252 ECHINODERMS OF THE BRITISH ISLES 



the next only about half that length, and the lowermost one 

 quite small, hardly to be distinguished from a tentacle scale. 

 Mouth shields about as broad as long, with a small side lobe and 

 a straight outer edge. Mouth papillae very small, close set. 

 Genital slits reaching to edge of disk, papillate only along their 

 outer interradial edge. Colour in life bright orange. Most 

 specimens known are of a small size, up to 18 mm. diameter of 

 disk, but a specimen taken in the Bay of Biscay (" Princesse 

 Alice ") is recorded measuring 40 mm. diameter of disk. Arms 

 ca. three to four times as long as diameter of disk. 



Development and biology unknown. 



In British seas this species has been found off S.W. Ireland, 

 50° 34' N., 11° 19' W., ca. 1200 m. (" Helga "), and in the Faroe 

 Channel, warm area ("Knight Errant", "Triton", "Michael 

 Sars "), ca. 800-1300 m. Also found in the Bay of Biscay and 

 at the Azores, 1490-1740 m. (" Princesse Alice "). Further 

 known from the east coast of N. America, ca. 280-1725 m. 



4. Ophiomusium Lyman. 



Disk mostly covered with larger, thick, often granulated 

 plates, not with imbricating scales. No arm combs. Arms rigid. 

 Dorsal and ventral plates of arms rudimentary, arm spines very 

 small, rudimentary. Tentacle pores confined to the proximal 

 arm joints. Second tentacle pore within the mouth slit, not at 

 all visible from the outside. 



Only one species know^n from the British seas, but four others 

 are more or less likely to occur there also, namely : Ophiomusium 

 africanum Koehler, found S.W. of the Cape Verdes, 219 m. 

 (only one specimen known, " Princesse Alice ") ; 0. armigerum 

 Lyman, off Madeira, 2970 m. (" Challenger "), also known from 

 the Southern Atlantic and the West Indies, ca. 1580-3960 m. ; 



0. planum Lyman, from the Bay of Biscay and the Azores down 

 to the Cape Verdes, ca. 260-4060 m., also know^n from the West 

 Indies and the Bay of Bengal, ca. 2325-5000 m. ; 0. scalare 

 Lyman, Cape Verde Island, 225 m. (a young specimen only, 

 "Talisman"), elsewhere only known from the Indo- Pacific, 

 where it is widely distributed, ca. 200-1100 m. These species 

 are thus distinguished : 



Key to the species of Ophiomusium known from or likely 

 to occur in the British seas. 



1. Only 2 pore pairs ; no papillae along genital slits. . . 2 

 3-4 pore pairs ; papillae along genital slits ; a rudimentary arm 



comb may be present ....... 4 



