330 THE VOYAGE OF H.M.S. CHALLENGER. 
internodes, especially as compared with Pentacrinus miilleri, in which the stem reaches 
about the same length. There are also more arms in Pentacrinus decorus than in Penta- 
crinus blakei, in which palmar series are very rarely present, so that the total number of 
arms would not exceed twenty. But the great distinguishing character of Pentacrinus 
blake: 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 
naresianus (Pl. XXX. figs. 1, 11, 12); but the two species resemble one 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 already described, and those of 
Pentacrinus blakei 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 avxillaries 
(PI. 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 plating 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 pimnule-ambulacra 
(Pl. XXXII. fig. 1) are much in the same condition as those of Pentacrinus naresianus 
(Pl. XXVIL. fig. 11), the covering plates resting upon the toothed edge of a continuous 
ealeareous band which is not perfectly differentiated into side plates. 
8. Pentacrinus decorus, Wyville Thomson, 1864 (Pl. XXXIII. figs. 4-6; Pls. 
XXXIV.—XXXVII.; Pl. LVI. figs. 2-5; Pl. LVIIL figs. 1-3; Pl. LIX. figs. 1-4; 
Pl. LXII.). 
1864. Pentacrinus (Neocrinus) decorus, Wyville Thomson, The Intellectual Observer, August 1864, p. 7. 
1864. Pentacrinus decorus, Liitken, Vidensk. Meddel. f. d. nat. Foren, i Kjébenhavn, 1864, Nr. 13-16, p. 208. 
1865. Pentacrinus (Neocrinus) decorus, Wyville Thomson, Phil. Trans., 1865, vol. clv. p. 542. 
1869. Pentacrinus Miilleri, Pourtalés, Bull. Mus. Comp. Zodl., vol. i., No. 11, p. 357. 
1872. Pentacrinus Miilleri, Wyville Thomson, Proc. Roy. Soc. Edin., vol. vii. p. 766; and The Depths of the 
Sea, p. 442. 
