70 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



e'. Arms 10 or more; all the division series 2 (1 + 2); genital pinnules composed of short 

 and very broad segments (Burma and the Andaman Islands to tropical Australia; 



littoral) Comactiniinae, p. 293. 



e'. Always more than 10 arms; at least some, and occasionally all, of the division series 

 of 4 elements; genital pinnules unmodified (Polynesia and the Philippines to tropical 



Australia, and westward to the Maldives; littoral) Comasterinae, p. 404. 



fc2. No comblike structure on the lowest pinnules; mouth always central or subcentral, and anal 

 tube more or less marginal; sacculi always present, though sometimes in small numbers. 

 c'. Only the oral pinnules prismatic, and these often keeled only at the base (Japan and 

 Polynesia to Tasmania and westward to east and south Africa; Caribbean Sea; littoral 



and sublittoral) Mariametrida (pt. 4). 



d'. Cirrus segments either without dorsal processes, or the distal each with a median cari- 

 nation or carinate spine, 

 e'. Arms 5 in number, no axiUaries being present (Japan to the Moluccas and the Lesser 



Sunda and Andaman Islands; sublittoral) Eudiocrinidae (pt. 4). 



e'. Arms 10 or more, the second postradial ossicle being always axillary. 

 p. Elements of the IBr series united by syzygy (Japan to tropical Australia and west- 

 ward to Ceylon; littoral and sublittoral) Zygometridae (pt. 4). 



p. Elements of the IBr series not united by .syzygy, but by synarthry. 



g'. Arms 10 or more; if there are more than 10 arms the IIBr series are 4 (3 + 4) 

 (Japan and Polynesia to tropical Australia, and westward to east Africa; littoral 



and sublittoral) Himerometridae (pt. 4) . 



g^. Always more than 10 arms; all the division series 2 (Japan and Polynesia to 

 tropical Australia, westward to east Africa; littoral and sublittoral). 



Mariametridae (pt. 4). 

 d^. 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 Aus- 

 tralia, westward to east Africa; Caribbean Sea; littoral and sublittoral). 



Colobometridae (pt. 4). 



c'. All of the pinnules prismatic with a sharp, or sharply rounded, dorsal keel (Japan, Aleutian, 



Hawaiian, and Gahipagos Islands to Tasmania and westward to east and south Africa; 



in the Atlantic north to the Bay of Biscay and the Caribbean Sea; chiefly in deep water 



and sublittoral, but a few species are littoral) Tropiometrida (pt. 4) . 



rf'. Ventral perisome of the pinnules not protected by conspicuous side and covering plates; 

 cirri stout, without dorsal processes; 10 arms (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). 

 d'. Ventral surface of the pinnules protected by conspicuous side and covering plates easily 

 visible with a hand lens. 

 e'. P, very delicate, flexible and weak, with the first 2 segments enormously enlarged and 

 the remainder very small and about as long as broad; Pj and usually also some of 

 the following pinnules much elongated, enlarged and stiffened, composed of much 

 elongated segments; disk globose, compact, entirely inclosed by a complete pave- 

 ment of plates and readily detached (Japan and Polynesia to tropical Australia and 



the Bay of Bengal; sublittoral) Calometridae (pt. 4). 



e». P, not delicate nor weak, its first 2 segments not noticeably enlarged; Po like Ps or, 

 mure rarely, like Pi, never especially distinguished; disk sunken within the division 

 series, with the ventral surface concave, flat, or slightly convex, and thickly beset 

 with isolated plates. 

 /'. Cirri usually long and slender, rarely of moderate length and rather stout, com- 

 posed of usuaUy more than 25 segments, of which the distal are much shorter than 

 the proximal, broader than long, with conspicuous dorsal spines or carinate processes; 

 surface of the shorter distal segments always light in color and highly polished; a 

 well-marked transition segment usually present Thalassometridae (pt. 4). 



