310 THE VOYAGE OF H.M.S. CHALLENGER. 
than in Pentacrinus asterius. There are fewer joints between the successive axillaries, 
and the characters of the pinnules are altogether different. In these latter points Penta- 
crinus miilleri closely resembles Pentacrinus maclearanus (Pl. XVL.), Pentacrinus 
wyville-thomsoni (Pl. XVIII. fig. 1), and Pentacrinus alternicirrus (Pl. XXV.). But 
the first named has only one or two internodal joints in the stem, while Pentacrinus 
wyville-thomsoni has from thirty to forty-five, so that they are both readily distinguish- 
able from Pentacrinus miilleri; while the grouping of the cirri on the stem of 
Pentacrinus altermcirrus is sufficient to distinguish this species at once. 
So far as I can judge from the material at my disposal, Pentacrinus miilleri is 
certainly the most variable of the Pentacrinide with the exception of Pentacrinus 
decorus. The stem does not seem to reach the length which it attains both in the latter 
species and in Pentacrinus asterius. In one instance it is rounded off at the twelfth node, 
only 135 mm. from the calyx, and Rhizopods are attached to the under surface of the 
lowest nodal joint. Another stem tapers gradually downwards from a width of 5 mm. at 
the calyx to 3 mm. at the sixteenth node, where it is rounded off 185 mm. from the calyx. 
The length of the internodes varies a good deal in different individuals, though as a 
rule it is tolerably constant in any given stem. The component joints are usually thick 
and thin alternately. This is very marked in the specimen represented in Pl. XIV., 
though not well shown in the figure; while in other cases the joints are more equal in 
height, as shown in Pl. XV. fig. 4. This figure should be compared with the correspond- 
ing one of Pentacrinus asterius (Pl. XIII. fig. 8), in which the cirrus-sockets are not so 
deeply hollowed as they are in Pentacrinus miilleri. Their shape, too, is somewhat 
variable in the latter type. In some stems (Pl. XV. fig. 4) they are transversely oval as 
in Pentacrinus asterius (Pl. XIII. figs. 4, 8), though not reaching so near the top of the 
nodal joint. But they always extend slightly downwards on to the hypozygal, which is 
not the case in that species. In other examples, however, the hypozygal is deeply 
grooved to receive the bases of the cirri, and the sockets thus become more circular in 
form ; so that it appears as if the cirri were borne conjointly by the two syzygial joints. 
This has been described as an important difference between Pentacrinus miilleri and 
Pentacrinus asterius, but erroneously so; for the whole of the articular surface is always 
on the nodal joint, which is the only one pierced by the canals lodging the cirrus-vessels. 
The cirri, though always stout, are considerably shorter in some forms than they are 
in others; and while some of them have quite smooth terminal joints, those of other 
individuals bear small blunt processes which never, however, reach to the size of a spine. 
The “Blake” collection includes a curious fragment of a stem which had broken 
between a nodal joint and the first joint of the internode above it. The upper part of 
_ the stem and the calyx are missing; but six irregularly shaped joints have been added 
above the node. One would like to know whether this reparation would ever have 
resulted in the formation of a new calyx and arms. Such an extensive reparation 
