ASTEROIDEA 95 



always provided with a sucking disk. The number of the rays 

 five or many. 



Six families belonging to this order are represented in 

 British seas, and probably two more, viz. the Chcetasteridce 

 and MyxasteridcB, will be found to occur there also. Of the 

 former, one species, Chcetaster longipes (Retzius), has been 

 found in the Bay of Bisca}^ (130 m.) (elsewhere found in the 

 Mediterranean, along the Moroccan coast, and at the Azores, 

 ca. 30-1140 m.);i of the latter, one species, Myxaster Perrieri 

 Koehler, has been found in the Bay of Biscay, 1300 m. ; another, 

 Myxaster sol Perrier, between the Canaries and the Cape Verde 

 Islands, 1400-1550 m. (the two species are easily distinguished 

 by the number of arms, M. Perrieri having 6, M. sol 9-10 arms). 

 These two famihes are therefore included in the key, but not 

 otherwise treated here. 



Key to the families of Spinulosa known from or likely to be 

 represented in the British seas. 



1. Body more or less flattened, with a distinct edge forming a sharp 



limit between dorsal and oral side ..... 2 

 No distinct edge, no sharp limit between dorsal and oral side 4 



2. A finlike membrane along the edge of the body ; paxillse of the 



dorsal side covered by a membrane which lies like a roof 

 over the whole dorsal side . . III. Fam. Pterasteridce 



The edge of the body formed by the more or less distinct marginal 

 plates, not by a finlike membrane. No membrane forming a 

 roof over the dorsal side ...... 3 



3. Marginal plates rather indistinct. Dorsal side covered with 



scalelike, imbricating plates carrying small spines placed in 

 irregular groups or forming very low paxillae 



II. Fam. Asterinidoe 

 Marginal plates distinct, paxillae-like, in a double series. Dorsal 

 side with small, independent plates carrying slender paxillse 



I. Fam. Radiasteridce 



4. Disk very small ; arms 5, long, slender, cylindrical ; spines 



small, singly or in very low, paxillse -like groups . . 5 



Disk fairly large ; arms 5 or more ; spines rather long, forming 



very distinct, conspicuous paxillse ..... 6 



5. Spines single or in small groups which do not show a regular 



serial arrangement. Spines not glassy 



VI. Fam. Echinasteridce 

 Spines in very dense groups, forming low paxillse which are 

 arranged in very regular longitudinal series. Spines glassy 



Fam. Chcetasteridce 



^ The statement of its occurrence at the Bermuda Islands rests on a 

 misidentification ; the Bermuda form is Chcetaster nodosus Perrier, not 

 Ch. longipes. 



