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



than in Pentacrinus asterius. Thei-e are fewer joints between the successive axillaries, 

 and the characters of the pinnules are altogether different. In these latter points Penta- 

 crinus miilleTi closely resembles Pentacrinus macleaixmus (PI. XVI.), Pentacrinus 

 wyviUe-thomsoni (PI. XVIII. fig. l), and Pentacrinus alternicirrus (PI. 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- 

 al)le from Pentacrinus mulleri ; while the grouping of the cirri on the stem of 

 Pentacrinus alternicirrus is sufficient to distinguish this species at once. 



So far as I can judge from the material at my disposal, Pentacrinus mulleri is 

 certainly the most variable of the Pentacrinidje with the exception of Pentacrimts 

 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 ofi" at the twelfth node, 

 only 135 mm. from the calyx, and Rhizopocls 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 ofi" 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 mulleri. 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 hj-pozygal, 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 difi"erence between Pentacrinus mulleri and 

 Pentacrinus asterius, but erroneously so ; for the whole of the articular surface is always 

 on the nodal joint, which is the oul}- 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 Avliile 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 joiut 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 



