at 
REPORT ON THE ORINOIDEA. 1d 
the re-entering angles of the former being deeper than those of an ordinary internodal 
joint. (Compare Pl. XXXIX. figs. 8,9; Pl. LIIL. figs, 2, 4). 
The occurrence of syzygies in the stem of the Pentacrinide has long been familiar 
to paleontologists, This is due to the fact that the stem breaks most easily at these 
points, so that stem fragments are not uncommon in the fossil state with syzygial faces 
at one or both ends. This has been noticed both by Quenstedt! and by de Loriol?’ ; but 
these fragments have sometimes been figured in an inverted position, the syzygy being 
represented as at the upper surface of the nodal joint, whereas it is naturally at the 
under surface. 
Within each nodal joint the vascular axis of the stem expands into a miniature 
edition of the chambered organ in the calyx (Pl. XXIV. figs, 3, 4,ch.n.); and from each 
chamber is given off one cirrus-vessel (fig. 4,cv). This is sheathed in a very delicate 
extension of the fibrillar envelope of the vascular axis (ca), and passes outwards into the 
central canal of the cirrus. 
The number of internodal joints varies very considerably in the different species of 
Pentacrinide. There may be only one or two as in Pentacrinus maclearanus 
(Pl. XVI); or the number may reach forty-five, as in the lowest parts of the stem of 
Pentacrinus wyville-thomsoni (Pl. XIX. fig. 1), or any lesser figure (PIs;201 7 XenVes 
DOCV ITE XIV XX RV XXXVI XI, XLII; XLIV., XLV. XLVIII.-LIIL.) 
These internodal joints are sometimes smooth externally (Pl. XI. ; Pl. XIII. fis. 8; Pl. XTX. 
figs. 1-5; Pl. XXVIL fig. 1; Pl. XXVIII. fig. 2; Pl. XXXa. fic. 6; Pl. XXXI. fig. 3; 
Pl XXXY. fig. 2; Pl. XLI figs. 5, 15; Pl. XLIL-XLIV.; Pl. XLVIL fig. 6); or 
they may be more or less ornamented with ridges and tubercles (Pl. XIII. oe Ts 
EAS ORY rigs Eh XR XVI Pl) XX RVI; Pl XXXIX. fips, 8) 8-11 + PIX 
Pl. XLI. fig. 1; Pl. XLV. figs. 1, 6; Pl. XLVII. figs. 1,2; Pl. LL fig. 8; Pl. LIL fig: 2: 
Pl. LIL. figs. 2, 4-6). The young joints formed at the top of the stem are stellate or 
nearly pentagonal (Pl. XIII. fig. 9; Pl. XXII. figs. 1-12; Pl. XXIII; Pl. XXVL 
Bowtie Pe XX REV fie.9: Pl XXX VIL figs. 13-16), so that the upper part of the stem 
is marked by five more or less prominent interradial ridges (PI. XI.; Pl. XIII. fies als 
OGY figs: 12's XVINE fies! 1, 2: Pl. XTX! fies 1, 6,7; PUXXXT > Pls. XXXV— 
XXXVIT.; Pl. XXXIX. fig. 1; Pl. XLII). In some species (of Metacrinus especially) 
this condition is retained throughout the whole length of the stem (Pl. XXXVIIL; 
BIOECXEX. fies. 3-11; Pl. XL; Pl) XLIX, figs. 1-3); but in others the joints gradually 
become more rounded, or at any rate pentagonal, as new ones are formed successively 
above them (Pl. XI.; Pl XIII. fig. 11; Pl. XIX. fase 154,55) Pl. XXII. fies: Tone 
23-26; Pl. XXVIII. fig. 2; Pl. XXX. figs. 25-30; Pl. XXXVI.; Pl. XLI. figs. 3, 7; 
Pl. XLVIL figs. 4, 8). A continual production of new joints goes on at the top of 
1 Encriniden, pp. 196, 230, Tab. 98, figs. 2, 3, 107. 
* Monographie des Crinoides fossiles de la Suisse, Mém. Soc. Pal, Swisse, 1877-79, pp. 122, 144. 
