OPHIURANS OF THE PHILIPPINE AND ADJACENT WATEES. 135 



Their length is less than half the radius of the disk. In the specimen 

 from station 5656, represented in figure 2 on plate 25, these shields, 

 instead of being elongated, are broadly oval and scarcely half again 

 as long as broad. But in the specimen from station 5123, shown in 

 figure 8, certain shields are much elongated and very narrow, three 

 times as long as broad, while others are shorter and more broadened. 

 Intermediate forms occur in the specimens shown in figures 4 and 7. 



The ventral surface of the disk in the interradial spaces is covered 

 with polygonal plates which are rounded and unequal, and only bear 

 a few rare spherical granules toward the periphery of the disk. The 

 genital slits are broad. 



The mouth shields are small, lozenge-shaped, broader than long, 

 with the four sides almost equal. The proximal angle is obtuse; 

 the distal angle is also obtuse, but much rounded, and sometimes it is 

 prolonged into a small rounded lobe; the two rather acute lateral 

 angles are also slightly rounded. Sometimes the distal angle of these 

 shields is so obtuse and rounded that it disappears altogether, and 

 the mouth shields then become triangular with the distal border more 

 or less convex ; this occurs in the specimen from station 5656 repre- 

 sented in figure 1 and somewhat less marked in that from station 

 5444 (fig. 3). The adoral plates, which are of medium size, are 

 slightly recurved and crescentic, about two and a half times as long 

 as broad, and not broadened outwardly. The oral plates are rather 

 high and triangular. The lateral mouth papillae are usually three 

 in number, and sometimes four : they are conical, strong, and pointed ; 

 there is in addition a very reduced papilla inserted at the angle be- 

 tween the adoral plate and the first under arm plate. Between this 

 last and the third papilla there is a little group of from four to six 

 rounded and closely crowded granules, of which the number and the 

 development varies with the individuals; these granules are also more 

 or less apparent, depending doubtless on the contraction or extension 

 of the neighboring parts. The papilla which is inserted on the first 

 under arm plate is very often confused with these rounded granules. 

 This structure is quite identical with that which H. L. Clark has 

 described and figured in Ophiomitra bythiaspis, and which I also 

 found in Ophioplinthaca pulchra. The unpaired terminal papilla is 

 conical and a little stouter than those on either side. 



The upper arm plates are large and strongly convex, triangular, 

 with a very obtuse and rounded proximal angle, a rounded distal 

 border, and rather sharp lateral angles; these plates are a little 

 broader than long, and they are usually separated from the base of 

 the arms outward by a narrow interval. 



The first under arm plate is small, triangular or pentagonal, with 

 the distal angle bounded by two short sides which are almost as long 



