334 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) decorvs. A large number of examples, obviously of the same iyjie, 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 millleri, 

 he dropped the names Cenocrinus and Neocrinus altogether, and simply spoke of 

 Pentacrinus asterius and Pentacrinus millleri. 



Pentacrinus decorus differs from Pentacrinus hlakei and Pentctcrinus naresianus 

 in the flatness of the syzygial faces on the arm-joints (PL XXXVII. 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 

 arms of Pentacrinus decorus, like those of Pentacrinus hlahei, may divide once or 

 twice. The second di^^sion is, however, more common in Pentacrinus decorus than in 

 Pentacrinus blaJcei, in which palmar series are rare (PL XXXI.) ; though distichals 

 generally occur wdth considerable regularity aU round the cup, which is by no means 

 always the case in Pentacrinus decorus (Pis. XXXV., XXXVI. ). The general 

 characters of the pimiules and of their ambvdacral plating are much the same in the 

 two species ; but the two sets of ambulacral plates are on the whole much better 

 difterentiated in Pentacrinus hlakei than in Pentacrinus decorus (PL XXXIII. fig. 1 ; 

 PL XXXVII. figs. 23, 24). In the latter species (PL 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 

 hlakei (PL XXXIII. 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 XXXIII. figs. 4, 6) as it is in Pentacrinus hlakei (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 

 hlakei, 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 hlakei, as is evident upon comparison of 

 Pis. XXXIV. and XXXVII. with PL XXXI. ; and the nodal joints are luarkedly difi'erent 

 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 hlakei (PL XXXI. fig. 3); while the contour of the 

 nodal joints as seen from beneath is less rounded in Pentacrimis decorus (PL XXXVII. 

 fig. 21) than in Pentacrimis hlakei (PL XXXII. fig. 1). The general aj^pearauce of 

 the infra-nodal joints (PL XXXII. fig. 2 ; PL XXXVII. fig. 19) and also of the ordinary 



