MONOGRAPH OF THE EXISTING CKINOIDS. 97 



Perisome. — The noncalcareous integument covering the ventral surface of the 

 animal; in general this term is restrietod so tliat it refers only to the integu- 

 ment covering the ventral and lateral portions of the disk (see figs. 1, p. 60, 

 2, p. 61, 6, p. 63, and 15-18, p. 67). 



Perisomic interradials. — Perisomic plates arismg secondarily between the division 

 scries on the outer (dorsal) surface of the disk (see fig. 104, p. 167, and p. 339). 



Perisomic plates. — More or less irregular plates developed within the cutis (see figs. 

 S, p. 63, 18, 19, p. 67, and 122, p. 191, and p. 195). 



Perisomic sl-eleton. — The dermal skeleton developed in the perisome of the atlult 

 animal. 



Perisomic spicules. — Spicules developed within the cutis. 



Peristome. — The depressed area on the disk immediately surrounding the mouth 

 (see fig. 15, p. 67). 



Perradial. — Same as radial, as contrasted with interradial. 



Phytocrinoid . — See Pentacrinoid. 



Pinnulars. — The segments of the pinnules (see figs. 6-8, p. 63). 



Pinnulation.- — The arrangement of the pinnules (see pp. 112-113). 



Pinnule ambulacra. — The ambulacral grooves on the ventral surface of the pin- 

 nules, in contrast to those on the ventral surface of the arms and of the disk. 



Pinnule socJceis. — The articular facets on the brachials to which the pinnules are 

 articulated; they are in origin degenerate muscular fossae (see fig. 32, p. 71, 

 and p. 273). 



Pinnules. — The slender jointed structures which border the arms (see figs. 1, p. 60, 

 2, p. 61, 3, p. 62, 6, 8, p. 63, and pp. 112-113). 



Plate. — As usually employed this term covers calcareous structures which are much 

 broader than their interior-exterior diameter. 



Plated ambulacra. — Ambulacra which are protected by well-developed side and 

 covering plates (see figs. 7, p. 63, 18, 19, p. 67, and 55, p. 81, and p. 112). 



Plated dislc. — A disk upon which secondary calcareous dermal plates are developed 

 (see figs. 7, p. 63, and 55, p. 81, and pp. 111-112). 



Polar cirri. — See Small mature chri. 



Posterior arm. — See Axis lb and Orientation 3. 



Posterior interradial area. — See Axis and Orientation. 



Posterior radii. — The radii on either side of the anal interambulacral area (see 

 figs. 22-25, p. 69, 117, p. 183, and pp. Ill, 152-161). 



In certain of the Comasteridae the left posterior radius becomes curiously 

 modified, and is then often distinguished simply as the posterior radius, the right 

 posterior radius being considered hi this case as an anterior radius (see figs. 

 27, 28, p. 69, and pp. HI, 152-161). 



Posterior ray. — In the Comasteridae (see Orientation 3). 



Posterior rays. — See Posterior radii. 



Post-palmars. — (I\rBr, Mir, VIBr, etc.)—- Series of two, three, or four ossicles, 

 always ending in an axillary, developed beyond the palmars (IIIBr series). 



When tliis term is used the successive series are designated as first post- 

 pakners (H'Br series), second post-palmars (\rBr series), third post-palmars 

 CV'iBr series), etc. 



