PART 5 A MONOGRAPH OF THE EXISTING CRIXOIDS 511 



lower brachials are high and narrowly rounded dorsally, not in hitoral contact; their 

 borders are smooth; all the pinnules are present. 



Type species. — Antedon fragilis A. H. Clark, 1907. 



Geographical range. — From Zanzibar to the East Indies, thence northward to 

 Japan and the Aleutian Islands, eastward to the Gulf of Alaska and southward to the 

 coast of Central America and the Galapagos Islands and from the Hawaiian Islands. 



Bathy metrical range. — From 366 to 2903 meters. 



Thermal range.— Prom 0.39° to 13.3° C. 



Remarks [bj' A.M.C.]. — The tj^^e species, rsathyrometrafragilis, has flat bare areas 

 on the centrodorsal interradially between the columns of ciiTUs sockets. Most of the 

 other species in the genus are similar in this respect but Mr. Clark has also included 

 P. congesia (which I have not seen), which has the cirrus sockets crowded all over the 

 centrodorsal and not forming radial gi-oups. In two species — mira and graciUima — ^the 

 interradial areas may be grooved, at least in larger specimens. Following examination 

 of some specimens of mira, minima, graciUima and anomala I have made some alterations 

 to the key to try to make allowance for differences of size. With so few specimens 

 known of the three last-named species the extent of then- variation cannot be 

 appreciated. 



KEY TO THE SPECIES OF PSATHYROMETRA 



[modified by A.M.C.] 



a'. Centrodorsal higher than broad, often markedly so (Monterey Bay, California, to Alaska, thence 

 westward to the western Aleutian Islands and southward to southern Japan; 439-2903 meters). 



fragilis (p. 512) 

 6'. Centrodorsal with four columns of cirrus sockets in each radial area (from northern Japan 



northward and eastward to southeastern Alaska; 439-974 meters) forma fragilis 



6^. Centrodorsal with three columns of cirrus sockets in each radial area (geographical range of the 



species, but in deep water; 1210-2903 meters) forma borealia 



a*. Centrodorsal not higher than broad. 



6'. Centrodorsal with four columns of cirrus sockets in each radial area. 



c'. Centrodorsal with the radial areas separated by narrow interradial lines; cirrus sockets not in 

 contact with each other (Galapagos Islands and the western coast of Central America; 



704-1014 meters) bigradata (p. 515) 



c'. Centrodorsal with no indication of division into radial areas, and all the cirrus sockets closely 



crowded (Hawaiian Islands; 965 meters) congesta (p. 517) 



t^. Centrodorsal with not more than three columns of cirrus sockets in each radial area, 

 c'. Centrodorsal a broadly truncated cone with three complete and equal very closely placed 

 columns of 4 or 5 (usually 4) cirrus sockets in each radial area, the radial areas being 

 separated by interradial flat spaces; size usually large, the arms up to 150 mm. in length; 

 cirri with 35-40 segments (north-eastern part of the Sea of Japan; 713-742 meters). 



erythrizon (p. 518) 



c'. Centrodorsal conical, sometimes slightly rounded off at the tip, with 2, or 2 lateral and a 



partial median, columns of cirrus sockets in each radial area, the radial areas being separated 



by interradial spaces which may be slightly convex, flat or grooved; arms not known to 



exceed 100 mm. in length; cirri probably with not more than 30 segments. 



d}. Interradial bare areas of the centrodorsal narrow, hardly, if at all, wider than the individual 



peripheral sockets. 



e'. Interradial areas often grooved; centrodorsal fairly high conical, the ratio of basal diameter 



to vertical height rarely more than 1.5:1; cirrus sockets fairly close together in each 



radial area (from off Zanzibar to the East Indies and southern Japan; 366-924 meters). 



mira (p. 519) 



e". Interradial areas plane or slightly raised; cirrus sockets spaced radially, or if close together 



then the centrodorsal is low with the ratio of diameter to vertical height about 1.7:1. 



