46 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



narrow and rounded distal border. The two or three following 

 plates are triangular, with an extremely obtuse proximal angle, much 

 rounded lateral angles, and a convex distal border; they are three 

 times as broad as long. Those following become less broad, and as- 

 sume a pentagonal shape with two short lateral borders. These 

 plates are separated beyond the second. 



The slightly projecting side arm plates bear six extremely short, 

 thick and cylindrical spines with the point blunted. The first ven- 

 tral spine is shorter than the segment, and the last scarcely equals a 

 segment and a half, except on the first segment, where its length is 

 slightly greater. On the first segment the two lateral columns of 

 spines come extremely close together in the dorsal median line of the 

 arm and are almost continuous, but beyond this they are widely sepa- 

 rated. The surface of the spines is simply rugose. 



All of the arm plates, as also the mouth plates, are covered with 

 little rounded granules which are very close together, though not 

 in contact. 



The single tentacle scale is small and conical with the point obtuse. 



Affinities and distinctive features. — OpMacomtha benigna is closely 

 related to O. brevispina Kcehler, which it recalls in the shortness of 

 the arm spines and in the breadth of the adoral plates, but it differs 

 from it in the form of the latter, which are still more broadened, by 

 the narrower and more elongated mouth papillae, by the rather closely 

 placed radial shields, by the absence of ribs on the dorsal surface of 

 the disk, and in the under arm plates which are at first remarkably 

 broadened; also in 0. hrevispina the armature of the dorsal surface 

 of the disk consists simply of fine and closely placed granules end- 

 ing in a few extremely short spinules. 



OPHIACANTHA COMPOSITA Kcehler. 



Plate 23, figs. 5, 6, 7 ; plate 93, fig. 4. 



See for bibliography : 

 Ophiacantha composita Kcehler ('07), p. 289; ('09), p. 188. 



Localities. — Albatross station 5119; Balayan Bay and Verde Island 

 Passage; Sombrero Island bearing S. 80° E., 35.03 kilometers (18.!) 

 miles) distant (lat. 13° 45' 05" N., long. 120° 30' 30" E.) ; 721 meters 

 (394 fathoms) ; January 21, 1908 ; gn. M., S. 



One specimen (Cat. No. 41134, U.S.N.M.). 



Albatross station 5601a; Gulf of Tomini, Celebes; Limbe Island 

 (NE. bearing N. 38.36 kilometers (20.7 miles) distant (lat. 1° 13' 

 10" N., long. 125° 17' 05" E.) ; 1,399 meters (765 fathoms) ; Novem- 

 ber 13, 1909 ; S., Glob. Ptr. 



One specimen in poor condition (Cat. No. 41132, U.S.N.M.). 



