REPORT ON THE CRINOIDEA. 249 



Remarks. — Three individuals of this species, and also three larvse, all with ten arms, 

 were obtained at Station 344, near Ascension, and have been already described. 1 But 

 another individual from the same station must be noticed here from its having two 

 tridistichate series. It resembles Antedon ancjustieahjx and Antedon iniequcdis in the 

 syzygial union of the two lowest brachials, but it differs both from them and from the 

 other tridistichate species in its spiny calyx and in the characters of the pinnules. The 

 first pinnule (PI. LXIX. figs. 2, 3) consists of rather massive joints with their inner edges 

 cut away a little and the outer sides slightly flattened, presenting, in fact, the same 

 characters, though in a less prominent form, as the first pinnules of Antedon valida, 

 Antedon incerta, and their allies among the ten-armed species of the Basicurva-gvoi\-p 

 (PI. XV. figs. 5, 6 ; PI. XVIII. fig. 5). The first pinnule of Antedon multispina is 

 much larger than its successor, a character which distinguishes the type both from 

 the species just mentioned and from the other members of the Grramdifera-growp, 

 from which it also differs in the uniformly expanded shape of the large joints of the 

 genital pinnules. 



Station 135g, off Tristan da Cunha, yielded a single mutilated Antedon (PI. L. 

 figs. 3-6), which after some consideration I have decided to refer to this species, though 

 I was at first inclined to place it elsewhere. The cirri are generally similar to those of 

 the more northern form (PI. XIII. fig. 1 ; PL L. fig. G), but may have as many as 

 thirty-five joints, while the number does not exceed thirty in the smaller and premature 

 individuals from near Ascension. The latter do not show the first radials externally 

 (PI. LXIX. figs. 1, 2), but they are visible in the larger calyx of the southern variety 

 (PI. L. fig. 3), which is also less distinctly spinous than that of the northern individual, 

 and the same is true of the arm- and pinnule-joints. 



The first pinnules of the southern form have somewhat the same flattened appearance 

 on their outer sides as is traceable in that from Ascension (PI. LXIX. figs. 2, 3), and 

 is more marked in the typical members of the Basicurva-gvowp (PI. XV figs. 5, G ; 

 PI. XVIII. fig. 5). But it is so slight as to be hardly recognisable except by a trained 

 eye, and the same may be said of the lateral flattening of the lower brachials. In fact this 

 variety of Antedon midtispina is a good connecting link between the Basicurva- and 

 Gramdifera- groups on the one hand, and the ordinary Comatuke with normal rays and 

 unplated ambulacra on the other, for the plating of the disk is very incomplete (PI. L. 

 fig. 4) and the ambulacral skeleton of the pinnules by no means well differentiated. 



There are thirteen arms in this individual, owing to the presence of three distichal 

 series. One of these is only two-jointed, and the first syzygy above it is in the third 

 brachial (PI. L. fig. 3), just as in the case of Antedon anyusticalyx already referred to 

 on p. 241 (PI. L. fig. 1). But of the two arms which follow each tridistichate series one 

 has the normal syzygy (for this type) between the first two brachials, while in the other 



■See pp. 117-119. 



(ZOOL. CHALL. EXP.— PART LX. — 1887.) OoO 32 



