OPHIUROIDEA 199 



1. Ophiactis Liitken. 



Disk generally with scattered spines, which do not conceal 

 the rather coarse scales. One to two mouth papillse, not con- 

 tiguous with the generally heart-shaped infradental papilla on 

 apex of jaw. No small plates around the dorsal arm plates. Arm 

 spines rather short, not very coarse, none of them hook-shaped. 

 Genital slits usually well developed. 



The species of this genus are mostly small forms ; several of 

 them propagate by autotomy, and are therefore usually found 

 with one half of the disk and the corresponding arms about to 

 regenerate, and conspicuously smaller than the other half of 

 the disk and its arms. These self- dividing species usually have 

 6 or 7 arms. 



Two species have been found in the British seas, but some 

 more are likely to occur there also, namely : Ophiactis canotia 

 Lyman (off Azores, 1800 m., " Challenger ") ; 0. echinata Koehler 

 (Azores, 800 m., " Hirondelle " ; only one specimen known) ; 

 O. Lymani Ljungman (15° 54' N., 22° 55' W., 91 m. ; elsewhere 

 known from the West Indies) ; 0. profundi Liitken and 

 Mrtsn. (Azores, 650-914 m., " Princesse Alice " ; elsewhere 

 known from the Pacific, ca. 1000-1650 m.) ; 0. nidarosiensis 

 Mrtsn. (hitherto known with certainty only from the Norwegian 

 coasts, ca. 200 m., but very probably the specimen from the Azores 

 recorded as Ophiactis hirta Lym. (" Princesse Alice ", 1095 m.) 

 was really 0. nidarosiensis). Also the Mediterranean species, 



0. virens M. Sars, which occurs likewise at the Azores and down 

 to Cape Verde, may be mentioned, though, as a strictly littoral 

 form, it is not very likely to occur as far north as the British 

 coasts. The main characters of these species are given in the 

 following key. 



Key to the species of Ophiactis known from or likely to 

 occur in the British seas. 



1. Arms 5 . ... . . . . . . .2 



Arms 6-7 ......... 5 



2. One mouth papilla on each side of jaw (Fig. 112) 



1. 0. Balli (Thomps.) 

 Two mouth papillae on each side of jaw .... 3 



3. Dorsal plates of arms triangular, widely separated. {"Monaco ", 



xii. PI. V. 15-16)1 .... O. ec/ima^a Koehler 



Dorsal plates of arms contiguous in proximal part of arms . 4 



1 The single specimen known of O. echinata is a young one, measuring 

 only 2 mm. diameter of disk. It may possibly be only the young of one of 

 the other species loiown from the European seas. 



