OPHIURANS OF THE PHILIPPINE AND ADJACENT WATEBS. 371 



none of these plates are conspicuous by^ their size. The radial shields 

 are large, triangular, half again as long as broad, and their length is 

 slightly more than a third of the radius of the disk. The two shields 

 of each pair are separated outwardly for a quarter or a fifth of their 

 length by the first upper arm plate which is triangular and trans- 

 versely broadened, and inwardly over a somewhat greater distance 

 by the triangular radial plate mentioned above; these shields are 

 therefore in contact in their middle portion for about a third of 

 their length. The papillae of the radial combs are much elongated, 

 fine, and close together, and below them may be distinguished a 

 small supplementary comb. 



The ventral surface of the disk is covered with plates which are 

 few in number, rounded, subequal, and slightly imbricated. The 

 genital slits are narrow. The genital plates are also narrow and 

 they are provided with papillae which are all very obtuse and short, 

 but which rapidly become elongated at the periphery of the disk. 



The mouth shields are large, longer than broad, pentagonal, with 

 an obtuse proximal angle and a very strongly convex distal border ; 

 the lateral borders are slightly notched by the bottom of the genital 

 slits. The adoral plates are narrow, strongly tapering in their outer 

 quarter, and more broadened inwardly. The oral plates are high 

 and broad. The lateral mouth papillae are five in number; the 

 four outer are small and somewhat irregular; the last is elongated, 

 conical, and almost of the same size as the neighboring unpaired 

 terminal papilla. 



The first upper arm plate is rather large, triangular, broader than 

 long, with a very obtuse and very rounded proximal angle; it sepa- 

 rates the distal portions of the two radial shields of each pair. The 

 second plate, smaller and narrower than the preceding, is rectangu- 

 lar or trapezoidal; it lies between the radial combs. The third is 

 very much larger, trapezoidal in shape, twice as broad as long. The 

 fourth is still broader, though scarcely longer than the preceding. 

 The width of the following plates diminishes beyond the fifth, while 

 their length increases ; these plates then become hexagonal, with the 

 proximal border straight and a little longer than the distal border, 

 which is also straight, and lateral borders each formed by two short 

 straight sides united by an obtuse angle. The length is at first less 

 than the width ; they then become little by little as long as broad, 

 remaining broadly in contact, and finally longer than broad. The 

 two ends, the proximal and the distal, become shorter and shorter 

 so that the plates assume a lozenge-shaped form and toward the 

 extremity of the arms they are twice as long as broad and barely in 

 contact by their adjacent angles. 



The first under arm plate is large, hexagonal, with the proximal 

 border slightly excavated and the distal border somewhat rounded: 



