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



internodes, especially as compared with Pentacrinus mulleri, in which the stem reaches 

 about the same length. There are also more arms in Pentacrinus decorus than in Penta- 

 crimis hlahei, in which palmar series are very rarely present, so that tjie total number of 

 arms would not exceed twenty. But the great distinguishing character of Pentacrinus 

 hlahei is the nature of its bifascial articulations and syzygies. Seen from the dorsal side 

 or in profile (PL XXXI. figs. 1, 2 ; PL XXXII. fig. 15), the third radial shows a strong 

 backward projection into the second. But its proximal face not only is concave from 

 side to side, but also slopes strongly downwards and backwards ; and the upper ventral 

 edge of the second radial is bent forward so as to fit into the gap thus formed 

 (PL XXXII. fig. 18). There is a very slight indication of this in Pentacrinus 

 naresiamis (PL XXX. figs. 1, 11, 12) ; but the two species resemble on,e another much 

 more closely in the curious angular form of the syzygial faces. Those of Pentacrinus 

 naresianus (PL XXX. figs. 20, 21, 23) have been alre.ady described, and those of 

 Pentacrinus hlakei are shown in PL XXXII. Whether it be a brachial syzygy 

 (figs. 4, 5, 7) or one in the distichal axillary (figs. 9, 12, 14) the form is just the same. 

 The proximal face of the epizygal rises to a sharp crest, which is interrupted by the 

 central canal, and fits into a corresponding re-entering angle on the distal face of the 

 hypozygal, so that the muscle-plates of its proximal face are bent strongly forwards, 

 just as they are in the bifascial articulation of the second radials with the axillaries 

 (PL XXXII. figs. 15, 18). The general appearance of the syzygies in the side view of 

 an arm is well shown in PL XXXIII. fig. 2, which should be compared with the 

 corresponding figure of Pentacrinus naresianus (PL XXX. fig. 23). The flattened 

 shape of the lower joints is also well shown in the former figure. Judging from the 

 torn fragment of the disk which came away from this arm-base, we may suppose that 

 its anambulacral plating was tolerably well developed. This j)lating extends out on to 

 the arms, covering in the muscular bundles at the sides of the narrow arm-groove, 

 though to a less extent than in the four preceding species. The pinnule-ambulacra 

 (PL XXXIII. fig. 1) are much in the same condition as those of Pentacrinus naresianus 

 (PL XXVII. fig. 11), the covering plates resting upon the toothed edge of a coijtinuous 

 calcareous band which is not perfectly differentiated into side plates. 



8. Pentacrinus decorus, WyviUe Thomson, 1864 (PL XXXIII. figs. 4-6 ; Pis. 

 XXXIV.-XXXVIL; PL LVIL figs. 2-5; PI. LVIIl. figs. 1^3; PL LIX. figs. 1-4; 

 PL LXIL). 



1864. Pentacrinus {Neocrinus) decorus, WyviUe Thomson, The Intellectual Observer, August 1864, p. 7. 



1864. Peiitacrinus decorus, Liitken, Vidensk. Meddel. f. d. nat. Foren. i Kjfibenhavn, 1864, Nr. 13-16, p. 208. 



1865. Pentacrinus {Neocrimis) decorus, Wyville Thomson, Phil. Trans., 1865, vol. civ. p. 542. 

 1869. Pentacrinus Miilleri, Pourtalfes, Bull. Mus. Comp. Zocil., vol. i.. No. 11, p. 357. 



1872. Pentacrimis MiUleri, Wyville Thomson, Proc. Eoy. Soc. Edin., vol. vii. p. 766; and The Depths of the 

 Sea, p. 442. 



