MONOGRAPH OF THE EXISTING CRINOIDS. 

 I. 



87 



Incised dislc. — A disk in which the iaterambulacral areas are greatly reduced in 

 size through the very strong concavity of their free outer borders (see figs. 16, 17, 

 p. 67, and 24, p. 69). 



Inferior margin. — Of the centrodorsal; the margin of the centrodorsal adjacent to 

 the radials; the outer edge of the ventral surface. 



Fig. 61. — DUQKAM ILLUSTRATING THE HOMOLOGOUS ARMS IN TEN, TWENri", AND THIRTY ARMED COMATCUDS; (o) THE POST- 

 RADIAL SERIES OF A TEN-ARMED COMATULID; (6) THE POST-RADUL SERIES OF A TWENTY-ARMED COMATULID; THE O.SSICLES 

 CORRESPONDING TO THOSE SHOWN IN THE PRECEDING FIGURE, NOW INTERNAL, ARE INDICATED BY A HEA^'Y OUTUNE; 

 (C) THE POST^RADLAL SERIES OF A THIRTY-ARMED COMATWUD; THE OSSICLES CORRESPONDDJO TO THOSE IN FIGURE ARE 

 SHOWN BORDERED WITH HEAVY LINES. 



Infrabasals (IBB). — Small plates forming a circlet below or within the basals and 

 alternating in position with them; in the comatulids they arc not always devel- 

 oped, and if present fuse with the centrodorsal in early life. 



The infrabasals are the equivalent of the oculars in the echinoids (see 

 figs. 565-572, pi. 7, and pp. 313-316). 



Infrarwdal. — The columnal immediately below a nodal. 



Infraradials. — See Suhradials. 



Interambulacral. — Situated %vithin the areas delimited by the ambulacral furrows 

 on the disk. 



