OPHIUROIDEA 235 



4. The two innermost ventral plates broadly contiguous. (" Chal- 



letiger " Oph. PL V. 7-9 ; " Monaco'', xxxiv. PI. XXVII. 



7-8 ; " O. mwidata ") . . . . O. irrorata (Lym.) 



All the ventral plates widely separated . 5. O. rohusta Ayres 



5. Second tentacle pore opening into the mouth slit ; proximal 



pores with several tentacle scales ..... 6 



Second tentacle pore not opening into the mouth slit ; only 



one tentacle scale, also at the proximal pores ^ . . 12 



6. Radial shields contiguous throughout half their length ; primary 



plates very distinct. (" Talisman " Oph. PI. XVIII. 9-10) 



O. imprudens (Koehler) 



Radial shields separated or, at most, contiguous at their distal 



ends .......... 7 



7. The innermost 4-5 ventral plates broadly contiguous, nearly 



quadrangular. (" Monaco ", xxxiv. PL XXV. 3-5) 



O. concreta (Koehler) 



The innermost ventral plates separated or, if contiguous, not 



quadrangular, but much broader than long ... 8 



8. Scales of disk very small, scarcely visible through the rather 



thick skin ; or central part of disk wholly naked. Arm spines 

 3, longer than an arm joint. (" Challenger " Oph. PL IV. 



16-18) 0. flagellata {Lym.) 



Scales of disk distinct, not concealed by the skin . . 9 



9. The 3 arm spines placed at equal distance from one another 10 

 The arm spines placed at unequal distance from one another ; 



two or three of them close together at the lower end of lateral 

 plate, close to tentacle pore, one separate at upper end of 

 lateral plate, close to the dorsal plate . . . .11 



10. Innermost dorsal plate heart-shaped ; upper arm spine about 



half the length of arm joint . . 3. O. albida Forbes 



Innermost dorsal plate not heart-shaped ; upper arm spine 



longer than an arm joint . . . 2. O. Sarsi Liitken 



11. Radial shields usually contiguous at distal end; upper arm 



spine distinctly longer than the low^er ones 



4. O. Ljungmani (Lj^m.) 

 Radial shields wholly separate ; upper arm spine scarcely longer 

 than lower ones. (" Challenger " Oph. PL IV. 1-3.) 



O. lepida (Lym.) 



12. Dorsal arm plates broadly in contact nearly throughout the arm, 



quadrangular, roof -shaped. The smaller scales of disk 

 arranged in regular circles around the primaries . .13 



1 In one of the species put under this group, 0. Grubei, the character of 

 the second pore not opening into the mouth slit is less distinct ; but then 

 it is distinguished from the species within the group 6 by having only one 

 tentacle scale on the proximal pores, at least from the seventh pair, i.e. the 

 second pair on the arm. 



