MONOGRAPH OF THE EXISTING CRINOIDS. 

 7. 



87 



Incised disk. A disk in which the interambulacral 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. DIAGRAM ILLUSTRATING THE HOMOLOGOUS ARMS IN TEN, TWENTY, AND THIRTY ARMED COMATUUDS; (a) THE POST- 



RADLIL SERIES OF A TEN-ARMED COMATULID; (6) THE POST-RADIAL SERIES OF A TWENTY-ARMED COMATUUD; THE OSSICLES 

 CORRESPONDING TO THOSE SHOWN IN THE PRECEDING FIGURE, NOW INTERNAL, ARE INDICATED BY A HEAVY OUTLINE; 

 (C) THE POST-RADIAL SERIES OF A THIRTY-ARMED COMATULID; THE OSSICLES CORRESPONDING TO THOSE IN FIGURE a ARE 

 SHOWN BORDERED WITH HEAVY LINES. 



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

 alternating in position with them; hi the comatulids they are 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). 



Infra/nodal. The columnal immediately below a nodal. 



Infraradials. See Subradials. 



Interambulacral. Situated within the areas delimited by the ambulacral furrows 

 on the disk. 



