90 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Interprimibrachial areas. The areas in the lateral perisome of the visceral mass 

 between the elements of the primibrachial (IBr) series. 



Interradial. Occupying a position between any two of the five radii, which are 

 determined by lines drawn from the center of the animal along the center of 

 the radials and of the ossicles of the IBr scries, and thence continued outward. 



Interradial mouth. In certain of the Comasteridae the mouth moves from its original 

 position at the. base of the anterior ray and comes to lie near the margin of the 

 disk midway between the bases of the anterior and the right anterior rays, 

 in an interradial position (see figs. 26-28, p. 69, and pp. 110-111). 



Interradial radials. In the genus Promachocrinus (which has 10 radials instead of 

 the usual 5), the radials which lie in the primitive radii, as determined by 

 the orientation of the centrodorsal and of the basal rays, in contrast to the 

 radials which lie over the basal rays (see figs. 505, p. 371, and figs. 551a, &, pi. 

 5, and pp. 191-194). 



Interradial ridges. On the centrodorsal; the ridges sometimes developed in the 

 interradial portion of the lateral surface (see figs. 9, p. 65, 191, 192, 194, 196, 

 p. 237, 203, 204, p. 239, 215, 216, p. 241, 227, p. 245, and 558, pi. 5, and pp. 

 230-232). 



Interradial spoutlike processes. The interradial processes of the rosette (see figs. 

 577, 578, pi. 10, and 589, 590, pi. 14, and pp. 320-322). 



Interradial structures. Structures developed in the interradial portions of the 

 ventral surface or sides of the disk or between the radials. 



Interradials. (1) Plates developed between the radials, and therefore lying in the 

 radial circlet; among the comatulids they are found well developed only in the 

 young of the species of Thaumatocrinus and of Promachocrinus; in the young 

 of species belonging to other genera interradials, when present at all, are 

 resorbed soon after formation (see figs. 115-118, p. 183, and 122, p. 191). 



(2) Dermal plates developed in the interradial perisome, but entirely with- 

 out the basal circlet; such plates are common in the species of the family 

 Comasteridae, and are often found in species belonging to other families, as for 

 instance in Antedon blfida, A. dubenii and A. moroccana; these are more prop- 

 erly known as interprimibrachial plates (sec figs. 104, p. 167, and 412, p. 317, 

 and pp. 335-339). 



Interradius. An interambulacral area. 



Intersegmental pores. Pores leading inward between the ossicles of the division 

 series and the arm bases, by which the disk is furnished with a supply of fresh 

 water when the division series and arm bases are in close lateral apposition 

 (see figs. 14, p. 65, 95, p. 157, 112, p. 179, and 123, p. 192). 



Intersyzygial interval. The interval between successive syzygies expressed in terms 

 of oblique muscular articulations; the number expressing the intersyzygial 

 interval is the number of oblique muscular articulations occurring between two 

 successive syzygies (see figs. 30, p. 71, and 35, p. 73), 



Intertentacular area. An Interambulacral area. 



Intrapalmar. See Interambulacral. 



Intraradial commissure. See Commissure. 



