OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 185 



do not always reach even to the median interradial line. The oral 

 plates are small, twice as high as broad. The lateral mouth papillae 

 are five in nuirfber, unequal, and a little separated from each other. 

 The two outermost, slightly broadened and elongated, are inserted 

 on the adoral plate, and they cover the opening of the mouth tentacle 

 pore ; the three others are conical, narrow, and pointed, inserted on 

 the oral plate. Besides these there are two or three small tooth 

 papillae which are smaller than the mouth papillae. 



The upper arm plates are very large, and they cover a large part 

 of the dorsal surface of the arms. They are a little broader than 

 long and broadly rounded; in the large specimens their form is al- 

 most circular ; in the smaller they become almost semicircular, with 

 a slightly excavated proximal border (figs. 4, 5) ; in the smallest 

 these plates are triangular, with a more or less distinct proximal 

 angle, and a little longer than broad; their distal border is convex, 

 and sometimes it is resolved into two short sides which pass into each 

 other over an obtuse angle. 



The first under arm plate is rather small, and triangular. The 

 following plates are quadrangular, a little longer than broad, with 

 the proximal border straight, the sides excavated by the tentacle 

 scale, and the distal border a little broader than the proximal border 

 and almost straight ; they are all broadly in contact. 



The side arm plates, which are rather projecting, carry eight or 

 even nine arm spines in the large specimens ; this number falls to six 

 in the small. These spines are very close to each other, slightly flat- 

 tened, subequal, and their length equals almost that of the segment ; 

 their surface is smooth (pi. 96, fig. 7&). 



The single tentacle scale is large, rounded, and oval in form. On 

 the first arm segments there is added to this principal scale a small 

 internal scale inserted on the under arm plate which disappears 

 more or less rapidly according to the size of the animal; this scale 

 in the large specimens is found on at least seven or eight segments, 

 while on the smaller it is only found on the first four or five, and 

 sometimes disappears even more rapidly. The supplementary scale 

 is smaller than the other, cylindrical and slightly spiniform. 



The color of the specimens in alcohol is grayish white or gray. In 

 the two largest the borders of the upper arm plates are margined 

 with a light brownish line, a little more marked in some places than 

 in others, which gives the impression of an irregular and weak 

 annulation. 



Affinities and distinctive features. On account of the number of 

 mouth papillae this ophiuran must be placed in the genus Ampki- 

 iimna. Among the five species known belonging to this genus, three 

 possess two tentacle scales A. caribbaea (Ljungman), A. olivacea 

 (Lyman) and A. pentacantha (H. L. Clark) ; but the two others 



