200 



bulletin: museum of comparative zoology. 



disk pale gray; under surface, side arm-plates and spines, whitish; 

 upper arm-plates irregularly white, dusky or deep gray, so the arms 

 look unevenly banded ; every upper arm-plate regardless of its ground- 

 color has the distal margin white and is crossed, immediately behind 

 this white margin by a very distinct band of deep gray; on plates 

 which are themselves deep gray, this band is almost black. The 

 color of the preserved specimen shows little change. 



The unusual character of this specimen was recognized when it was 

 collected, but diligent search failed to reveal another. It is quite 

 unlike any other West Indian brittle-star both in character of disk- 

 plates and in coloration. The distal oral papilla is so wide that it 

 would not be unnatural to include the species in Amphipholis but as 

 it does not quite equal the other two together, and as it is quite fan- 

 shaped in form, it is better to regard trychna as an Amphiodia. 



Amphiodia tymbara, sp. nov. 

 TVfi^apos = buried, in reference to the manner of life. 



Plate 2, fig. 6. 



HoJotype. — M. C. Z. 4,145. British West Indies: Tobago, Buccoo 

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

 half a dozen other species of amphiurans. Carnegie Expedition. 

 H. L. Clark coll. 



Disk, 8 mm. in diameter; arms at least 150 mm. long; the disk 

 has probably been recently regenerated and would perhaps ultimately 

 be a little larger but it is clear that the arms are fully 15 times the 

 diameter of the disk; two of the arms are regenerating from near the 

 base, one from the ninth the other from the twenty-fourth segment, 

 and they are not only shorter but much more slender than the normal 

 arms. Disk covered by a close coat of fine overlapping scales, about 

 15 series in each interradial area; no primary plates can be distin- 

 guished. Radial shields short, wide, and closely joined ; length about 

 one third of disk-radius; width about two thirds of length. Upper 

 arm-plates exceedingly wide and short, in contact for their full width ; 

 length about one fourth of breadth. Interbrachial areas below cov- 

 ered with rather coarse, overlapping scales. Oral shields (except 

 madreporite, which has length and breadth about equal) much longer 

 than wide, sharply pointed within; distal end blunt and distal sides 

 quite concave. Adoral plates rather large, a little swollen, much 



