70 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



e 1 . 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 2 . 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. 



fr 2 . 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 1 . 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 l . Cirrus segments either without dorsal processes, or the distal each with a median cari- 



nation or carinate spine. 

 e 1 . Arms 5 in number, no axillaries being present (Japan to the Moluccas and the Lesser 



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



e 2 . Arms 10 or more, the second postradial ossicle being always axillary. 

 f 1 . Elements of the IBr series united by syzygy (Japan to tropical Australia and west- 

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



T 2 . Elements of the IBr series not united by syzygy, but by synarthry. 



g l . 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 2 . 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 2 . 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 2 . All of the pinnules prismatic with a sharp, or sharply rounded, dorsal keel (Japan, Aleutian, 

 Hawaiian, and Galapagos 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). 



d l . 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 2 . Ventral surface of Ihe pinnules protected by conspicuous side and covering plates easily 



visible with a hand lens. 



e 1 . Pj very delicate, flexible and weak, with the first 2 segments enormously enlarged and 

 the remainder very small and about as long as broad; P 2 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 2 . PI not delicate nor weak, its first 2 segments not noticeably enlarged; P 2 like P 3 or, 

 more 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 usually more than 25 segments, of which the distal arc 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). 



