56 ECHIN0DERM8 OF THE BRITISH ISLES 



Marginal plates not tumid ; side of arm very higli. Dorsal side 

 of arm, between marginals, not very narrow ... 7 

 7. Adambiilacrals strongly projecting into the ambulaoral furrow; 

 median fin-row spine prolonged 



3. Bathybiafiter Danielssen and Koren 

 Adaml)ulacrals less strongly projecting into the ambulacral 

 furrow ; median furrow spine not prolonged 



2. Psilaster S laden 



Fig. 31. — Pedicellariw from oral interradial area of Dytaster rigidus. 



x8. 



1. Astropecten Linck. 



Disk fairly large ; arms low, broad, of medium length. Upper 

 marginal plates with fine grains and, sometimes, with one or more 

 larger, erect, conical spines ; lower marginal jDlates with flat 

 spines, which form a distinct fringe all round the edge of disk 

 and arms. Oral interradial areas ver\^ small, with only 1-3 

 series of interradial plates which do not continue beyond the 

 basal part of the arms, thus the adambulacral and lower marginal 

 plates join each other in almost the whole length of the arm. 

 Madreporite naked. No pedicellarise. 



A great number of species, especially from troj^ical seas, 

 belong to this genus. In British seas only two species have been 

 found. Four more species occur in the Mediterranean, two 

 of which, viz. A. aranciacus (Linn.) (Syn. A. aurantiacus 

 Tiedemann ^) and A. bisinnosus Otto, also have been found in 

 the Atlantic, the former at the Canaries, the latter at the Azores. 

 A. aranciacus has also been recorded (by Perrier) from the Bay 

 of Biscay, but the identification has been found to be incorrect. 

 (This is certainly also the case with a record of Astroj^ecten 



^ The Asterias aurantiaca (Linn.), recorded from the Clyde sea area 

 (Chumley), is certainly not the Astropecten aranciacus ; one may perhaj^s 

 suggest it to bo Stichastrella rosea. 



