OPIIIOTIIUIX. 



-Do 



OPniOTIIRIX Mull. & Trosch. 



Tyi'E oi' Tiiii Genus, 0. rosula Forbes. 



Disk with thorny grains, very short sjoines crowned with thorns, or 

 spines with thorns at the sides and toi). Eadial shields larire, triant'u- 

 lar swelhngs, each bounded on its two inner sides by ridges in the skin 

 of the back. Tooth-papilUv\ Teeth. No mouth-papilla?. Spines nu- 

 merous (often three times as long as the joints), flattened, glassy, 

 thorny, having a central tube with slender side tubes from it. A 

 small, spine-like tentacle-scale. No radial scales. The base of the jaw 

 pierced with a hole, from a want of perfect union between the two 

 pieces of the mouth-frames. Interbrachial spaces swelled out like 

 lobes. Two genital slits beginning outside the mouth-shields. Outer 

 arm-joints with hooks. 



GROUPING OF SPECIES HEREIN DESCRIBED. 



Disk closely beset with stout, longer and shorter spines, 



Disk with long, slender spines, 



Disk usually beset with short, forked, and with long, slender spines, 



Disk with fine, thorny grains ; upper arm-plates regularly hexagonal. 

 Disk and radial shields closely beset with spiny cylinders ; thorny grains ) 



on upper ann-jilates, j 



Disk scaled, and sparsely beset with thorny grains, 



Disk beset w^ith thorny stumps ; radial shields closely covered with grains. 

 Disk and radial sluelds as in the last; upper arm-plates regularly angu-) 



lar ; arms very long, j 



0. rosula. 

 0. Orstedii. 

 0.,Suensonii. 

 0. marfnijica, 

 0. virgata. 

 0. angulata. 

 0. violacea. 

 0. spiculata. 

 0. dumosa. 

 0. lineata. 



0. demessa. 



0. propinqua. 

 0. Cheneyi. 



0. longipeda. 



20 



