104 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Subraclials do not occur in the adults of any of the recent species, but 

 the right posterior subradial, or radianal, is a large and conspicuous plate in 

 all pentacrinoid larvse. 



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

 this use he has not been followed by subsequent authors. 



Supplementary ligament fossse. Triangular ligament fossae developed on the outer 

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



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

 of the muscular fossas, and lying upon the muscular fossse; their function and 

 significance are not understood, but their outer margin 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 may 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-palmar s. See Post-palmars. 



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 are entirely devoid of any calcareous deposit, allowing of a certain 

 amount of play between the plates. 



(2) Close suture. A suture in 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 immovably united. 



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



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



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

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

 never being affected 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 bilateral symmetry, in the adults of certain species of the 

 family Comasteridse (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. See Articulations Bo.. 



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

 careous interdeposition. 



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. 



