86 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



First inner pinnule (P ) . The first pinnule developed on the inner side of the free 

 undivided arm; it is usually borne by the fourth brachial (Br 4 ), which is the 

 epizygal of the first syzygial parr (Br 3+4 ) ; in several genera this pinnule is nor- 

 mally absent; it is always one of the last to be developed. 



First pinnule (PJ. The first outer pinnule of the arm, borne by the second brachial 

 (Br,) ; in certain genera this pinnule is normally absent (see fig. 6, p. 63, and 

 pp. 107, 108). 



Food grooves. See Ambulacra. 



Fossse. The depressions lodging the muscles and ligaments in the articular faces of 

 muscular articulations. 



Free Irachials (Br). The ossicles of the undivided arms, as contrasted with the 

 ossicles of the division series. 



Free undivided arms. The arms beyond the outermost axillary. 



Fulcral ridge. On the Transverse Ridge, the narrow vitreous ridge upon which the 

 actual contact takes place at the muscular articulations. 



G. 



Genital pinnules. The pinnules bearing the gonads; the middle pinnules; these 

 follow the oral pinnules, and precede the distal pinnules (see figs. 1, p. 60, 

 6, 8, p. 63, and pp. 112-113). 



Grooveless arms. Arms in which ambulacral grooves are wanting; these are found 

 in certain of the Comasteridse; the left posterior ray is the one most commonly 

 found bearing grooveless arms; often the right posterior is also similarly modi- 

 fied, and the condition may extend to the posterior half of the lateral rays. In 

 species with very many arms all of those borne by the left posterior ray may 

 be grooveless, and there may also be several grooveless arms among those on 

 all the other rays. The anterior ray as a whole is never grooveless, though in 

 species with very numerous arms some of those on the anterior ray may be 

 grooveless; in such instances there are always fewer grooveless arms on the 

 anterior than on any of the other rays (see fig. 45&, p. 79, and pp. 110-111). 



Groove trunks. The ambulacra upon the disk before division (see figs. 15-19, p. 67, 

 and 22-24, p. 69). 



(1) Primary groove trunks are the five ambulacral grooves which arise 

 from the mouth ring; after these divide they resolve themselves into ten 

 secondary groove trunks' (see figs. 15-19, p. 67, and 22-24, p. 69). 



(2) Secondary groove trunks. The groove trunks between the first and 

 second divisions (see figs. 17, p. 67, and 24, p. 69). 



This term is sometimes used for 'all the groove trunks beyond the first 

 division collectively. 



H. 



Habitus. The general appearance. 

 Hard parts. A comprehensive term used to include all the skeletal elements visible 



externally. 

 Heterotypic arm division. Arm division in which the IBr series is interpolated but 



the following extraneous, as in Isocrinus or Pentacrinites. 

 Hypozygal. The proximal ossicle of a syzygial pair. 



