OPHIUBANS OF THE PHILIPPINE AND ADJACENT WATERS. 385 



ders, forming with each other a very obtuse angle. The second plate 

 is quadrangular, broader than long, with the proximal border nar- 

 now; the distal border, which is very broad and convex, is itself 

 composed of two narrow sides united by a very obtuse angle. The 

 following plates become triangular, very much broader than long, 

 with a very obtuse proximal angle, very strongly divergent sides, and 

 a convex distal border. They are at first in contact beyond the disk, 

 becoming separated by a narroAv interval. The side arm plates carry 

 four spines on the first segments and only three on those following. 

 These spines are rather long, and their length increases from the 

 first ventral, which is half as long as the segment, to the dorsal, the 

 length of which equals almost that of the segment. These spines 

 are much flattened and rather strongly broadened in their mid-region, 

 with the tip rounded. 



The tentacle pores of the first pair are very large, and their proxi- 

 mal end is very close to the mouth ; they show on either border four 

 or five very large scales. The two pairs of pores following are still 

 fairly well developed ; the pores of the second pair have three scales 

 on the outer border and two on the inner ; the pores of the third pair 

 have two scales on each side. The pores of the fourth pair have 

 only a single scale on each border, and beyond this the pores, which 

 become very much smaller, show only a single proximal scale, very 

 much more reduced than the neighboring spine. 



The color of the specimen in alcohol is brownish white. 



Affinities and distinctive features. — Ophiura mitescens is espe- 

 cially close to O. flagellata (Lyman) and to O. palliata (Lyman) in 

 regard to the length of the arm spines and the characters of the dorsal 

 plates of the disk, which are very numerous, with poorly marked 

 outlines. The radial papillae are longer and less numerous than in 

 O. palUata, in which they are very fine and very pointed, and the 

 tentacle pores are continued less far than in that species; the arm 

 spines are broader and more flattened. In O. flagellata the radial 

 papillae are usually elongated and pointed, the arm spines are conical 

 and also very pointed, the dorsal surface of the arms is carinate, and 

 the under arm plates are shorter; furthermore, the arms of O. flagel- 

 lata are very much more broadened than those of 0. mitescens. The 

 new species differs still more from O. bathybia (H. L. Clark), from 

 the Bering Sea, in which the three arm spines are pointed and the 

 dorsal is larger than the two others ; the radial shields are extremely 

 elongated and narrow, the radial papillae are pointed, and spines 

 occur on both surfaces of the disk, structures which are entirely 

 lacking in O. mitescens. 



Ophiura mitescens also shows affinities with 0. fluctuans, which I 

 described above. It is easily distinguished from it by its very broad- 

 ened arm spines, maintaining almost the same width throughout 



55269— 22— Bull. 100—25 



