54 ECHINODERMS OF THE BRITISH ISLES 



furrow wide. Colour of living specimens yellowish. Size up to 

 ea. 5 cm. 11. 



The species appears to reach its full size in the course of three 

 years. Development unknown, but as it has large, yolky eggs 

 it is likely to have direct development, without a pelagic larval 

 stage. It lives on a soft, muddy bottom and fills its stomach 

 with mud, largely, at any rate, by means of the ciliary currents 

 produced by the cribriform organs and the ciliated channels 

 between the oral interradial plates. The fine particles of mud 

 thus brought towards the mouth are imbedded in mucus so as to 

 form strings. 



In British seas this species has been found only in the cold 

 area of the Faroe Channel, 560-1135 m. ("Porcupine"). It is 

 an arctic species, probably circumpolar ; on the Scandinavian 

 coast it is also found at relatively high temperatures, up to 10° C. 

 (not found S. of the Trondhjemsfjord). It occurs at the N. coast 

 of Iceland, at Greenland, and at the East Coast of N. America 

 a little beyond Cape Cod. In the Pacific it extends to Japan 

 and along the W. coast of America down to Chile. The bathy- 

 metrical distribution is ca. 10-1860 m. and probably even more, 

 but it appears to have its main distribution in depths of 

 ca. 50-600 m. 



II. Family Astropectinid^ 



Upper and lower marginal plates well developed, thick, more 

 or less covered with spines or grains. Aboral side covered with 

 paxillse. Oral interradial areas covered with spines. No cribri- 

 form organs, but often with distinct marginal " fascioles ", which 

 are never webbed. Intestine, generally also intestinal caeca 

 present ; anus present or absent. Tube-feet pointed ; ampullae 

 double ; papulae simple. Genital organs mostly confined to base 

 of ray. 



Six genera of this family are represented in the British seas. 

 In addition there is some possibility that tw^o more genera will 

 also be found to occur there, viz. Tethy aster Sladen and Dytaster 

 Sladen (Syn. Crenaster Perrier) ; these two are therefore also 

 included in the key to the genera of Astropectinidae, while not 

 otherwise described here. Of Tethy aster only one species, T. sub- 

 mermi5(Philippi) {Syn. Pluionaster subinermis), occurs in European 

 seas, known from the Bay of Biscay to Morocco and Liberia, and 

 especially from the Mediterranean (60-300 m.). Of Dytaster no 

 less than eight species have been recorded from the North -East 

 Atlantic, viz. Dytaster biserialis Sladen (36° N. 23° W., 3645 m. ; 

 40° N. 18° W., 4360 m.) ; D. parvulus Koehler (37° N. 20° W., 



