CLARK: BRITTLE-STARS. 313 



M. C. Z. collection, taken by the Blake, and said to be from off St. 

 Vincent in 124 fms., is exactly like ordinary shallow-water specimens. 

 It was perhaps not actually dredged at so great a depth. 



The diversity shown by this species extends to all the characters 

 by which species in the genus are to be distinguished. The covering 

 of the disk varies greatly ; in typical specimens there is a more or less 

 dense coat of minute bifid or trifid stumps, which covers to some 

 extent at least the radial shields, but it is very common to find longer, 

 acute, rough spinelets scattered among the stumps and frequently 

 the spinelets are very numerous ; in extreme cases there are no stumps 

 at all. Often the radial shields are perfectly bare and they may be 

 also very large and sharply set off from the disk-covering. Even the 

 upper and under arm-plates and also the oral shields show no con- 

 stancy to any characteristic form. The arm-spines are usually 

 rough and pointed, but the upper ones are often more or less markedly 

 flattened and sometimes, when not flattened, they are almost smooth. 

 In coloration, the diversity is so great that it is difficult to decide 

 what is the typical form but there is commonly a white longitudinal 

 stripe on the upper side of the arm, which is quite characteristic. 

 This stripe is, however, frequently wanting and such specimens can 

 then be assigned to 0. angulata only by becoming satisfied that they 

 are not 0. hrachyaciis, 0. lineata, 0. orsiedii, 0. pallida, or 0. suensonii! 



To bring some sort of order into this heterogeneous assemblage, 

 I distinguish some of the recognizable forms as varieties and desig- 

 nate six of these, giving them names expressive of their distinctive 

 character. 



Key to the West Indian species and varieties. 



a Arms beautifully and regularly cross-banded with dark or colored lines 

 which are bounded on each side with white or yellow. 



b Ground color some shade of green, purple, or brown orstedii 



b' Ground color bright orange-chrome orstedii var. lutea 



a' Arms not so cross-banded. 



6 A distinct, median, colored or black line on upper surface of arms, 

 c No spines or spinelets on disk but only very low, rough granules 



lineata 

 c' Disk with spines or spinelets. 



d Radial shields very large and perfectly bare, the narrow areas 



between with few, long, slender spines suensonii 



d' Radial shields moderate or small, at least the inner ends with 

 minute spinelets. 



