PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 495 



fc 2 . Cirrus sockets in three or more columns, or if in two then the columns are separated and lie at 



the borders of the radial areas converging towards the apex. 



c 1 . Outer cirrus segments broader than long, with dorsal spines; borders of the elements of the 

 IBr series and lower brachials conspicuously spinous (Hawaiian and Nicobar Islands; 



351-643 meters) Sarametra (p. 506) 



c 2 . Outer cirrus segments much longer than broad; edges of the elements of the IBr series and 



lower brachials smooth. 



d 1 . Cirri with up to 40 segments; Pj not much shorter than P! (Indian Ocean to the East Indies, 

 Sea of Japan, Alaska, west central America, the Galapagos and Hawaiian Islands; 



366-2903 meters) Psathyrometra (p. 510) 



<f. Cirri with up to 50 segments; Pi only about a third as long as PI (Arctic; 20-1960 meters). 



Poliometra (p. 572) 

 a 2 . Centrodorsal without interradial ridges, grooves or spaces separating the sockets. 



6'. PI and P a absent; peripheral cirri with not more than 16 segments of which all but the two 

 basal and the penultimate are longer than broad (South Shetland Islands; 830 meters). 



Kempometra (p. 530) 

 6 2 . PI and P a present; peripheral cirri with at least 20 segments. 



c'. Pj and Pj long and slender, flexible distally, with 24-45 segments of which the longest distal 

 are only slightly longer than broad, recalling the oral pinnules of the Heliometrinae (Arabian 



Sea and southwest Africa; 461-2194 meters) Cyclometra (p. 532) 



c 2 . PI and Pi with elongated distal segments. 



d 1 . Longest cirrus segments less than twice as long as wide. 



e 1 . Pi with less than 15 segments; centrodorsal with 15 (rarely 20) cirrus sockets around the 

 periphery; probably all viviparous (Antarctic; 177-490 [?610] meters). 



Eumorphometra (p. 536) 

 e 2 . Pi very attenuate with over 25 segments; centrodorsal with 20 peripheral cirrus sockets 



(arm length about 100 mm.) (off Brazil; 42 meters) Hybometra (p. 550) 



d 2 . Longest cirrus segments over twice as long as wide, often much longer. 

 e 1 . Pi with over 20, usually 25-35, segments. 



/'. Pj tapering abruptly near the base, then very attenuate, all the segments but the first 

 one being longer than broad and the outer ones flared distally (Brazil; 42 meters). 



Hybometra (p. 5.50) 



/ a . Pi not markedly tapering basally, the first 3 to 6 segments not longer than broad, outer 

 segments not markedly flared (north of Scotland to Sierra Leone and the Mediter- 

 ranean; 46-1292 meters) Leptometra (p. 552) 



e 2 . P 2 with up to 17 segments. 

 /'. Peripheral cirri with up to 50 segments; PI with 25-45 segments (Arctic; 20-1960 



meters) Poliometra (p. 572) 



n. Peripheral cirri with up to 35 segments; PI with 10-24 segments. 



0'. PI shorter than Pj, both of them much shorter than P 3 ; cirrus sockets in 10 closely 



crowded columns (Antarctic; 2725-3426 meters) Eometra (p. 592) 



g 1 . P! shorter or longer than Pi but neither shorter than Pa; cirrus sockets in 10 or 15 

 columns (West Indies; 338-777 meters) Caryometra (p. 595) 



Genus ZENOMETRA A. H. Clark 



Antedon (part) P. II. CARPENTER, Bull. Mus. Comp. Zool., vol. 9, No. 4, 1881, p. 152, and following 

 authors. 



Zenometra A. H. CLARK, Smithsonian Misc. Coll., vol. 50, pt. 3, 1907, p. 354 (diagnosis; type species 

 Anledon columnaris P. H. Carpenter, 1881); vol. 52, pt. 2, 1908, p. 233 (undoubtedly occurs in 

 the East Indian region); Bull. Mus. Comp. Zool., vol. 51, No. 8, 1908, p. 247 (same); Proc. U.S. 

 Nat. Mus., vol. 34, 1908, p. 211 (referred to the Antedonidae, restricted), p. 212 (occurs in the 

 West Indies and the Hawaiian Is.), p. 221 (relation to Psathyrometra); Amer. Nat., vol. 42, 

 No. 503, 1908, p. 725 (color); Proc. Biol. Soc. Washington, vol. 21, 1908, p. 136 (referred to the 

 Antedonidae) ; vol. 22, 1909, p. 176 (referred to the Zenometrinae) ; Vid. Medd. Nat. Foren. 

 K0benhavn, 1909, p. 128 (closely related to Leptometra); Proc. U.S. Nat. Mus., vol.40, 1911, 



