104 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



SubracliaLs do not occm- in the adults of any of the recent species, but 

 the right posterior subradial, or raiUanal, is a lai^e and coixspicuous plate in 

 all [H'ntacrlnoid lan'a\ 



De Koninck used the term subradial as the equivalent of basal, but in 

 this use he has not been followed by subsequent authors. 



Supplementarij I'lgament fossx. — Triiiii<;ular ligament fossse developed on the outer 

 ends of the transverse ridge (sco fig. 432, p. 349). 



Supplementary muscle plates. — Thin plates developed in the proximal inner angle 

 of the muscular fossa?, and lyijig upcm the muscular fossae; their function and 

 significanco are not understood, but their outer margm may mark the limit of a 

 growth stage characterized by thick muscle plates, short muscle fibers, and a 

 less flexible articulation than that of the adult, or they niay be developed as a 

 result of the partial deterioration and shortening of the inner fibers of the 

 muscle bundles (see fig. 431, p. 349). 



Supranodal. — The columnal immediately above a nodal (see fig. 127, p. 197). 



Supra-palmars. — Sec Post-palrnars. 



Suture. — A union of two adjacent ossicles formed of amorphous connective tissue 

 strands; sutures are of two kinds: 



(1) Loose suture. — A suture in which the connecting strands of connective 

 tissue arc entirely devoid of any calcareous deposit, allowing of a certain 

 amount of play between tlie plates. 



(2) Close suture. — A suture m which there has been more or less of a deposit 

 of calcareous matter on the apposed edges of the plates so that, though not 

 welded together, they are unmovably united. 



Symmetry. — Three types of symmetry, occur in the comatulids, as follows: 



(1) Bilateral symmetry, in the free swimming larvae. 



(2) Pcutamerous symmetry, in the adults of most of the species; this 

 pcntamerous symmetry is never quite perfect, the digestive system, for instance, 

 never bemg afifected by it (see figs. 22-24, p. 69, 77, p. 130, 78, p. 131, 80, 

 p. 133, 101, p. 163, 107, p. 173, and pp. 152-161). 



(3) Secondary l)ilatcral symmetry, in the adults of certain species of the 

 family Comasteridae (see figs. 26-28, p. 69, 45, p. 79, and pp. 110-111); (see 

 Axis and Orientation). 



Synarthrial tubercles. — Dorsal external tubercles developed on the line of union 

 between two ossicles joined by synarthry (see figs. 86, p. 141, 110, p. 176, 

 112, p. 179). 



Synarthry. — Sec Articulations Ba. 



Synostosis. — A complete welding of two adjacent plates through the medium vi cal- 

 careous interdcpositi(m. 



Syzygial pair. — A pair of brachials, or of any other ossicles, united by syzygy (see 

 fig. 35, p. 73, and p. 113). 



Syzygium. — See Syzygy. 



