+ THE VOYAGE OF H.M.S. CHALLENGER. 
Pl. XXXII. figs. 1,2; Pl. XX XVII. figs. 5-8, 19,21; PL XXXIX. figs. 3,5, 6; Pl: XLL 
figs../5, 15; Pl. XLV. figs. 3,5, 65. Pl: RLV lies 1-3 2 Pl do figs) 4p 2082 ier kh Wad 
figs. 5-8). 
The external line of separation frequently disappears altogether, or is only traceable 
with great difficulty, and the two joints, primitively separate, become practically fused 
into one (Pl. XLII. fig. 1; Pl. L. fig. 3). I cannot find any mention of this peculiarity 
in the classical memoir of Johannes Miiller," who spoke of the successive unions of 
the stem-joints indifferently as “ Niithe oder Gelenke.” So far as I can make out, it 
was first noticed by Sir Wyville Thomson in Pentacrinus decorus;? and Liitken® 
subsequently described it in more detail in Pentacrinus asteria and Pentacrinus miilleri. 
Quenstedt * also noticed it in the fossil species Pentacrinus scalaris and Pentacrinus 
jurensis. 
An essentially similar mode of union between certain of the arm-joints was spoken 
of by Miiller as a “syzygy,” and described as an immovable sutural union. The name 
syzygy has since been applied to the sutural union of the nodal stem-joints with those 
next below them; and Miiller’s terms “ hypozygal” and “epizygal” for the two arm- 
joints which are united by syzygy (Pl. XII. figs. 7, 10, 18, 21; Pl. XXXa. figs. 9, 10, 12; 
Pl. XXXII. figs. 4, 9, 15, 18) may be conveniently applied in the case of the stem-joints 
also. 
In all the recent Comatulz the apposed faces of the two portions of a syzygial joint 
are marked by a series of slightly elevated ridges with alternating furrows, which radiate 
from the opening of the central canal towards the dorsal margin of the joint. In 
Actinometra typica these ridges are frequently not perfectly continuous; but they are 
broken up into a row of little elevations, squarish or oblong in shape, and arranged with 
their longer axes radiating outwards from~the central canal. On some joints these are 
not very numerous, and as their terminal faces are marked by median vertical lines, they 
have been wrongly described as surfaces effecting a ligamentous articulation of the 
bifascial type, such as will be described immediately.’ 
The radiating arrangement is usually much less marked in the Pentacrinide than in 
the Comatulz, the striation being frequently only visible at the extreme marginal 
portions of the syzygial surfaces (Pl. XII. figs. 7, 10, 18, 21; Pl. XXI. figs. 1d, 2d, 
5a; Pl. XXX. figs. 20, 21) as figured by Miiller in Pentacrinus asteria,’ while in 
some cases it appears to be absent altogether, the apposed faces being perfectly smooth 
1 Ueber den Bau des Pentacrinus caput-Meduse, Abhandl. d. k. Akad. d. Wiss. Berlin, isi3@ 
* Sea Lilies, The Intellectual Observer, No. 31, August 1864, p. 7. 
’ Om Vestindiens Pentacriner, med nogle Bemaerkninger om Pentacriner og Solilier i Almindelighed, Vidensk. 
Meddel. f. d. nat. Foren. 1 Kjgbenhavn, 1864, Nos. 13-16, pp. 198, 199. 
* Petrefactenkunde Deutschlands, Bd. iv., Asteriden und Encriniden, pp. 196, 230, Taf. 98, figs. 2, 3, 107. 
_ 5 See Lovén, Phanogenia, ett hittills okindt slagte af fria Crinoideer, Ofversigt k. Vetensk.-Akad. Forhandl., 
Arg, xxii, No. 9, p. 230, fig. c; and also P. H. Carpenter, The Comatule of the Leyden Museum, Notes from the Leyden 
Museum, vol. iii. pp. 197-199. 5 Op. cit., Taf. ii. fig. 4, 
