CRIXOIDEA. 



411 



The dorsal or aboral integument is hardened in Antedon by the 

 formation within it of a system of calcareous plates, which collec- 

 tively constitute the " cup " or " calyx," and which in large part 

 correspond with the " apical disc " of the Echinoids. The central 

 piece of the calyx is known as the " centrodorsal " plate (fig. 285, cd\ 

 and is developed from the topmost joint of the stem in the young 

 Feather-star. It carries the cirri, and has soldered on to it five 

 "radial" plates (fig. 285, r), which represent the "ocular plates" of 

 the Echinoids. There are thus apparently no representatives of the 

 " genital plates " of the Echinoids. In the great majority of the 

 recent Feather-stars, however, these plates are really present, though 

 they exist only in a metamorphosed condition. They are, in fact, 

 fused together to form a so-called " rosette-plate," which is con- 

 cealed from view externally, and lies hidden between the centro- 

 dorsal and radial plates. This " rosette-plate " consists, therefore, 

 of the amalgamated interradial plates which are known as the 

 " basals " in the stalked Crinoids. Following the first cycle of 



cm 



Fig. 286.— a, Ventral or actinal surface of the body of ComaUda (Antedon) rosacea^ enlarged, 

 showing the central mouth (o), the excentric, proboscidiform anus (an), and the brachial grooves 

 (ag), continued from the bases of the arms across the disc to the mouth, b, Side-view of the lower 

 part of Antedon Icevis, showing the calyx, the bases of the arms (b), and the roots of the dorsal 

 cirri, a single cirrus (c) being left complete, enlarged. (After P. Herbert Carpenter.) 



"radials" in Antedon are two other circles of radial plates (the 

 " second radials " and " axillary . radials "), the outermost circle 

 carrying the bases of the jointed arms (fig. 285, sr and ar). 



The upper or ventral surface of the body is covered with an 

 imperfectly calcified, coriaceous skin, and carries the aperture of the 

 mouth. In Comatula rosacea the mouth is central (fig. 286, a, 0), 



