OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 419 



distinguished, the radials being far removed from the dorsocentral. 

 The plates become a little larger toward the periphery of the disk, 

 and in the middle of each interradial space between the radial shields 

 there is a rather large rounded plate which is somewhat broadened 

 transversely, on either side of which are three or four rows of small 

 plates. Between the two radial shields of each pair there are six 

 to eight more or less regular rows of plates, the median a little the 

 larger. Except in the central region of the disk, where they are 

 entirely unarmed, these plates bear very small spines which are ex- 

 tremely reduced, conical, with the point blunted; each plate may 

 carry from one to three of these spines which are sometimes inserted 

 toward the borders and sometimes over the surface of the plate. 

 These spines are more or less developed in the specimen from station 

 5651 ; in the two others they are not very common and are not seen 

 except toward the periphery of the disk or in the vicinity of the 

 radial shields. These last are rather large, triangular, with the 

 angles very rounded, somewhat divergent, and widely separated by 

 several rows of plates ; they are longer than broad, and their length 

 is equal to a third of the radius of the disk. On their surface in the 

 proximal half and toward the outer border they bear spines identical 

 with those of the other plates of the disk; these spines are a little 

 shorter and relatively thicker in the example from station 5651. 



The ventral surface of the disk is covered with numerous imbri- 

 cated plates, which are larger than those on the dorsal surface and 

 somewhat unequal. Toward the periphery spines identical with 

 those on the dorsal surface are found, but there are only a few of 

 them here. The genital plates are rather large, elongated, and 

 broadened in their distal part. The genital slits are narrow and ex- 

 tend over a length of about two-thirds of the radius of the ventral 

 surface of the disk; they are furnished on their two borders with 

 small and closely crowded papilae. 



The mouth shields are elongated, longer than broad, sagittate in 

 form and pentagonal, with a sharp proximal angle, two straight 

 sides slightly notched toward their distal third by the bottom of the 

 genital slits, and a slightly rounded distal border. In the speci- 

 men from station 5661 these shields are more elongated and nar- 

 rower ; the notching corresponding to the bottom of the genital slit 

 is better indicated, and the distal region beyond is slightly tapering. 

 In the two specimens from station 5650 these shields are thicker 

 and shorter and the lateral notching is very slightly marked. The 

 adoral plates are elongated, triangular, and extremely narrow in- 

 wardly, and they do not come in contact in the median interradial 

 line where the proximal angle of the mouth shield projects; on the 

 other hand, they are markedly broadened outwardly. The oral 



