OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 43 



is continued over the dorsal surface in the form of a deep and nar- 

 row depression which reaches almost to the center. The dorsal sur- 

 face is covered by rather large, somewhat unequal, imbricated plates 

 smallest in the central region and becoming larger in the neighbor- 

 hood of the radial shields as well as in the interradial spacer A 

 row of two or three large plates separates the two radial shields of 

 each pair throughout their entire length. These shields, which are 

 of moderate dimensions, are triangular, half again as long as broad, 

 with the external border convex and the proximal angle rounded; 

 their length is equal to almost two and a half times the radius of 

 the disk. 



The ventral surface of the disk is covered with small subequal 

 imbricated plates. The genital slits are rather broad. 



The radial rather small shields are triangular, as broad as long, 

 with a sharp proximal angle bounded by two straight sides and a 

 strongly convex distal border showing in the middle a small, more 

 or less developed, rounded lobe which may give to some of these 

 shields an almost lozenge-shaped form. The adoral plates are short 

 and rather broad, broader without than within. The oral plates 

 are triangular, but elongated, more than twice as high as broad. 

 The lateral mouth papillae, five in number, are A^ery unequal; the 

 three outermost papillae are broadened and scale-like, especially the 

 two last; the two internal papillae, on the other hand, are small, 

 narrow and pointed; the unpaired terminal papillae is rather large 

 and strong. 



The upper arm plates are large and much broadened, triangular, 

 twice as broad as long, with a very obtuse and rounded proximal 

 angle bordered by gently rounded sides, and an almost straight 

 distal border. At some distance from the base the proximal angle 

 becomes truncated, and the plates become quadrangular, with a 

 short proximal border. In the terminal portion of the arms the 

 proximal angle reappears and even becomes very acute, while at 

 the same time the plates elongate so that they end by being a little 

 longer than broad. These plates are in contact, except near the 

 arm tips. 



The first under arm plate is small, a little longer than broad, 

 pentagonal, with a very obtuse proximal angle and parallel sides 

 passing over rounded angles into the distal border which is narrow 

 and gently convex. The following plates are very large, extremely 

 broad, twice as broad as long ; they are quadrangular with an almost 

 straight proximal border, and a very broad and convex distal 

 border showing in the center a more or less marked notch and pass- 

 ing over by sharp angles into the sides which are divergent and 

 strongly excavated by the corresponding tentacular pores. In the 

 terminal portion of the arms the plates become pentagonal with an 



