190 ECHINODERMS OF THE BRITISH ISLES 



6. Arm spines 11. {"Challenger'' Oph. PI. XXV. 11-12) 



O. rosea Lyman 

 Arm spines 6-7 ........ 7 



7. Radial shields forming elevated ridges; disk with granular 



stumps. (" Monaco ", xxxiv. PL XXIX. 3-4) O. veterna Koehler 

 Radial shields not forming elevated ridges . . .8 



8. Disk with granules and spines. {" BlaJce'' Oph. PI. V. 70-72) 



O. Bairdi Lyman 

 Disk with granular stumps 6. O. bidentata (Retz.) {pro parte) 



9. Radial shields forming elevated ridges . . . .10 

 Radial shields not forming elevated ridges . . .13 



10. Disk naked, radial ridges covered with stumps ; 7-8 arm spines. 



{''Monaco ", xii. PI. VIII. 37-38) . O. setosa Mull, and Trosch. 

 The whole disk covered with short stumps or spines . .11 



11. Some slender spines scattered among the stumps on disk and 



radial shields ; 6 arm spines ^ . .0. Smitti Ljungm. 



No spines on disk, only a uniform covering of small stumps . 12 



12. Ventral side of disk without stumps, the scales distinct; five 



short arm spines ; outer mouth papilla not much enlarged, 

 {''Monaco'', xii. PI. VIII. 43, IX. 44) 0. hrevispina Koehler 

 Ventral side of disk with stumps ; 7-8 arm spines ; outer mouth 

 papilla broad, scale-like. {Bull. U.S. Nat. Mus. 84, PI. IX. 

 1-2, O. meridionalis) . . .0. mesembria H. L. Clark 



13. Disk with sparse, rather coarse spinelets, which do not conceal 



the scales ......... 14 



Disk with short stumps or grains or a close coat of fine spinelets, 

 which conceal the scales . . . . . .15 



14. Mouth papillae small conical. (" Talisman", PI. XX. 31-32) 



O. decipiens Koehler 

 Mouth papillae large, flattened (Fig. 106) 2. 0. crassidens Verrill 



15. Radial shields naked and distinct, though small . .16 

 Radial shields covered, at most outer end distinguishable . 1 7 



16. Ventral plates contiguous ; tentacle scale about as long as the 



ventral plate, slender, serrate ; mouth shield longer than 

 broad, almost rectangular. {"Talisman" , PI. XX. 36-38) 



O. notata Koehler 



Ventral plates separated ; tentacle scale broad, not as long as 



ventral plate ; mouth shield about as broad as long, with an 



outer lobe. (" Talisman ", PL XX. 33-35) 0. parcita Koehler 



17. Arm plates with fine, but distinct, parallel transverse lines. 



{"Monaco", xxxiv. PL XXV. 6-8) . O. lineata Koehler 



No transverse lines on arm plates . . . . .18 



18. The outer (4th) mouth papilla very broad and scale-like, meeting 



that of the opposite side so as to close the outer end of mouth 

 slit. Some granules on middle of jaw. Disk with smooth 

 granules. {"Monaco ", xxxiv. PL XXVII. 9-10) 



O. opercularis (Koehler) 



^ This species has never been figured. 



