NORTH PACIFIC OPHIURANS IN NATIONAL MUSEUM CLARK. 149 



Locality. Albatross station 3702, off Seno Umi, Honshu Island, 

 Japan, 31 to 41 fathoms, volcanic mud, sand, rocks, 1 specimen. 



Type. Cut. No. 25628, U.S.N.M., from station 3702. 



It is to be regretted that only a single, badly broken specimen rep- 

 resents this remarkable species in the collection. It combines such 

 an unusually large number of arm spines with such peculiar Tipper 

 arm plates and unusually naked disk that it is really quite unique. 



AMPHIURA TRACHYDISCA, new species, a 



Disk 13 mm. in diameter; arms probably from 125 to 150 mm. in 

 length. Disk covered with very numerous scales, the larger of which 

 bear hemispherical or more elevated swellings, which on the inter- 

 radial margins become somewhat cylindrical, and may be nearly half 

 a millimeter long. Radial shields about twice as long as wide, sepa- 

 rated or just in contact distally. Upper^arm plates about twice as 



FIG. f.o. AMPHIURA TRACHYDISCA. X 4. a, FROM ABOVE; 6, FROM BELOW; c, SIDE VIEW OF TWO ARM 



JOINTS NEAR DISK. 



wide as long, rather broadly in contact ; the shape may be considered 

 either a more or less angular transverse oval, or a very wide, short 

 hexagon with rounded angles; the first two or three are smaller than 

 those which follow. Interbrachial spaces below covered by a very 

 close coat of small and minute scales, only the larger, marginal ones 

 bearing the characteristic swellings. Oral shields broadly oval, 

 about as wide as long, somewhat abruptly narrowed distally. Adoral 

 plates roughly triangular, with the longest side adjoining the oral 

 shield and deeply concave. Oral papillae, two on a side, one round 

 and thick at apex of jaw, and one stout, acute and spine-like at outer 

 corner of mouth angle ; tentacle scale of first oral pore also large and 

 spine-like. Genital slits short and inconspicuous. First under arm 



, signifying rough, and OCOKOC, signifying disk, in reference to the remark- 

 ably rough disk. 



