78 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Tho plates of the first circlet are usually reduced in number and may be 

 quite absent; those of the second circlet are often reduced in number, and may 

 be highly metamorphosed. 



In tlio ccliinoids the coronal plates are always lai^e and conspicuous, 

 forming a ring of 10 plates about the poriproctal area, 5 small (the oculars, 

 corresponding to the infrabasals) and 5 large (the genitals, corresponding 

 to tho basals). 

 Costal axillary (IBrj).— The first axillary follo\ving tho radial; the primibrachial 

 axillary; by the older authors this was called the radial axillary (see figs. 1, p. 

 60, 3, p. 62, 29, 30, p. 71, and pp. 109, 110). 

 Costal -pinnules (Pc).— Tho pinnules borne by the costals or primibrachs; among 

 the recent comatulids these occur only in the genus Eudiocrinus, where the 

 second costal or primibrach (IBrj) is not an axillary as usual, but bears a 

 pinnule instead of an additional arm (see figs. 83, p. 136, 84, p. 137 andpp. 114, 115). 

 Costah (IBr). — Tho postradial ossicles as far as the first axillary; the ossicles of the 

 first division scries; tlie primibrachs; in all the recent crinoids except Metw- 

 crinus these are two in number, and, except in Eudiocnnus, terminate in an 

 axillar}'; they are not found in the Pcntametrocrinidaj (see figs. 1, p. 60, 3, 

 p. 62, and 29, 30, p. 71, and pp. 109, 110). 



Though similar in appearance, the first division series is not homologous in 

 all typos. 

 Covering plates. — Thin rounded calcareous plates developed along the borders of 

 the ambulacral grooves and capable of being closed do^vn over them; in pre- 

 served specimens they are easily visible wath a hand lens of low power as a 

 series of oval or approximately circular alternating imbricate plates concealing 

 the ambulacra; covering plates are almost invariably associated with side 

 plates (see figs. 7, p. 63, and 55, p. 81). 



Among the comatuUds covering plates are usually rudimentary or absent 

 except in the families Thalassometridse, Charitometridie and Calometridae; 

 they are also lai^e and well developed in certain of tho Holiometrmoe, and in a 

 few of tho Capillastorinae, in the latter occurring wdthout side plates. 

 CreneUse. — Narrow rounded ridges, arranged more or less radially, most fre- 

 quently observed upon tho joint faces of coliunnals and, in the comatulids, 

 upon tho apposed faces of two brachials united by syzygy (see figs. 34, p. 71, 

 and 525, pi. 1, and pp. 208-210). 

 Crenvlate sutures. — Sutures which are evident externally as a wavj- line (see 



figs. 127. p. 197, and 128, p. 199). 

 Croum. — The calyx and arms; a crinoid deprived of its column; this term is not 



applicable to the comatulids. 

 Cryptosynarthry. — A synartliry which has become modified by a general flattening 

 of the joint faces, together with a restriction in the proportionate area occupied 

 by tho ligament fossae, so that the latter appears very small; tyi^ically a crj-pto- 

 synarthiy shows a very nearly plane articular surface upon which tho position 

 of tho central dorsoventral ridge may with difficulty be traced (see fig. 36, p. 75 

 and p. 113). 



