304 THE VOYAGE OF H.M.S. CHALLENGER. 
figure of that type. But it corresponds in every respect with the two individuals in the 
national collection which Sir Wyville himself described in 1864 as Pentacrinus 
(Neocrinus) decorus. A large number of examples, obviously of the same type, were 
dredged by the “ Blake”; and I have no hesitation in considering Pentacrinus decorus 
as a good species; though for reasons given above I do not regard it as a type of 
subgeneric value. In fact Sir Wyville himself seems to have recognised this sub- 
sequently ; for while still confounding Pentacrinus decorus with Pentacrinus miilleri, 
he dropped the names Cenocrinus and Neocrinus altogether, and simply spoke of 
Pentacrinus asterius and Pentacrinus miilleri. 
Pentacrinus decorus differs from Pentacrinus blaket and Pentacrinus naresianus 
in the flatness of the syzygial faces on the arm-joints (Pl. XXXVIL. figs. 3, 4), both 
these species having strongly angular syzygial faces (Pl. XXXa. figs. 9, 10; Pl. XXXII. 
figs. 4, 5, 7, 9, 12, 14). Pentacrinus naresianus has only ten arms, while the primary 
ams of Pentacrinus decorus, like those of Pentacrinus blakei, may divide once or 
twice. The second division is, however, more common in Pentacrinus decorus than in 
Pentacrinus blakei, in which palmar series are rare (Pl. XXXL); though distichals 
generally occur with considerable regularity all round the cup, which is by no means 
always the case in Pentacrinus decorus (Pls. XXXV., XXXVI). The general 
characters of the pinnules and of their ambulacral plating are much the same in the 
two species; but the two sets of ambulacral plates are on the whole much _ better 
differentiated in Pentacrinus blakei than in Pentacrinus decorus (Pl. XXXIIL fig. 1; 
Pl. XXXVII. figs. 23, 24). In the latter species (PI. XXXIII. fig. 4) the arm-groove 
itself'is more completely covered in by the bases of the pinnule-ambulacra, which over- 
lap one another alternately from opposite sides much more perfectly than in Pentacrinus 
blakec (Pl. XXXIIT. fig. 3). But the perisome covering the muscular bundles in the 
intervals between the ventral edges of the arm-joints is not plated in Pentacrinus 
decorus (Pl. XXXII. figs. 4, 6) as itis in Pentacrinus blakei (fig. 3), and also in some 
other Pentacrini previously described, together with some species of Metacrinus. But 
the chief and most obvious difference between Pentacrinus decorus and Pentacrinus 
blaket, apart from the peculiarities of the brachial syzygies in the latter species, lies in 
the characters of the stem. The internodes in most stems of Pentacrinus decorus are 
considerably longer than those of Pentacrinus blakei, as is evident upon comparison of 
Pls. XXXIV. and XXXVII. with Pl. XXXL; and the nodal joints are markedly different 
in the two species. Those of Pentacrinus decorus are considerably enlarged above the 
deeply hollowed cirrus-sockets (Pl. XXXVI.), so that the outline of the stem is not 
uniform as it is in Pentacrinus blake: (Pl. XXXI. fig. 3); while the contour of the 
nodal joints as seen from beneath is less rounded in Pentacrinus decorus (Pl. XXXVII. 
fig. 21) than in Pentacrinus blakei (Pl. XXXII. fig. 1). "The general appearance of 
5 
the infra-nodal joints (Pl. XXXIL fig. 2; Pl. XXXVIL fig. 19) and also of the ordinary 
