OPHIUBANS OF THE PHILIPPINE AND ADJACENT WATERS. 177 



papillae are four in number. The terminal papilla is strong, elon- 

 gated, thick, and conical, twice as long as broad ; the three others are 

 rather small and rounded ; the second, inserted on the oral plate, is 

 the smallest, and the third, which arises in the angle between the oral 

 and adoral plates, is larger, somewhat squamiform and broadened; 

 the fourth, which is sometimes separated from the preceding by a 

 narrow interval, is smaller; it is inserted on the adoral plate. Be- 

 tween the first and the second papilla, and on a higher level, may be 

 seen the papilla of the mouth tentacle pore, which is conical and 

 rather short. 



The upper arm plates are very large, and they cover almost the 

 entire dorsal surface of the arms. They are almost biconvex, but 

 the distal border sometimes divides into two short sides which are 

 united by a very obtuse and rounded angle. They are all in contact. 



The first under arm plate is very small, triangular, with a rather 

 marked proximal angle in the specimen from station 5161 (fig. 7), 

 while in that from station 5371 (fig. 9) it is a little larger and rec- 

 tangular. The following plates are pentagonal, with a very obtuse 

 proximal angle, the sides slightly notched by the tentacle pore, and 

 the distal border more or less excavated in the middle; they are a 

 little broader than long in the specimen from station 5371, and in the 

 others they are as long as broad, or even a little longer than broad. 

 They are at first in contact, then becoming separated by a short in- 

 terval at a greater or lesser distance from the disk. 



The rather strongly projecting side arm plates bear at the base of 

 the arms seven or eight spines. This figure falls to six, and then to 

 five. These spines are small, conical, subequal, and a little shorter 

 than the segment. The second and third ventral spines are termi- 

 nated by a small hyaline point recurved toward the arm tip, thus 

 forming a small hook which is more or less accentuated. In the basal 

 half and on its proximal border the second spine ordinarily shows 

 some small fine teeth, which are moderately elongated and closely 

 crowded, but which disappear in the distal half, the latter being 

 merely somewhat rugose, as is also the distal border throughout its 

 whole length (pi. 96, fig. 10b). The other spines are simply rugose 

 (a and c). 



The two tentacle scales are small, oval, and placed at right angles 

 to each other. 



Affinities atid distinctive features. — The incomplete condition of 

 the specimens, which have all lost the dorsal surface of the disk, 

 makes comparisons difficult. The dimensions of the mouth shields 

 separate A. lucidus from all the known species of Amphioplus pos- 

 sessing numerous arm spines and two tentacle scales. There is some 

 analogy with A. laevis Lyman from the Philippines, but this has the 



55269— 22— Bui. 100 12 



