MONOGRAPH OF THE EXISTING CKINOIDS. 105 



Syzygy. (1) An immovable articulation formed exclusively of ligament fibers; in 

 the comatulids the apposed faces are marked with numerous fine 'radiating 

 ridges; externally the syzygy appears as a narrow usually whitish line run- 

 ning across the arm at right angles to the longitudinal axis (see figs. 2, p. 61, 

 6, p. 63, 30, 34, p. 71, and 35, p. 73, and p. 113). 



(2) This term is often used to denote a pair of ossicles united by sy/ygy, 

 that is, a syzygial pah 1 . 



(3) Pourtales has used this word as the equivalent of intersyzygial inter- 

 val, in Minckert's sense; that is, to denote all the brachials between two adja- 

 cent syzygies. 



T. 



Tegrnen or tegmen calycis. See Disk. 



Terminal axillary. In the comasterids, the terminal orachial of an ungrooved arm, 

 when that brachial bears two pinnules instead of one pinnule and another 

 brachial as usual (see fig. 47, p. 81). 



Terminal claw. The conical, sharp pom ted, more or less curved ossicle which forms 

 the termination of a cirrus (see figs. 4, p. 63, 314-318, p. 273, and pp. 276-278). 



Terminal comb. See Comb. 



Terminal pinnules. The pinnules of the extreme arm tip (see figs. 46, 47, p. 81). 



Terminal stem plate. The Dorsocentral. 



TertibracJis (IIIBr). The ossicles composing a division series or an arm arising 

 from a IIBr (distichal) axillary; the palmars. 



TetrabracJis (IVBr). The ossicles composing a division series or an arm arising 

 from a IIIBr (palmar) axillary; the first post-palmars. 



Topmost columnal. See Proximal columnal. 



Transition segment. The segment upon which the transition between the Ion-' T 

 smooth and the shorter spinous (distal) cirrus segments takes place; the transi- 

 tion segment usually resembles the segments preceding in its proximal two- 

 thirds, and the segments succeeding in its distal third: it is commonly darker 

 in color than any of the other cirrus segments (see figs. 4, p. 63, 363-367, p. 297, 

 and pp. 290-292). 



Transverse ridge. (1) On the joint faces of a muscular articulation, the strong 

 ridge crossing the joint face just dorsal to the central canal and separating the. 

 large single dorsal ligament fossa from the paired interarticular ligament 

 fossae; it serves as the fulcrum upon which the motion at the articulation is 

 accommodated (see figs. 9-11, p. 65, 31, 32, p. 71, and 431, p. 349, and p. 114). 

 (2) On the dorsal surface of the cirrus segments, a serrate ridge, some- 

 times more or less crescentic, which traverses the segments at right angles tu 

 the longitudinal axis; it is commonly central or subterminal in position; trans- 

 verse ridges on the cirrus segments are only developed in a few genera (see 

 figs. 345, p. 289, 349, 352, p. 291, and 353, p. 293, and p. 109). 

 Triangular pinnules. See Prismatic pinnules. 



79146 Bull. 8215 8 



