REPORT ON THE CRINOIDEA. 15 



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 Pentacrinidse has long been familiar 

 to palaeontologists. 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 LorioP ; 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 

 Pentacrinidae. There may be only one or two as in Pentacrinus madearanus 

 (PL XVI.) ; or the number may reach forty-five, as in the lowest parts of the stem of 

 Pentacnniis wyville-thomsoni (PL XIX. fig. 1), or any lesser figure (Pis. XL, XIV., 

 XXVIIL, XXXIV.-XXXVL, XXXVIIL, XL., XLIL, XLIV., XLV., XLVIIL-LIII.) 

 These internodal joints are sometimes smooth externally (PL XL ; PL XIII. fig. 8 ; PL XIX. 

 figs. 1-5 ; PL XXVII. fig. 1 ; PL XXVIIL fig. 2 ; PL XXXa. fig. 6 ; PL XXXI. fig. 3 ; 

 PL XXXV. fig. 2; PL XLL figs. 5, 15; PL XLIL-XLIV. ; PL XLVII. fig. 6); or 

 they may be more or less ornamented with ridges and tubercles (PL XIII. fig. 7 ; 

 PL XXXV. fig. 1 ; PL XXXVI. ; PL XXXVIIL; PL XXXIX. figs. 3, 8-11 ; PL XL. ; 

 PL XLL fig. 1; PL XLV. figs. 1, G ; PL XLVIL figs. 1, 2 ; PL LI. fig. 8; PL Lll. fig. 2; 

 PL LIIL figs. 2, 4-6). The young joints formed at the top of the stem are steUate or 

 nearly pentagonal (PL XIIL fig. 9; PL XXII. figs. 1-12; PL XXIII; PL XXVI. 

 fig. 18 ; PL XXXIV. fig. 9 ; PL XXXVII. figs. 13-16), so that the upper part of the stem 

 is marked by five more or less prominent interradial ridges (PL XL ; PL XIIL fig. 1 ; 

 PL XV. figs. 1, 2 ; PL XVIII. figs. 1, 2 ; PL XIX. figs. 1, 6, 7 ; PL XXXI. ; Pis. XXXV.- 

 XXXVII. ; PL XXXIX. fig. 1 ; PL XLIIL). In some species {oi Metaainus especially) 

 this condition is retained throughout the whole length of the stem (PL XXXVIIL ; 

 PL XXXIX. figs. 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 XL ; PI XIIL fig. 11 ; PL XIX. figs. 1, 4, 5 ; PL XXII. figs. 13, 14, 

 23-26 ; PL XXVIIL fig. 2 ; PL XXX. figs. 25-30 ; PL XXXVI. ; PL XLL figs. 3, 7 ; 

 PL XLA'II. 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, Wi. 



- Monographie des Crinoides fossilesde la Suisse, Mifm. Soc. Pal. Suisse, 1877-79, pp. 122, 144. 



