OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 379 



as long. On the succeeding plates the length increases rather rapidly 

 and the plates become as long as broad, then longer than broad in the 

 distal half of the arms. These plates are always widely in contact, 

 with the proximal border narrower than the distal, which is slightly 

 convex, and with the lateral angles very pronounced. 



The first under arm plate is large, triangular, broader than long, 

 or simply oval and transversely broadened. The two following are 

 quadrangular, with the proximal border very much narrower than 

 the distal, which is much broadened; they are very much broader than 

 long, and broadly in contact. The proximal border narrows very 

 much on the fourth plate, and beyond the fifth it is replaced by an 

 obtuse angle. The following plates become very much shorter and 

 very broad, and they are separated by a space which becomes greater 

 and greater; their distal border is sinuous, and shows a small median 

 lobe. 



The side arm plates bear three spines which are rather broad at 

 the base, flattened, and very pointed, of which the length increases 

 progressively from the first to the third; the first is shorter than 

 the segment, the second almost equals the segment, and the third 

 is slightly longer (fig. 5). 



The tentacle pores are very large and provided with numerous 

 scales. Those of the first pair carry about six on either side; those 

 of the second, third, and fourth pairs also have six on their proxi- 

 mal side, and four, and then three, on their distal side; those of the 

 fifth pair have five proximal scales and three distal ; then the num- 

 ber of the scales decreases little by little, the distal scales disap- 

 pearing rather rapidly while the proximal scales fall to three in 

 number and then to two. 



Affinities and distinctive features. — Ophiura fluctuans is very close 

 to O. flagellata, and it may be asked whether these are not really 

 young specimens of this latter species, but such a supposition would 

 be quite erroneous, as a comparison of specimens of the same size 

 belonging to both species shows. I have given on plate 85, figure 6, 

 the dorsal surface of 0. flagellata, in which the diameter of the disk 

 is 18 mm.; it is consequently very nearly of the same size as the 

 larger specimen of O. fiuctucms which I have just described and of 

 which the dorsal surface is represented in figure 2 of the same plate. 

 By comparing these two photographs the differences in the relative 

 dimensions of the arms and of the disk are at once seen; the arms 

 are very broad in O. flagettata, while they are very narrow in O. 

 fluctuans; the relation between the width of the arms and the diam- 

 eter of the disk is 1:3.3 in the first species and 1:4.2 to 1:4.3 in 

 the second. The upper arm plates, which are four times as broad 

 as long on the 10 or 15 proximal arm segments in O. flagellata, are 

 scarcely half again as broad as long on the six proximal segments 



