OPHIUKANS OF THE PHILIPPINE AND ADJACENT WATERS. 153 



of plates; their proximal angle is rather sharp; the length of these 

 shields is less than half the radius of the disk. 



The ventral surface of the disk bears only a narrow border of 

 peripheral plates, remaining entirely naked over the rest of its extent. 

 The genital slits are rather broad. 



The mouth shields are lozenge-shaped, as long as broad, with the 

 angles rounded ; the two proximal sides are very gently convex, and 

 the two distal sides are almost straight. The adoral plates are small, 

 triangular, much narrowed inwardly, and scarcely in contact in the 

 median interradial line; sometimes they even do not touch each other; 

 they are much broadened outwardly, and, as they are very close to 

 the median radial line, they include between them the first under arm 

 plate. The oral plates are rather high, half again as high as broad. 

 The internal mouth papilla is large and strong; the following is tri- 

 angular with a very sharp apex ; the external, which is inserted upon 

 the adoral plate, is spiniform and more or less erect ; but it is always 

 short, thick and obtuse. 



The upper arm plates are small, elongated, longer than broad, and 

 almost oval on the two first segments, then broadening somewhat and 

 becoming almost as long as broad with a rather narrow proximal 

 border and a broad and strongly convex distal border continuing the 

 rounded lateral borders. At some distance from the disk the upper 

 arm plates are less confined by the side arm plates, and they then 

 become broader than long, and almost transversely oval. All these 

 plates are in contact. 



The first under arm plate, enclosed by the neighboring adoral 

 plates, is much narrowed in its distal part, but broadens in its proxi- 

 mal part ; it is pentagonal in shape. The following are rectangular, 

 a little broader than long, with the sides straight and the angles 

 rounded ; they are all in contact. 



The side arm plates are much developed, and they encroach con- 

 siderably on the dorsal surface of the arm, especially at the arm bases, 

 where they bear eight spines ; the number of these falls later to seven, 

 then to six. These spines are subequal, and their length equals that 

 of the segment, except that of the last dorsal, which is a little shorter. 

 All these spines are slightly flattened, rather thick, especially the ven- 

 tral spines, and their thickness diminishes from the dorsal side. The 

 first ventral spine is almost cylindrical, with the tip rounded. The 

 two or three following have the extremity obtuse, and often even 

 truncated ; they bear in their distal region very fine asperities which 

 become stronger at their tip; on the posterior angle one of these 

 asperities tends to form a very small tooth, but this feature is only 

 slightly indicated; the four dorsal spines have their tips rounded 

 (pi. 96, fig. 6a). 



