282 THE VOYAGE OF H.M.S. CHALLENGER, 
ing 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 
général arrondies, non contigués 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-joimt (PL XI.; Pl XII. fig. 16; Pl XIIL fig. 1; Pl OVE exXave 
figs. 1,2; Pls. XXVIII, XXIX.; Pl. XXX. figs. 1,4; Pl. XXXI figs. 1,2; Pl. XXXIV. 
figs. 1,8; Pls. XXXV., XXXVI. ; Pl. XXXVIL. figs. 1,2). I have elsewhere stated my 
reasons for not adopting Cainocrinus as a genus distinct from Pentacrinus ;' and the 
results of my examination of the large series of Pentacrinidee dredged by the 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 calyx. 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. fie; Ws Ply ROR ese eas 
PIOKX. figs: 123; PL XXXVI. fig, 1; Pl) Xe figs) 4s Pl REVS fear si 
PL XXXVI). 
The closure of the basal ring, therefore, is so extremely variable within specific 
limits that it scarcely affords 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 afford 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 of Pentacrinus maclearanus (P\. XVI.) has a closed basal ring, 
and would therefore be called a Cainocrinus by de Loriol. In Pentacrinus wyville- 
thomson 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 im others they are much less 
1 Journ. Linn. Soc. Lond. (Zool.), vol. xv. p. 210; and Bull. Mus. Comp. Zodl., vol. x., No. 4, p. 168. 
