196 ECHINODERMS OF THE BRITISH ISLES 



0. Oj^hiacantha hidentata (Retzius). (Fig. 105, I, 2.) 



(Syn. Ophiacantha spinulosa Miill. and Troschcl ; 0. hibernica 



Farran.) 



Disk closely covered with short stumps, also on the ventral 

 side ; neither scales nor radial shields distinct. Dorsal arm 

 plates rhomboidal or with convex outer edge, well separated. 

 Ventral plates Avith convex or slightly excavated outer edge, well 

 separated from base of arm. One rather large tentacle scale. 

 Six to eight slender, rather smooth arm spines, increasing in length 

 towards the dorsal side, the longest equalling 3-4 arm joints in 

 length. At base of arms the spines often join in the mid-dorsal 

 line. Three to four (or as many as 6) mouth papillae ; the outer 

 ones may be widened. Sometimes also some supplementary papillae 

 on apex of jaw or outside, at the adoral plates. Mouth shields 

 distinctly broader than long, with a very obtuse outer lobe. 

 Colour in life dark brownish. Arms ca. 3-5 times as long as 

 diameter of disk, which may be as much as 12 mm. 



It is a rather variable species, which is, however, easily 

 distinguished from the other species of the N.E. Atlantic. It is 

 known to be phosphorescent. 



In British seas this species has been found in the Faroe 

 Channel, 690-790 m. ("Porcupine"), and off S.W. Ireland, 

 1765 m. (" Helga ", recorded under the name of 0. hibernica 

 Farran). It is known elsewhere from the Arctic regions — it is 

 circumpolar — down to the Azores and Cape Verde, and on the 

 American east coast down to 33° N. In the Pacific it goes as 

 far south as Japan. Bathymetrical distribution ca. 10-4500 m. 



4. Ophiochondrus Lyman. 



Disk set with short spines or stumps, which do not conceal 

 the rounded, not imbricating, scales. Radial shields forming more 

 or less distinct elongate ribs. Dorsal arm plates divided. Mouth 

 papillae simple, spiniform. Tentacle scales indistinct or none. 



This diagnosis fits the European species, 0. armatus, but not the 

 genus Ophiochondrus proper. In fact this species, in the opinion 

 of the present author, does not properly belong to the genus 

 Ophiochondrus any more than to the genus Ophioplus, to which 

 it was at first referred. It ought rather to form a separate genus ; 

 but as this is not a fit place for estabhshing a new genus, it may 

 still be named Ophiochondrus here ; but it should not be forgotten 

 that it is, at least, very doubtful whether it is justly referred to 



