74 



BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



These specimens vary in disk diameter from 3 to 8 mm. They 

 show considerable diversity in height and form of disk, and in the 

 shape and length of the arm-comb papilla, but even the smallest 

 specimens are at once distinguishable from young nodosa by the 

 arm spines. 



OPHIURA (EDIPLAX, new species.o 



Disk 5 mm. in diameter; arms about 12 mm. long. Disk covered 

 by twenty-one plates, a centro-dorsal, five radial, five interradial, 

 and five pairs of radial shields; all disk scales more or less tumid 

 though the radial shields are least so. Radial shields squarish, 

 joined for most of their length. Upper arm plates thick and swollen, 



somewhat pentagonal (be- 

 coming tetragonal and finally 

 trigonal), but with more or 

 less rounded angles; all 

 but basal ones longer than 

 wide, first three, four, or five 

 n contact. Interbrachial 

 spaces below covered almost 

 wholly by the oral shields, 

 distal to which a large mar- 

 ginal plate and the two geni- 

 tal scales may be seen; a 

 couple of small angular plates 

 often lie between oral shields 

 and marginal plate. Oral 

 shields longer than wide, 

 rounded without, pointed 

 within. Adoral plates very 

 large, twice as long as wide; 

 C oral plates somewhat smaller 



FIG. 21. OPHIURA (EDIPLAX. X10. a, FROM ABOVE; 6, FROM but quite indistinct. Oral 



BELOW; C, SIDE VIEW OF THREE ARM JOINTS NEAR DISK. '11 ' "U -C 



papillae minute, about five 



on a side. Genital scales very stout, with a marginal series of about 

 a dozen short, blunt papillae, which form the inconspicuous arm 

 comb when seen from above. Basal under arm plates somewhat 

 hexagonal or pentagonal, and though the plates rapidly diminish in 

 size, they undergo little change of form, except that they become 

 wider than long distally, while at first they are decidedly longer than 

 wide. Side arm plates somewhat swollen, at first higher than long, 

 but rapidly becoming longer than high, in contact except at base of 

 arm; each plate carries one small arm spine, high up on the distal 



), signifying to swell, and x\a, signifying a plate, in reference to the swollen 

 disk and upper arm plates. 



