80 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The cryptosynarthry is a synarthrial articulation which has lost all power 

 of motion and become immovably fixed, so that it appears externally exactly 

 like a syzygy, with which it has usually been confused. A parallel develop- 

 ment from the synarthry is the pseudosyzygy; both these types of articulation 

 sometimes occur in the same species. 



Cystid stage. The stage in tne development of the young comatulid when the 

 calyx is composed only of basals and orals; the prebrachial stage (see figs. 

 407, 410, p. 317, 532, pi. 3, and 542, 544, 547, pi. 4). 



D. 



Defective interpolated arm division. Arm division in which the IIIBr and further 

 division series are 3 (2 + 3) instead of the usual 4 (3 + 4), as in Capillaster and 

 Nemaster. 



Deltoids. See Orals. 



Dermal plates. Plates arising from a center of ossification within the dermal layers; 

 secondary plates; these plates are more or less circular, and are not fenestrated, 

 being built up of concentric calcareous deposits (see fig. 18, p. 67, and p. 195). 



Dice-box sfiaped. Hourglass shaped; differing from cylindrical in that the sides 

 are, from all points of view, concave instead of parallel (see figs. 141, 142, p. 205, 

 396, p. 309). 



Disk. (1) The integument covering the ventral surface of the body proper (that is, 

 considered without the arms), between the arm bases; it is traversed by the 

 ambulacral grooves which converge at the mouth, and in one of the areas delimit- 

 ed by these grooves it rises into the anal tube (see figs. 15-19, p. 67, 117, p. 183, 

 and p. 110). 



(2) The visceral mass which rests on the calvx and arm bases (see fig 89, 

 p. 147). 



Disk ambulacra. The ambulacra which traverse the disk, as contrasted with the 

 ambulacra on the arms and pinnules (see figs. 15-19, p. 67, 117, p. 183, and 

 p. 110). 



Distal. In the comatulids distance is reckoned in either direction (dorsal or ven- 

 tral) from the suture between the centrodorsal and the radials; of two points 

 on the arms, centrodorsal or column, the one which is further from this suture 

 is said to be the more Distal, while the one which is nearer to this suture is 

 said to be more Proximal. See Dorsal Surface, Upper Surface, Ventral Surface, 

 etc. (see fig. 1, p. 60). 



Distal cirrals. The comparatively short outer cirrus segments which bear dorsal 

 processes; this term is used in contrast to Proximal cirrals. 



Distal pinnules. The pinnules beyond those which bear the genital glands (see fig. 

 l,p. 60, and pp. 112-113). 



Distichal pinnule (P D ). The pinnule or pinnules borne by the IIBr series (secun- 

 dibrachs or distichals) ; these are never present unless the elements of the IIBr 

 series are four or more in number, except in Uintacrinus where the IIBr 2 (sec- 

 ond secundibrach or distichal) bears a pinnule instead of an additional arm 

 (see figs. 81, p. 134, and 82, p. 135, and p. 112). 



