OPHIUROIDEA 229 



("Talisman"), 25° 49' N., 20° 12' W., 3015 m. ("Challenger"), also 

 known from the S. Atlantic and off Cape of Good Hope, 270-630 

 m. ; Ophiophycis Koehler, with the species 0. mirahilis Koehler, 

 found off the Azores, 1165 m. (" Princesse Alice ") ; Ophiotypa 

 Koehler, with the species 0. simplex Koehler, taken at 42° 19' N., 

 22° 36' W., 4000 m. (" Talisman "), and S.W. of the Cape Verde 

 Islands, 3655-4360 m. (" Talisman ", " Princesse Alice "), else- 

 where known from the Bay of Bengal, 3595 m. (" Investigator ") ; 

 OphiozoneUa Matsumoto, with two species (cf . below, p. 232). 



In the folloAving key the main characters of these genera are 

 given : 



Key to the genera of Ophiolepidce hnoivn from or likely to be 

 represented in the British seas. 



1. Second tentacle pore ^ outside the mouth edge, sometimes opening 



into the mouth slit, but always distinctly visible from the 



outside • ^ ' • • • • . • .2 



Second tentacle pore wholly inside the mouth edge, not visible 



from the outside . . . . . . .10 



2. Lateral plates of the innermost 2-5 arm-joints much widened 9 

 Lateral plates of the innermost arm- joints not widened . 3 



3. Radial shields not present ; dorsal side of disk covered almost 



exclusively by the primary plates, a very large central plate, 

 and 5 large radially situated plates, which touch the base of 

 the arms. Only one large, scale-like mouth papilla on each 

 side of jaw . . . . . Ophiotypa Koehler 



Radial shields present, the primary radial plates not touching 

 the base of arms ....... 4 



4. Dorsal arm plates absent.^ Disk covered almost exclusively 



by the large primary plates and radial shields.^ 



Aspidophiura Matsum. 



Dorsal arm plates present ; disk with more or less numerous 



small plates, among w^hich the primary plates may be more 



or less conspicuous ....... 5 



^ The second pair of tentacle (or tube -foot) pores is that corresponding 

 to the innermost, often rudimentary, ventral plate, which abuts against 

 the outer end of the mouth slit. 



^ The dorsal plates are absent in the N.E. Atlantic species of Aspido- 

 phiura ; in other species small dorsal plates are developed. 



^ Also in the young Homalophiura inornata the dorsal side of disk is 

 covered exclusively by the large primary plates and radial shields ; it is, 

 however, distinguished from Aspidophiura minuta by having dorsal arm 

 plates developed and, as a rule, the mouth shield divided by a longitu- 

 dinal line. Likewise, Amphiophiura convexa has the dorsal side of disk 

 covered almost exclusively by the primarj^ plates and radial shields ; it 

 is distinguished from Aspidophiura by its well - developed dorsal arm 

 plates and by the ventral plates being broadly in contact, these latter being 

 widely separated in Aspidophiura. 



