OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 201 



The adoral plates are rather short and very narrow in their proximal 

 portion where they are almost in contact in the median interradial 

 line; outwardly they broaden very greatly and separate the mouth 

 shield from the first side arm plate. The oral plates are small, half 

 again as high as broad. The mouth papillae, three in number, are 

 arranged as in the genus Amphiura: the proximal papilla is very 

 thick and cubical in form, the second, situated on a higher level, is 

 conical and pointed; the outermost papilla, borne by the adoral plate, 

 is broad, thick, and conical. 



The upper arm plates are small, rounded, as long as broad, or a 

 little longer than broad, with an almost straight proximal border; 

 the sides are rounded and convex, and they are united over a simi- 

 larly rounded distal border. They are all in contact. 



The first under arm plate is very narrow and crowded in between 

 the neighboring adoral plates, but it is rather elongated. The fol- 

 lowing plates are rectangular, almost as long as broad, and rather 

 small, with a straight or slightly convex proximal border, a distal 

 border very distinctly concave and excavated in the middle, and 

 straight sides ; they are all in contact. 



The very strongly projecting side arm plates are also much devel- 

 oped, and they cover a large part of the dorsal and ventral surfaces 

 of the arms. They bear ten arm spines, which are conical and sub- 

 equal with the point blunted, and almost equal the arm segments in 

 length. The lateral spines — that is, those between the second and 

 fifth, inclusive — often have their tip slightly broadened and provided 

 with two or three small conical teeth, which may be equal or un- 

 equal ; it is rarely that one of these last is developed more than the 

 others, forming a small slightly incurved hook directed toward the 

 distal extremity of the arm (pi. 96, fig. 11). 



The tentacle pores are without scales. 



The color of the specimen in alcohol is grayish. 



Affinities and distinctive features. — Ophiocentrus vexator is very 

 close to O. verticillatus (Doderlein) and one might suppose that it 

 is only a simple variety of it, but the conical arm spines, which are 

 not at all flattened, and are terminated by two or three teeth, of 

 which one may form a little hook at the tip, are so different from 

 the flattened spines broadened in the middle with the tip rounded 

 which Doderlein has described that it seems to me impossible to unite 

 the two forms. 



My description was written some time before I became acquainted 

 with Matsumoto's memoir of 1917. I am uncertain whether my O. 

 vexator may not be identical with the Japanese species which he 

 refers to O. verticillatus. 



