88 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Interamhulacral areas (also called Interpalmar areas) .—l:\ie subtriangular areas on 

 the disk between the ambulacral furrows (see figs. 1, p. 60, 2, p. 61, and 15-18, 

 p. 67, and pp. 110-111). 

 InterarticuUir ligament fossx. — The usually more or less triangular fossae seen on the 

 articular face of an ossicle joined to another ossicle by a muscular articulation 

 wliich lie just distal (ventral) to the transverse ridge, one on either side of the 

 central canal (see figs. 9, 10, p. 65, 31, 32, p. 71, and 431, 432, p. 349, and 

 p. 114.) 

 Interarticular pores. — In the pentacrinit(>s, the pores between the columnals in the 

 upper (proximal) part of the column; these are mterradial (mtcrangular) in 

 position; they do not communicate with the central cavity of the column but 

 end blindly, usually at some distance from it, just as do the homologous sub- 

 radial clefts seen in certain comatulids (see fig. 127, p. 197, and p. 232). 

 Interhrachial. — Occurring on the perisome between the brachials; that is, between 



the ossicles of the undivided arm. 

 Interhrachials (iBr). — Dermal plates occurring in the perisome between the brachials 



(see figs. 104, p. 167, 115, 118, p. 183, and 122, p. 191, and pp. 339). 

 Iniercostals. — Small dermal i)lates occurring in the perisome between the IBr series; 

 these are, among the comatulids, commonly, but incorrectly, referred to as 

 interradials (see fig. 104, p. 167). 

 Interdistichals. — Small dermal plates occurring in the perisome between the IIBr 



series. 

 Intermuscular furrow. — On the articular faces of two ossicles joined by a muscular 

 articulation, the furrow separating the muscular fosste; it lies along the dorso- 

 ventral axis (see figs. 10, p. 65, and 431, p. 349). 

 Intermuscular groove. — See Intermuscular furrow. 

 Intermuscular midradial furrow. — See Intermuscular furrou\ 



Intermuscular notch. — On the articular faces of two ossicles joined by a muscular 

 articulation, a notch separating the distal portions of the muscular fossae (see 

 figs. 31, 32, p. 71, and 431, p. 349). 

 Intermuscular ridge or septum. — On the articular faces of two ossicles joined by 

 a muscular articulation, a narrow ridge separating the muscular fossae in the line 

 of the dorsoventral axis; in many forms this is replaced by an intermuscular 

 furrow, or there may be a ridge dorsally which transforms into a furrow vcntrally 

 (distally) (see figs. 9, p. 65, 31, 32, p.'71, and 432, p. 349). ' 

 Internal arm. — Any arm arising from the IIBr (or subsequent) division series, except 

 the two outermost in reference to the IBr series, more rarely in reference to the 

 IIBr scries (see figs. 616, p. 87, and 78, p. 131). 

 Internal face of the radial. — (1) The entire surface of the radial within the distal 

 edge of the muscular fossaa of the articular faces. 



(2) The innermost portion of the preceding, which lies in a plane parallel 

 with the dorsoventral axis of the animal (see figs. 437, 438, 446, p. 351, 549&, 

 551a, 554, pi. 5, and COO, pi. 177). 

 Intemodal. — In the pentacrinites, a columnal which does not bear < irri (sec fig. 127, 

 p. 197.) 



