REPORT ON THE CRINOIDEA. 249 



qui forme un grand evasement obeonique ou caliciforme, ce qui domic ^ notre Crinoitde 

 de la ressemblance avec Ic genres fossiles Ajnocrinus et Bourgueticrinus. Cettc extremity 

 n'est done pas autre chose que le sommet de la tige qui s'elargit successivement." Sars 

 considered the summit therefore as an enlarged uppermost stem-joint analogous to the 

 centro-dorsal of the Comatulse. He was unable to resolve it into any component parts 

 by treating it with alkalies ; and it is consequently not surprising that he was led to 

 regard the whole subradial portion of the calyx as composed of but one single i^iece. In 

 fact he was never able to separate this piece from the radials or the radials from one 

 another, the existence of these plates being only indicated on the outside of the calyx by 

 very faint sutural lines, occasionally rendered more distinct by slight furrows. 



It never seems to have struck him, however, that there might be basal plates below 

 the radials which were similarly, but more closely anchylosed ; and he was led to consider 

 the basals as fused, like those of Comatulse, into a kind of rosette. This circular plate 

 (PI. Villa, figs. 6, 7 ; PL X. figs. 1, 4 — hr) "est situee a I'interieur dans I'espace central 

 laisse en dedans de I'anneau forme par I'adhesion des premiers radiales;"^ but Sars was 

 unable to isolate it, owing to its very close adherence to the first radials. 



It has been pointed out that Rhizocrinus was dredged by Pourtales in 1868 before he 

 had heard of its discovery by Sars ; and the condition of his specimens was fortunately 

 such that he was able to describe the calyx as " composed of a cycle of elongated basal 

 (pelvic) pieces, followed by the much shorter first radials (costals) alternating with them. 

 These j)ieces are all so intimately connected with each other that the sutures are seen 

 with difficulty."^ This account seems to have escaped the notice of Sir Wyville Thomson; 

 for in his description of the " Porcupine " Crinoids' he stated that " in Rhizocrinus the basal 

 series of plates of the cup are not distinguishable. They are masked in a closed ring at 

 the top of the stem." He did not, however, entirely accept Sars's view of the composi- 

 tion of the calyx ; for he went on to say that " whether the ring be composed of the 

 fused basals alone, or of an upper stem-joint with the basals within it forming a rosette 

 as in the calyx of Antedon, is a question which can only be solved by a careful tracing 

 of successiye stages of development." The relatively large specimens which were dredged 

 by the "Porcupine" in 862 fathoms ofi" Cape Clear, show the interbasal sutures very 

 clearly ; and though they were referred at the time to Rhizocrinus lofotensis, they really 

 belong to the Caribbean species Rhizocrinus raivsoni, larger specimens of which were 

 obtained by the "Hassler" ofi" Barbados in 1871, and described by Pourtales in 1874. 

 These, like the " Porcupine " specimens and the Gulf Stream variety of Rhizocrinus 

 lofotensis, also showed distinct interbasal sutures. Pourtales was therefore led to 

 dissent from Sars's description of the calyx in this genus, and to repeat more emphatically 

 his own previous statements concerning the existence of long but closely united basals.* 



1 Crinoides vivants, p. 12. ^ Bull. Mus. Comp. Zool, vol. i. p. 129. 



3 Proc. Boy. Soc. Edin., vol. vii., 1872, p. 770. * Mem. Mus. Comp. Zool., No. 8, pp. 28, 29. 



(zOOL. CHALL. EXP. — PART XiXII.- — 1884.) li 32 



