﻿OPHIOTHRIX. 153 



OPHIOTHEIX MiJLL. & Trosch. 



Type of tue Gends, 0. rosula Forbes. 



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

 spines with thorns at the sides and top. Eadial shields large, triangu- 

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

 of the back. Tooth-papillaj. Teeth. No mouth-papillas. 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 OP SPECIES HEREIN DESCRIBED. 



Disk closely beset with stout, longer and shorter spines, 0. rosula. 



r 0. Orstedii. 



. Jo. Suensonii. 



Disk with long, slender spines, , i /^ -j? 



=■' ^ ' C. magmjica. 



L 0. virgata. 

 C 0. angulata. 

 J 0. violacea. 

 Disk usually beset with short, forked, and with long, slender spines, '] Q 'if 



L 0. dumosa. 

 Disk with fine, thorny grains ; upper arm-plates regularly hexagonal, 0. lineata. 



Disk and radial shields closely beset with spiny cylinders ; thorny grains } (-> j 



on upper arm-plates, j 



Disk scaled, and sparsely beset with thorny grains, 0. propinqua. 



Disk beset with thorny stumps ; radial shields closely covered with grains, 0. Cheneyi. 

 Disk and radial shields as in the last ; upper arm-plates regularly angu- \ q i^^gi^^^^^ 



lar ; arms very long, ) 



