494 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



largcnient of ihe dorsal sides of the segments, sometimes resulting in a keel as in 

 Sarametra triserialis, rarely in a high crest as in Adelometra or in distinct dorsal spines 

 as in Eumorphometra jraseri. Corresponduigly, the opposing spine is usually fairly 

 well developed. However, in a few cases, as in some species of Psathyrometra and 

 Caryometra, the cirri taper to a point, the outer segments remaining very elongated and 

 without distal enlargements or even an opposing spine. Leptometra phalanginm ap- 

 proaches this extreme form, with no opposing spine but the terminal segment still 

 claw-like and slightly curved. In L. celtica the distal segments are relatively shorter 

 with a small development of dorsal processes. 



The proximal pinnules are usually slender and delicate with more or less elongated 

 segments after the basal two or three (rarely up to five). The only exception to this 

 is Cyclometra, in which the pinnules have more numerous and shorter segments, up to 

 45 with a length of 19 mm. in Pi of C. flavescens, where the same pinnule of the other 

 species averages just under 20 segments and about 9 mm. length. However, Poliometra 

 prolixa also has Pi with up to 45 segments, but whereas in Cyclometra most of the seg- 

 ments are barely longer than wide, in Poliometra, after the first five to seven, the seg- 

 ments "rapidly become elongated and excessively long and slender distally." Lepto- 

 metra phalangium has up to 35 segments in Pi but few of the other species have over 25. 



Pi is completely absent in Balanometra and Kempometra. 



P2 is shorter than Pi in Psathyrometra, Eumorphometra and Poliometra, similar in 

 Anisometra and Leptometra and longer in Zenometra, Sarametra, and Eometra. Of the 

 two species of Cyclometra, flavescens has P2 shorter and multicirra longer, while in 

 Caryometra it is usually shorter but may be similar or longer. 



KEY TO THE GENERA OF ZENOMETRINAE 



[modified by A.M.C.] 



(Three genera have had to be included twice in this key, Poliomelra because of the discovery of an 

 aberrant specimen with bare interradial spaces on the centrodorsal, Psathyrometra because of the 

 considerable range its species show in the positioning of the cirrus sockets, and Hybometra because of 

 our ignorance of its cirri. — A.M.C.) 



a'. Centrodorsal with the radial areas delimited by distinct ridges, grooves or flat spaces which 

 separate the proximal parts at least of the lateral columns in adjacent radial areas. 

 6'. Cirrus sockets in two parallel and usually contiguous columns in each radial area, 

 c'. Division series and proximal brachials with conspicuous spinous borders. 



(P. The paired columns of cirrus sockets separated by broad high ridges; adjacent division 

 series and lower brachials in close lateral contact (from St. Lucia to the Gulf of Mexico 



and the coast of Georgia; 308-804 meters) Zenometra (p. 495) 



(P. The paired columns of cirrus sockets separated by narrow interradial spaces which are 

 plane; division series not in lateral contact (Antarctica; 219 meters). 



Anisometra (p. 499) 

 c'. Division series and proximal brachials smooth. 



d". Centrodorsal long conical, its height much greater than its basal diameter; Pi absent 



(Phihppine Islands; 142-150 meters) Balanometra (p. 500) 



(P. Centrodorsal conical but not higher than wide; Pi present. 

 «'. More than 10 arms; distal cirrus segments shorter than broad, with prominent dorsal 



keels (Kei Islands; 256 meters). Adelometra (p. 503) 



e^. 10 arms; distal cirrus segments very long and quite without dorsal processes (Indian 

 Ocean to the East Indies, Sea of Japan, Alaska, west central America, the Galapagos 

 and Hawaiian Islands; 366-2903 meters) Psathyrometra (p. 510) 



