CLARK: BRITTLE-STARS. 289 



planispina a sufficiently variable species to include A. rhabdota as 

 well as the larger Tortugas specimen here referred to it. But until 

 such material is available, it seems better to distinguish the two forms. 



Amphiodl^ trychna, sp. nov. 



rpvxvos = rough, in reference to the character of the disk. 



Plate 3, fig. 1-3. 



Holotype. — M. C. Z. 4,144. British West Indies: Tobago, Buccoo 

 Bay, Sandy Point, April, 1916, in sandy mud in 2-3 ft. of water, in 

 company with half a dozen other species of amphiurans. Carnegie 

 Expedition. H. L. Clark coll. 



Disk, 3.5 mm. in diameter; arms 30-35 mm. long. Disk covered 

 with a coat of coarse, thick scales; only about 5 series in each inter- 

 radial area; these scales are swollen on the distal margin and on the 

 larger ones are additional knobs; the whole surface of the disk is 

 thus quite rough and irregular. Radial shields, relatively large, about 

 equal to half disk-radius and twice as long as wide, closely joined 

 along their straight adradial edges; except along the abradial margins 

 they are sculptured and rough. Upper arm-plates fan-shaped or 

 triangular but, except at very tip of arm, sufficiently overlapped so 

 that the proximal angle is considerably truncate; they are wider than 

 long, the distal margin is slightly convex and the distal angles are 

 rounded. Interbrachial areas below covered with coarse scales, 

 swollen on the distal margin. Oral shields, diamond-shape, longer 

 than wide (except madreporite), rough and slightly swollen. Adoral 

 plates, very large, swollen, not much longer than their distal width, 

 narrower within where they are broadly in contact; radially they are 

 widely separated by first under arm-plate. Oral plates small, but 

 evidently swollen proximally. Oral papillae 3 on each side, thick, 

 slightly swollen at tip; distal one widest, fan-shaped, not so wide as 

 the other two together. First under arm-plate rather large, triangular, 

 distal margin conspicuously swollen; succeeding four or five pen- 

 tagonal, with proximal angle more or less truncate, as wide as long or 

 wider, more or less conspicuously swollen distally; succeeding plates 

 squarish, as long as wide or longer, broadly in contact, not swollen. 

 Side arm-plates, rather small, not meeting either above or below; 

 each bears 3 subequal, truncate, flattened spines, as long as the seg- 

 ment. Tentacle-scales, 2, large and conspicuous. Color, in life. 



