266 bulletin: museum of comparative zoology. 



Disk 3 mm. in diameter; arms six, 15 mm. long. Disk covered by 

 a close coat of thin, overlapping scales, many (but by no means, all) of 

 which bear thick, cylindrical, rough-pointed spinelets; there is never 

 more than one spinelet to a scale; the spinelets are rather longer than 

 the diameter of the scale but are seldom equal to twice that length; 

 altogether there are about 100-125 spinelets on the disk. Radial 

 shields can be detected only with difficulty; they are widely sepa- 

 rated and the visible portion, which is triangular, is little larger than 

 a disk-scale. Upper arm-plates with proximal half V-shaped and 

 distal half semicircular; they are about as wide as long, and are barely 

 in contact proximally but become more and more separated distally. 

 Interbrachial areas below covered by a coat of thin scales, like those 

 on the disk, but very few bear spinelets and they are near margin. 

 Genital slits relatively large. Oral shields shaped much like the upper 

 arm-plates but the distal margin is not so evenly rounded and the 

 proximal sides are not quite so straight. Adoral plates rather long, 

 meeting interradially; width of distal end about half length, and 

 proximal end about half as wide as distal. Oral plates relatively 

 large and distinct, triangular, each with 4 oral papillae of which the 

 distalmost is longest and widest and the proximalmost is thickest; 

 no oral papillae on adoral plate. At tip of jaw are 2 or 3 tooth- 

 papillae similar to proximalmost oral papillae but they may be both 

 longer and stouter. First under arm-plate small, nearly triangular, 

 with the blunt distal angle, separating the adoral plates; second plate 

 shield-shaped, a trifle wider than long, with rather sharp lateral angles; 

 succeeding plates, longer than wide, pentagonal with distal angles 

 rounded and lateral margins slightly concave; they are in contact, 

 though barely so, beyond middle of arm. Side arm-plates rather 

 large, the distal margins thickened as a moderately conspicuous spine- 

 bearing ridge; each plate carries 3 (basally there may be 4) straight, 

 bluntly pointed, nearly smooth, hollow arm-spines; uppermost 

 (except when 4 are present) longest, equal to an arm-segment and a 

 half. Tentacle-scale single, large, flat and only bluntly pointed. 

 Color yellow-brown; disk paler; there are indefinite deep dusky 

 bands at intervals of two or three segments on basal half of arm; 

 distally there are no markings. 



This little specimen was the only representative of its family found 

 at the Tortugas. It is well-characterized by the number of arms, the 

 number and appearance of the arm-spines, the oral and tooth-papillae 

 and the upper arm-plates. The color has undergone little change in 

 preservation. Its nearest relative would seem to be 0. ophiactoides 



