CLARK: OPHIUROIDEA. 433 



wider than long; succeeding plates wider than long (until past middle 

 of arm) pentagonal or somewhat heptagonal, with a proximal angle 

 and slightly concave sides; they are separated throughout. Side 

 arm-plates large, low and wide, meeting both above and below; each 

 carries 4 blunt spines, of which the upper three are very flat and wide; 

 the two middle spines are chisel like at tip and in length are equal to 

 two or two and a half arm-segments; none of the spines are prickly 

 but under a lens, the margins are very finely serrate. Tentacle-scales 

 2, large and flat; they are situated on the side arm-plate but the inner 

 is very close to the under arm-plate; inner scale a trifle the longer 

 and distinctly the narrower, about equal in length to the lateral 

 margin of the under arm-plate; beyond the middle of the arm the 

 inner scale is nmch the smaller and is attached to the under arm-plate, 

 and still further out it disappears altogether. Color dull purplish 

 brown above, whitish beneath; arms conspicuously banded with 

 these two shades, the bands each 2-6 segments wide, but the whitish 

 bands always the narrower. 



Station 4642. Galapagos Islands: Hood Island, 4 miles southeast 

 of Ripple Point. 300 fms. Bott. temp. 48.6°. Brk. sh., glob. 



Station 4643. Galapagos Islands: Hood Island, 5 miles southwest 

 of Ripple Point. 100 fms. Bott. temp. 67.2°. Brk. sh., glob. 



Four specimens. 



This is a very well-marked species, not likely to be confused with 

 any other. While it resembles 0. noniiani in having four arm-spines, 

 the shape of those spines is very different ; the presence of two tentacle- 

 scales and the absence of granules on the upper arm-plates are addi- 

 tional differences of great importance. The superficial appearance 

 is much like that of some specimens of 0. cataleimmoida, but that 

 species has si.x or seven arm-spines and only a single tentacle-scale. 

 In tentacle-scales, under arm-plates, and mouth-parts, 0. quadri- 

 spina is very similar to 0. valenciennesi, but that species has seven or 

 eight arm-spines and spinules on the upper arm-plates. The con- 

 stancy in the number of arm-spines in 0. qundrispina is very striking 

 for there are no more than four on the basal arm-segments and there 

 are not fewer than four on the distal segments until near the tip of the 

 arm. It seems fair then to consider this one of the characteristic 

 endemic brittle-stars of the Galapagos Islands, very few of which are 

 as vet known. 



