86 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



First inner pinnule (?„). — The first piiimile developed on the inner side of the free 



undivi<lcd arm; it is usually borne by the fourth brachial (Br J, which is the 



opizyi:iil of tlio first syzygial pair (Br3+<); in several genera this pmnulo is nor- 



midly 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. 

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



muscular articulations. 

 Free hracJdals (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 pumulos; these 

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

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



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

 in ccrtam of the Comasteridae; 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 

 aU 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 arc 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. 

 Hahitus. — The general appearance. 

 Hard parts. — A comprehensive term used to include all the skeletal elements ^-isible 



externally. 

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



the following extraneous, as m Isocrinus or Pentacrinites. 

 Hypozygal. — The jjroximnl ossicle of a syzygial jjair. 



