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



ino- from Millericrinus in the verticillate arrangement of the cirri, and in having very 

 small basals, which do not meet externally. Thus he says " pieces basales fort petites, en 

 general arrondies, non contigues et reposant sur les cinq angles de la tige." On the other 

 hand, Cainocrinus has a complete ring of basals like Millericrinus, but a stem with 

 verticils of cirri like Pentacrinus. I cannot, however, regard this classification as 

 satisfactory ; for even in those species of Pentacrinus which have an incomplete basal 

 ring there is a great amount of variation in the extent to which the central ends of the 

 basals are joined, and in the size of their outer ends which appear between the radials and 

 the top stem-joint (PL XL; PL XII. fig. 16; PL XIII. fig. 1; PL XIV; PL XV. 

 figs. 1,2; Pis. XXVIIL, XXIX. ; PL XXX. figs. 1,4; PL XXXI. figs. 1, 2 ; PL XXXIV. 

 figs. 1,8; Pis. XXXV., XXXVI. ; PL XXXVII. figs. 1,2). I have elsewhere stated my 

 reasons for not adopting Cainocrinus ae, a genus distinct from Pe7itacrinus ;^ and the 

 results of my examination of the large series of Pentacrinidse dredged by tlie Challenger 

 and the " Blake " Expeditions has only served to strengthen my opinion. It must be 

 remembered that the question of the more or less perfect closure of the basal ring simply 

 has reference to its appearance on the exterior of the calj^x. The inner ends of the basals 

 always meet one another around the neurovascular axis. But they are sometimes not in 

 contact by the whole length of their sides, so that their outer ends appear to be separated 

 by the radials (compare PL XII. figs. 1, 2, 16 ; PL XIII. fig. 1 ; PL XIX. figs. 6, 7; 

 PL XX. figs. 1-3; PL XXVI. fig. 11 ; PL XXX. figs. 1, 4 ; PL XXXIV. figs. 1, 8 ; 

 PL XXXVI. ). 



The closure of the basal ring, therefore, is so extremely variable within specific 

 limits that it scarcely afi"ords characters of specific, much less of generic value. 



So far as the fossil species are concerned, however, it is quite possible that the more 

 or less perfect closure of the basal ring on the exterior of the calyx may afi'ord characters 

 of some systematic value. But I strongly suspect that the examination of a large series 

 of specimens would indicate a very great variability in the size of the basals, just as in 

 the recent types. 



The unique specimen o? Pentacrinus maclearanus (PL XVI.) has a closed basal ring, 

 and would therefore be called a Cainocrinus by de Loriol. In Pentacrinus wyville- 

 thomsoni there is sometimes a very close union between the pentagonal basals as in 

 PL XIX. figs. 6, 7, and PL XX. figs. 1-3 ; while in other specimens the basals are more 

 triangular in shape and less closely united, as is shown, with a little exaggeration, in 

 PL XVIII. figs. 1,2. It occasionally happens that one or two of the basals fail to meet 

 their fellows, but the ring is always more or less complete. 



Variations of a similar kind, though greater in degree, are presented by Pentacrinus 

 alternicirrus. Some individuals have prominent, rhomboidal basals not meeting laterally, 

 like those of Pentacrinus asterius (PL XIII. fig. 1 ) ; while in others they are much less 



^ Jonrn. Linn. Soc. Land. (Zool.), vol. xv. p. 210; and Bull. Mm. Comp. ZooL, vol. x., No. 4, p. 168. 



