OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 427 



Their surface is smooth, without the least indication of tuberosities 

 or of any prominences whatever. * 



The ventral surface of the disk is covered with rounded plates 

 which are slightly imbricated and unequal; the larger are a little 

 more developed than the smallest plates of the dorsal surface. The 

 genital slits are narrow. 



The mouth shields are small, elongated, almost twice as long as 

 broad, pentagonal, with a sharp proximal angle bordered by two 

 straight or slightly concave sides passing over into the lateral borders 

 by very rounded angles ; the mouth shields have their maximum width 

 at the level of these angles ; their sides are notched toward the proxi- 

 mal third by the ends of the genital slits, and they pass over by 

 rounded angles to the distal border, which is narrow and slightly 

 convex. The adoral plates are rather narrow inwardly, but they 

 broaden outwardly and form a process which separates the mouth 

 shield from the first side arm plate. The oral plates are very small 

 and triangular. The mouth papillae are usually five in number on 

 each side; the three outer are rather broad; the first is triangular 

 with a pointed apex, the second and the third are quadrangular; 

 the two following papillae are smaller and pointed. The unpaired 

 terminal papilla is not very much larger than those on either side. 



The two or three first upper arm plates are extremely short; the 

 following are quadrangular, with a concave proximal border which 

 is slightly narrower than the convex distal border; their sides are 

 very divergent and straight and they pass over by sharp angles to 

 the distal border; these plates are very much broader than long. 

 As the distance from the base of the arms increases, the proximal 

 border little by little diminishes in length, but it is only near the 

 extremity of the arms that it disappears; the plates then become 

 triangular, and they are almost as long as broad. 



The first under arm plate is small, transversely broadened, pentag- 

 onal, with a very obtuse proximal angle bordered by two concave 

 sides; the two lateral borders are short, and they converge toward 

 the rather narrow distal side, into which they pass over by rounded 

 angles. The following plates are quadrangular, with the proximal 

 border straight and narrower than the convex distal border; the 

 sides are divergent and broadly excavated by the tentacle scales. 

 These plates are at first as long as broad; they then become a little 

 longer than broad, and at the same time their proximal border be- 

 comes more and more narrow, and is finally replaced by a very open 

 angle. All these plates are in contact. 



The side arm plates, which are only slightly projecting, each bear 

 three subequal spines of which the length is almost equal to half 

 that of the segment ; these spines are thick and cylindrical, and their 

 point is rounded ; they are not appressed against the lateral surfaces 



