218 



BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



widely separated. Upper arm plates more or less rhombic, or tri- 

 angular with distal margin convex or straight, wider than long, only 

 a few of the basal ones in contact; distal margin of some basal ones 

 carrying granules as in normani. Interbrachial spaces below with a 

 sparse granulation. Genital slits very large. Oral shield tetragonal, 

 very short and wide. Adoral plates rather large, proximal to oral 

 shield, meeting broadly within, slightl}^ curved. Oral papillae 

 rather large, three on a side and often one at apex of jaw, subeqiial 

 or the distal one largest. First under arm plate small, wider than 

 long; succeeding plates heptagonal, hexagonal, or pentagonal, 

 according to the truncation or rounding of the proximal and distal 





Fig. 100.— Ophiacantha cataleimmoida. x 3. a, from above; b, from below; c, side view of two 



ARM JOINTS NEAR DISK. 



angles, wider than long, all but the first two distinctly separated. 

 Side arm plates moderate, in contact both above and below; each 

 plate carries six or seven straight, smooth spines, of which the next 

 to the uppermost is longest and may exceed three joints; rows of 

 spines not approximate dorsally. Tentacle scale single, very large, 

 flat, rounded, and more or less distinctly curved outward around the 

 base of the lowest arm spine. Color (dried from alcohol), quite vari- 

 able, ranging from deep purplish-brown to light yellowish-brown or 

 even almost white; dark specimens sometimes have the disk mottled 

 with lighter; the rubbing off of the disk granules, with its consequent 



