OPHIUROIDEA 191 



Not as above . . . . . . . .19 



19. Disk covered with stumps with a crown of 7-8 thorns . 20 

 Disk covered with grain - hke stumps or with fine spinelets 



terminating simply or in three thorns . . , .22 



20. Outer (3rd) mouth papilla broad, the two inner simple, spiniform ; 



tentacle scale small, spiniform. (" Investigator " Ojph. PL VIII. 



66 ; " Siboga'\ Oph. PI. XXIII. 7) . O. composita Koehler 



All three mouth papillae simple, spiniform ; tentacle scale long, 



serrate (Fig. 107) 21 



21. Mouth papillae long and slender, spine -like. {" Challenger ", Oph. 



PL XXII. 1-4) O. nodosa 'Lym. 



Mouth papillae shorter, simply papilliform^ 



3. 0. aristata Koehler 



22. Disk with a dense covering of fine spinelets . . .23 

 Disk with grain-like stumps . . . . . .24 



23. Spinelets of disk ending in some (three or more) fine thorns ; 



dorsal arm plates cup -shaped , mouth shields with a pro- 

 minent outer lobe ; 6-8 arm spines (Fig. 105, 5-6) 



4, O. ahyssicola G. O. Sars 



Spinelets of disk simple ; dorsal arm plates triangular ; mouth 



shields with convex outer edge or with a very obtuse outer 



lobe ; 4 arm spines (Fig. 108) . . 5. O. densa Farran 



24. Arms 6 (rarely 7 or 5) ; mouth shields as long as broad (Fig. 105, 



7-9) ...... O. anomala G. O. Sars 



Arms 5 ; mouth shields broader than long (Fig. 105, 1-2) 



6. 0. bidentata (Retzius) 



1. Ojyhiacanth^ spectabilis G. 0. Sars. (Fig. 105, 3-4.) 



Disk covered with rather coarse spines, on the dorsal side 

 ca. 2 mm. long, on the ventral side shorter, more like granules. 

 Radial shields quite concealed. Dorsal arm plates triangular, 

 contiguous at base of arm, in larger specimens a good way out on 

 the arms. Ventral plates almost contiguous, not broader than 

 long, with convex outer edge. The proximal 2-3 pairs of pores 

 each wdth two tentacle scales, those beyond with only one large 

 and broad tentacle scale. Arm spines 8, farther out 6-5 ; they 

 are smooth, compressed, increasing somewhat in length toAvards 

 the dorsal side, the uppermost ones being as long as 2-3 arm 

 segments ; they almost join in the dorsal mid-line for a good 

 distance out on the arms. Mouth papillae usually 4 on each side 

 of jaw, in larger specimens more, as many as 8. Mouth shields 

 rounded, prolonged outwards, provided with some short spines 



^ O. nodosa and aristata evidently are very closely related and perhaps 

 will prove to be identical. 



