74 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Calyx plates. — The plalcs primarily enclosing llic visceral mass; these include (1) 

 the infrabasals (when present), (2) the basals, (3) the radials, and (4) the 

 orals. 



Carinate cirri. — Cirri in which median longitudinal keels are developed on the dorsal 

 side of each of the outer segments (see fig. 344, p. 287, and pp. 285-286). 



Central anus. — An anus situated in the center of the disk (see figs. 21, 25-28, 

 p. 69, and pp. 110-111). 



Central canal. — A continuous canal running through all the brachials and lodging 

 the axial cord, which latter is the radial extension of the so-called dorsal nervous 

 system. It ])asscs tlirough the bracliials just ventral to the center of the 

 transverse ridges of the articular faces (see figs. 9-11, p. 65, 31-34, p. 71, 

 and 431, 432, p. 349, and p. 114). 



Central cavity.— Oi the centrodorsal, the interior cavity in which is lodged the 

 chambered organ and accessory structures (see figs. 13, p. 65, 229, 232-234, 

 p. 247, 235-242, p. 249, 243-249, p. 251, 250-255, p. 253, 256-261, p. 255, 262- 

 266, p. 257, 267-273, p. 259,274-279, p. 260, 280-285, p. 261, 286-291, p. 262, 

 292-297, p. 263, 298, 299, 302, p. 264, and 592, 593, pi. 15, and pp. 232-234). 



Central mouth. — A mouth is said to be central when it occupies the exact center 

 of the ventral surface of the disk, and all the disk ambulacra are of the same 

 length. In reality the mouth is never quite central (see figs. 20, 22-24, p. 69, 

 117, p. 183, and pp. 110-111). 



Central plate. — See Centrale. 



Central plug. — The more or less spongy calcareous deposit found on the ventral sur- 

 face of the radial pentagon; it may be so slightly developed as barely to con- 

 ceal the rosette, or it may fill the entire area between the outer borders of 

 the muscular fossae of the articular faces of the radials. In general the central 

 plug is well developed in the oligophreate species, but absent or at most 

 slightly developed in the macrophreate species (see figs. 11, p. 65, 441, 442, 

 p. 351, and pp. 373-374). 



Centrale. — The dorsal apical plate in the genera Marsupites and Uintacrinu.s. It 

 is the morphological equivalent of the centrodorsal of the comatulids, plus 

 the larval stem (see figs. 565, 572, pi. 7, and pp. 240-242). 



Centrodorsal. — In the comatulids tlie plate occupying the center of the aboral (dorsal) 

 surface; it is usually large, discoidal, hemispherical or more or less conical, 

 and bears numerous cirri on its edges, though never in its center; in certain 

 of the Comasterida; it may be reduced to a thin noncirriferous stellate plate 

 occupj'ing the central space in tlie dorsal surface of the radial pentagon (see 

 figs. 1, p. 60, 10, 14, p. 65, 29-30, p. 71, and 191-198, p. 237, and pp. 219-220). 

 Ontogenetically the centrodorsal is the topmost columnar of the larval stem, 

 plus the circlet of infrabasals in those species in which infrabasals are devel- 

 oped. It is the osteological equivalent of a suiglo cirriferous nodal as seen in 

 the p"ntacrinites, though within it is compressed the equivalent of the entire 

 pentacrinite column. 



