OPHITJRANS OF THE PHILIPPINE AND ADJACENT WATERS. 213 



then the length increases rapidly, and the three following almost 

 equal three segments and a half; the last dorsal spine is generally 

 shorter than the preceding. The lateral spines broaden toward the 

 tip, at the same time becoming samewhat flattened, but the dorsal 

 spines does not broaden and ends in a point. All are perfectly 

 transparent and furnished with strong pointed and closely placed 

 denticulations. The first ventral spine beyond the tenth segment 

 is converted into a somewhat elongated hook with generally four 

 branches the length and thickness of which increase from the first 

 to the last (pi. 97, fig. 45). 



The tentacle scale is small, oval, with the tip rounded, scarcely 

 longer than broad (fig. 4<?). 



The general coloration is red. The dorsal surface of the disk is 

 rather dark, of a quite uniform slightly brownish red. A white line 

 runs along the median dorsal line of the arms, narrowing slightly 

 toward the middle of each upper arm plate and broadening toward 

 the distal border. On either side runs a very narrow red line which 

 follows the outlines of the white band ; small red longitudinal striae 

 are seen on the pink background of the upper arm plates outside of 

 this median line. The ventral surface of the disk is dark brown, but 

 the spines which it bears are roseate. The ventral surface of the 

 arms is pink ; a white band runs throughout the whole length of the 

 ventral median line and it is bounded on each side by an extremely 

 narrow scarcely darker line which shows at the plane of the border 

 of each segment a small darker dot. The spines are transparent, 

 though slightly roseate. 



Affinitities and distinctive features. — Ophiothrix bellax belongs to 

 the section of Ophiothrix in which the radial shields are covered 

 and the arms are very long, and it approaches O. puncto-limbata 

 Martens, O. longipeda (Lamarck), O. hirsuta Miiller and Troschel, 

 O. belli Doderlein, O. obtusa Kcehler, and 0. expedita Kcehler. It 

 is distinguished from O. belli by the much longer arm spines which 

 are denticulated throughout their whole length, broadening grad- 

 ually and not abruptly in their distal half ; the covering of the disk 

 consists of small short spines mixed with club spines, and the radial 

 shields are more covered than in O. belli. It differs from O. obtusa, 

 in which the surface of the disk is simply covered with little rugose 

 granules and in which the arms are shorter. In the form of the 

 upper arm plates O. bellax is sharply distinguished from O. hirsuta, 

 O. longipeda, and O. puncto-limbata. Furthermore the coloration 

 is entirely different in the species which I have just mentioned. 

 Only 0. expedita has a coloration comparable to that of O. bellax; 

 it is, however, a little darker and verging toward brown ; but the form 

 of the radial shields is very different and the arms of O. expedita 

 show on their dorsal surface three very characteristic white lines. 



