236 BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



longation of the under arm plates, or whether its floor is formed 

 simply of connective tissue, is not clear from an external examina- 

 tion of the dry specimen. Side arm plates very short and separated 

 from each other by an area of bare, uncalcified skin, as wide as them- 

 selves; each plate carries a conspicuous vertical ridge on which are 

 borne seven or eight arm spines; of these the four or five uppermost 

 are stout, smooth, and blunt, the two middle ones longest and nearly 

 equaling two joints; the three or four lowest spines are very much 

 smaller than the upper ones, are rough or hooked at the tip, and 

 practically serve as tentacle-scales (see fig. lllc). Tentacle pores 

 very large ; first one usually with no .tentacle scale, but sometimes 

 with a small one ; next three pairs of pores with a single well-marked 

 scale on the side arm plate but not on the spine-bearing ridge; 

 beyond the fourth pair of pores, the tentacle scales are replaced by 

 the lowest arm spines. Color (dried from alcohol), disk deep brown, 

 finely speckled with white and black; radial shields and adjoining 

 scales yellowish- white; arms light drab; oral surface yellowish- white, 

 except for the brown interbrachial spaces. 



Locality. Albatross station 4980, off eastern Japan, lat. 34 9' N.; 

 long. 137 55' E., 507 fathoms, brown mud, fine sand, foraminifera, 

 bottom temperature 39, 4 specimens. 



Type. Cat. No. 25549 U.S.N.M., from station 4980. 



This remarkable ophiuran is almost certainly entitled to be the 

 type of a new genus, the large amount of uncalcified skin and the 

 peculiar condition of arm spines and tentacle scales furnishing good 

 generic characters. But until Ophiacantha is more carefully revised 

 and the limits of its component genera better understood, I think 

 this species may well rest therein. It is not likely to be mistaken 

 for any of the now known species of that genus. 



OPHIACANTHA MACRARTHRA, new species.a 



Disk 2 mm. in diameter; arms about 7 mm. long. Disk covered 

 with few coarse scales, upon which are borne some minute stumps, 

 more or less elongated, conical, and with several terminal teeth. 

 Radial shields hardly distinguishable from the other disk scales, 

 closely joined. Upper arm plates minute, triangular or rhombic, 

 widely separated. Interbrachial spaces below like disk above. 

 Genital slits very large. Oral shield large, wider than long, dis tally 

 rounded but with a proximal angle. Adoral plates large, L-shaped, 

 meeting within and separating the oral shield from the side arm 

 plate; oral plates rather large. Oral papillse three on a side and one 

 at apex of jaw; latter much the largest, broad, flat, pointed; outer- 



a MaKpdf, signifying long, and dpdpov, signifying joint, in reference to the very long 

 arm joints. 



