CLARK: BRITTLE-STARS. 325 



plates long, very narrow, not much wider at inner ends where they 

 meet, than at outer ends where they are well separated. Oral plates 

 moderate with large oral pores. Tooth-papillae, rather few (12 ±) 

 and large. First under arm-plate small; outlines obscure but appar- 

 ently diamond-shaped, longer than wide; succeeding plates longer 

 than wide, at first squarish with rounded corners, but gradually the 

 proximal margin becomes strongly convex and the distal margin 

 equally concave; they are more or less completely in contact through- 

 out. Side arm -plates- moderate, not meeting either above or below; 

 each carries a series of 4 (at base of arm, 5) sharp, slender spines; 

 lowest, except on basal three or four segments, is in form of a big, 

 quadridentate hook, whose length (at middle of arm) equals width of 

 an under arm-plate; second spine is longer, blunt and thorny at tip; 

 third, much longer, less blunt, more thorny; fourth, longest, sharpest, 

 quite thorny, its length exceeding width of arm; fifth (when present) 

 shorter and smoother than fourth, pointed. Tentacle-scale, single, 

 minute, pointed. Color, dry specimen, deep purple (almost black), 

 with disk (especially on radial shields) microscopically and obscurely 

 variegated with a lighter tint; mouth-frames and under arm-plates, 

 white, in marked contrast; oral shields tinged udth purple; scat- 

 tered along upper surface of arms, frequently in longitudinal pairs 

 are conspicuous usually triangular spots of white, with apex pointing 

 distally; there are some 15-20 of these triangles on each arm; they 

 are not so large as the upper arm-plates and do not coincide with 

 them. 



Aside from its very striking coloration, the combination of char- 

 acters shown by the disk-covering, the upper and under arm-plates, 

 and the few arm-spines will serve to distinguish this species. 



OPHIOCHITONIDAE. 



Ophionereis olivacea. 

 H. L. Clark, 1901. Bull. U. S. F. C, 2, p. 248. 



While detained at Key West early in June, 1917, I visited a small 

 mangrove key about two miles north of the town. Here, in examin- 

 ing a handful of coralline Algae, I found a small brittle-star, which 

 although an Ophionereis, was neither 0. reticulata nor 0. squamulosa. 

 No similar specimen was found either near Key West nor at the Tortu- 



