their successors, . . . • • ■ • -5. Milherti. 



1 "Alert" Report, pi. xv. fig. d. 



