190 



ME. W. PEECT SLADEN ON THE 



Fain. PTERASTERIDiE. 



Synopsis of Genera included therein. 



^Supraclorsal membrane with 

 ! muscular fibrous bands. 

 Actino-lateral spines form--{ 

 ing a free independent late- 

 ral fringe ; not merged in 

 the actinal floor. 



/'Muscular bands not reticu- 



I lated. 



I Membrane usually contain- 



y PtE RASTER. 



Ambulacral spines 

 forming trans- 

 verse combs. 



Spines united by 

 web. 



ing spicules. 



No muscular fibrous bands 

 in the supradorsal mem- 

 brane. 



Actino-lateral spines merged 

 in the actinal floor. 

 ^ No lateral fringe. 



Muscular bands regularly ] 



reticulated. I Ret aster. 



\JSo spicules in membrane. J 



/'Paxillae-spinelets (15-30), "j 

 long and. hair-like, protru- 

 ding freely through the 

 membrane. | 



Ambulacral spines part hori- ^Marsipaster. 

 zontal. 



1 pair of secondary mouth- 

 spines ; united by web to 

 mouth-spine series. ^ 



6)^ 

 11- 



Paxillfe-spinelets (5 

 short, robust, not protrii 

 ding. 



Ambulacral spines perpendi- 

 cular. 



3 pairs of secondary mouth- 

 spines, free and indepen- 

 dent. 



^Oai-ypt raster. 



Ambulacral spines 

 not forming trans- 

 Terse combs. J 



Spines indepen- ' 

 dent, and not 

 united by web. 



( Nidamental cavity spacious. Supradorsal membrane well- \ 

 developed. Muscular fibres present. Spiracula present. I -rr 



I Spinelets of paxilloj short, not protruding through, but [ -n-YMENASTER. 

 supporting, the membrane. J 



Nidamental cavity aborted. Supradorsal membrane rudi-~| 



mentary. No muscular fibres. No spiracula. Spinelets -r, 



-- ■ - - '■ . r. , . '^ Benthasteb. 



No muscular fibres, 

 of paxillie fascicular, protruding a great portion of their 

 i^ length naked through the membrane, 



1 



Hitherto this family has been represented by a very limited 

 number of forms, only nine species being on record. Eight of 

 these belonged to the genera Pteraster and Betaster ; and the ninth 

 was the type and solitary representative of Hymenaster, a genus 

 established by Sir "Wyville Thomson for a remarkable Asterid dis- 

 covered during the cruise of H.M.S. ' Porcupine.' 



Thirty-four species of Pterasteridse have been obtained by 

 the ' Challenger,' only two of which were previously known. 

 Of the thirty-two new species, three belong to Fteraster, four to 

 Metaster, and the remarkable number of twenty to Hymenaster, a 

 genus which is now found to possess a world-wide distribution in 

 deep waters. The remaining five species are representatives of 



