OPHITJRANS OF THE PHILIPPINE AND ADJACENT WATERS. 115 



of the disk does not exceed 3 mm., and a single arm is preserved for 

 only a few segments. 



The disk is rounded or pentagonal, with the interradial regions 

 a little produced. The dorsal surface is covered with plates with 

 very evident outlines, which are rather thick, imbricated, smallest in 

 the central region, becoming larger toward the periphery. Each of 

 these bears a large club spine which abruptly broadens into a well- 

 developed head, and this head is divided into three divergent lobes 

 provided with strong conical spinules (pi. 94, fig. 4). The length of 

 the cylindrical portion of the club spine is almost equal to its diame- 

 ter. These club spines are very closely crowded in the central re- 

 gion of the disk, becoming more separated toward the periphery, 

 their heads at the same time tending to assume a simpler form and 

 to become merely a swelling furnished with pointed spines; then 

 these heads themselves disappear, while simultaneously the club- 

 spine elongates somewhat and from then on resembles a spine. In 

 the large specimen from station 5325, shown in figure 8, the club- 

 spines are more elongated, and their head is less large and is not 

 trilobed, or at least only has very slightly marked lobes ; these club- 

 spines show on their surface very evident spinules, and they thus 

 much resembles true spines, like those which are seen on the border 

 of the disk in the other specimens. The radial shields are small, 

 triangular, and longer than broad ; they may bear toward their distal 

 border two or three club-spines terminated by a few short spinules. 

 The two shields of each pair are slightly divergent, and they are 

 widely separated by two or three series of plates. 



The ventral surface of the disk is covered with large unequal 

 plates, which do not bear club spines except toward the periphery. 

 The genital slits are rather broad. 



The mouth shields are a little broader than long, somewhat lozenge- 

 shaped, with a much elongated and pointed proximal angle, which 

 is produced toward the mouth between the two adoral plates and 

 which is bounded by two very concave sides; the lateral angles are 

 sharp and the distal border is convex and shows in the middle, a 

 more or less prominent rounded lobe; it may be said also that this 

 border is composed of two short sides passing into each other by a 

 very rounded obtuse angle. The adoral plates, which are of medium 

 size, are slightly recurved and crescentic; they are three times as 

 long as broad. The oral plates are small, triangular, and little ele- 

 vated. The lateral mouth papillae, which are four in number, are 

 conical, rather elongated, with the point blunted; the proximal 

 papilla is usually a little broader than the others. The unpaired 

 terminal papilla is thick arid stout and a little more developed than 

 those on either side. 



