52 ECHINODERMS OF THE BRITISH ISLES 



3. Oral interradial areas covered with spiniform granules. Adambu- 



laeral ])lates with papilliform spinelets on the outer part ; 

 terminal plate very small and inconspicuous, unarmed ; fourteen 

 cribriform organs ..... Thoracaster Sladen 

 Oral interradial plates usually naked ; adambulacral plates with 

 a single series of spines on furrow margin only. Terminal 

 plate large, with conspicuous spines ; 1-11 cribriform organs 4 



4. Dorsal side only with simple spines ; a conical elongation in the 



middle. Oral interradial plates not imbricated ; ambulacral 

 furrow wide ; 1 cribriform organ Porcellanaster Wy v. Thomson 

 Dorsal side with paxillae, at most with a slight peak in the middle. 

 Oral interradial plates imbricated and arranged in columns ; 

 ambulacral furrow narrow ; 3 or more cribriform organs . 5 



5. A series of robust spines along the median line of rays 



Styracaster Sladen 

 No spines on middle line of rays . . Hyphalaster Sladen 



Of the genus Porcellanaster Wyv. Thomson (Syn. Caulaster 

 Perrier) four species have been found in the said area, viz. 

 P. {Caulaster) Sladeni Perrier (32° 38' N. ; 12° 9' W., 1435 m.) ; 

 P. (Caulaster) pedunculatiis Perrier (42° 50' N. ; 2° 57' W., 

 2020 m.) ; P. inermis Perrier (38° N. 27° W. ; 16° N. 20° W., 

 2995-3200 m.), and P. granulosus Perrier (19°-16° N. ; 20° W., 

 2320-3200 m.). Of the genus Styracaster Sladen four species, viz. 

 St. spinosus Perrier (40° N. 18° W. ; 38° N. 27° W., 2995-4360 m.) ; 

 St. Edwardsi Perrier (15° 48' N. ; 22° 43' W., 3655 m.) ; St. 

 horridus Sladen (44° N. 10° W. ; 31° N. 24° W. ; 2° S. 14° W., 

 4300-5400 m.), and St. elongatus Koehler (40° N. 18° W. ; 38° N. 

 23° W. ; 37° N. 20° W., 4020-5360 m.). Of the genus Hyphalaster 

 Sladen three species, viz. H. Parfaiti Perrier (Syn. H. Antonii 

 Perrier) 46° N. 9° W. ; 38° N. 27° W. ; 16° N. 24° W., 2995-5430 m.) ; 

 H.fortis Koehler (40° N. 18° W. ; 16° N. 24° W., 3890-4360 m.), 

 and H. gracilis Koehler (31° N. 24° W., 5413 m.). Of the genus 

 Thoracaster Sladen one species, Th. cylindratus Sladen (Syn. 

 Pseudaster cordifer Perrier) (off Portugal, Josephine Bank, 

 Canaries, 4275-4392 m.), and of the genus Alhatrossaster Ludwig 

 one species, A. Ricliardi Koehler (12° N. 33° W., 6035 m.). 



For descriptions of all these species reference must be made 

 to the works of Sladen (" Challenger "), Perrier ('"Talisman"), 

 and Koehler (Monaco, Fasc. xxxiv.). 



The genus Ctenodiscus has recently been maintained rather 

 to belong to the family Goniopectinidce, which is distinguished 

 from the true Porcellanasterids mainly by having cribriform 

 organs between all the marginal plates and by having 

 fimbriated or fasciolar channels between the oral interradial 



