72 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



c 2 . First 2 ossicles following the radials united by synarthry; lowest pinnule on the second or 

 fourth ossicle following the radials, and always a pinnule on the following ossicle; arms 

 very long and slowly tapering; centrodorsal flattened hemispherical or very low conical 

 (vol. 1, pt. 2, fig. 1016, pi. 6; fig. 1158, pi. 25) (of general occurrence, but absent from 

 the Arctic and north and east Pacific; sublittoral to abyssal, but chiefly in deep water) 



Pentametrocrinidae (pt. 5). 



6 2 . Centrodorsal long conical, about as high as broad at the base, with the cirrus sockets arranged 

 in definite columns; first syzygial pair very obliquely wedge-shaped, and the immediately 



succeeding brachials triangular (East Indies; deep water) Atelecrinidae (pt. 5). 



a 2 . Ten or more arms. 



&'. No axillaries, each of the 10 radials bearing an undivided arm (of general occurrence, but 



absent from the Arctic, north and east Pacific, and west Atlantic; deep water) 



Pentametrocrinidae (pt. 5). 

 ft 2 . The second ossicle following each radial is an axillary. 



c 1 . The lowest pinnules bear a comblike structure at the distal end (vol. 1, pt. 2, pp. 311, 319; 

 pi. 17) ; mouth usually more or less near the margin of the disk, and anal tube usually 

 more or less central (vol. 1, pt. 2, pi. 24) (Japan and Polynesia to New Zealand and 

 Tasmania, westward to the whole east coast of Africa; northwestern Africa and south- 

 western Europe; North Carolina to Brazil; chiefly littoral and sublittoral, but a few species 



are found in fairly deep water) Comasteridae, p. 76. 



c 2 . No comblike structure on the lowest pinnules; mouth approximately central and anal tube 



more or less marginal (vol. 1, pt. 2, pp. 346, 349). 

 d 1 . Ventral surface of the outer pinnules (as seen with a hand lens) without conspicuous 



plates; middle and outer pinnules not stiffened and sharply carinate. 

 e 1 . Fourth and following brachials always bearing pinnules; first syzygial pair, composed 

 of brachials 3 + 4, oblong, squarish, or slightly wedge-shaped; immediately following 

 brachials more or less oblong; cirrus sockets never bordered ventrally by a horse- 

 shoe-shaped ridge, or flanked with high angular elevations. 

 P. Elements of the IBr series united by syzygy; usually more than 10 arms (Ceylon to 



north Australia and Japan; littoral and sublittoral) Zygometridae (pt. 4). 



/ 2 . Elements of the IBr series not united by syzygy. 

 g l . Ten arms. 



h l . Brachials beyond the fourth exceedingly short, several times as broad as long, 



with almost or quite parallel ends. 



i l . None of the earlier pinnules enlarged; proximal and genital pinnules similar 

 and subequal, and longer than the distal (vol. 1, pt. 2, fig. 279, p. 213). 

 rather stout, and more or less carinate; cirri short, stout, strongly curved, 

 and wholly without dorsal processes; brachials usually, but not always, 

 with middorsal carinate processes (Japan and Polynesia to tropical Aus- 

 tralia, and westward to east and south Africa; St. Helena; Caribbean Sea 

 to Brazil; chiefly littoral, but in the Caribbean Sea occurring in rather 



deep water) Tropiometridae (pt. 4). 



t 2 . P 3 or P 2 or both stouter and longer than the following pinnules; distal pin- 

 nules longer than the genital pinnules; genital pinnules never carinate in the 

 outer portion; cirri slender or stout, often strongly curved, always with 

 dorsal spines or tubercles on the distal segments; brachials never with mid- 

 dorsal carinate processes (vol. 1, pt. 2, pp. 115, 117) (Japan and Polynesia 

 to tropical Australia and the Bay of Bengal; littoral and sublitoral). 



Himerometridae (pt. 4). 

 h*. Brachials beyond the fourth wedge-shaped or triangular, commonly as long as 



broad, and never more than twice as broad as long. 



t 1 . Middle, and almost invariably also the outer, cirrus segments each with a 

 pair of dorsal spines or tubercles, one on either side of the median line 

 (Japan and Polynesia to Australia, westward to east and south Africa; 

 Caribbean Sea; littoral and sublittoral) Colobometridae 'pt. 4\ 



