OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 49 



arm outward by an interval greater than their own length which is 

 entirely occupied by the side arm plates. 



The first under arm plate is rather large, triangular, with an 

 obtuse and rounded distal angle and similarly slightly rounded sides. 

 The second is large, pentagonal, very much broader than long, with 

 a very obtuse proximal angle bordered by slightly concave sides, the 

 lateral borders excavated by the tentacle scale, and a very broad and 

 convex distal side. This plate is not quite in contact with the first. 

 The following plates become smaller, though remaining pentagonal, 

 but the proximal angle finally becomes so obtuse that its two sides 

 are almost the prolongation of each other, and the lateral borders 

 are almost straight. These plates are always broader than long, and 

 they are widely separated. 



The side arm plates, which are strongly projecting, carry seven 

 extremely fine elongated, pointed, vitreous spines, which are provided 

 with rather closely placed small denticulations. The length increases 

 from the first ventral spine, the length of which exceeds that of the 

 segment, to the second from the dorsal end of which the length 

 reaches almost three segments ; the last dorsal spine is a little smaller. 

 The two lateral columns of spines come very close together in the 

 median dorsal line on the first arm segments. 



The single tentacle scale is rather large, but narrow, spiniform, 

 and pointed, and it reaches almost the length of the corresponding 

 under arm plate. 



The color of the dorsal surface of the disk is a rather light brown ; 

 the arms are similar in color with indications of spaced white rings ; 

 the ventral surface is almost white. 



I have mentioned above that the Siboga specimen was found at a 

 littoral station (36 meters, or 19.5 fathoms), and therefore at a 

 depth less than the Albatross specimen, which comes from a coastal 

 station in 232 meters (127 fathoms). This latter still shows very 

 clear traces of a coloration indicating that it lived at a relatively 

 slight depth to which some luminous radiations must have pene- 

 trated. 



OPHIACANTHA DALLASH Duncan. 



Plate 16, figs. 1-3. 



Ophiacantha dallasii Duncan ('78), p. 471, pi. 11. figs. 25-27.— Doderlei* 

 ('96), p. 291, pi. 14, fig. 3: pi. 16, fig. 12.— Pfeffer ('00), p. 83.— Kcehler 

 ('05), p. 55.— H. L. Clark ('15), p. 198.— Matsumoto ('17), p. 113. 



Localities. — Albatross station 5135; vicinity of Jolo; Jolo Light 

 bearing S. 46° W., 22.07 kilometers (11.91 miles) distant (lat. 6° 11/ 

 50" N., long. 121° 08' 20" E.) ; 294 meters (161 fathoms) ; Febru- 

 ary 7, 1908 ; f ne. co. S. 



One specimen (Cat. No. 40925, U.S.N.M.). 



55269— 22— Bui. 100 4 



