OPHITJRANS OF THE PHILIPPINE AND ADJACENT WATERS. 407 



The ventral surface of the disk is covered with subequal, irregu- 

 larly polygonal or rounded plates, which are slightly imbricated and 

 of medium size. A rather broad and elongated genital plate can be 

 recognized. The genital slits are very narrow, and they appear to 

 extend from the border of the disk as far as the distal angle of the 

 adoral plates. I find on their interradial border some small and ob- 

 tuse papillae which do not always form a continuous row; but the 

 gaps are evidently accidental. 



The rather large mouth shields are pyriform, a little longer than 

 broad, with a sharp proximal angle and a rounded distal border. 

 They are well developed only in three interadii, and in the two others 

 I find instead of these shields and in their place only a small plate 

 resembling those about it. The adoral plates are large and elongated, 

 a little broader outwardly, with the borders slightly sinuous. The 

 oral plates are rather elongated, three times as long as broad. The 

 mouth papillae are six or seven in number on each side; the first 

 proximal papilla is small, but conical and pointed; the two follow- 

 ing are rather low and short, and the distal papillae are thicker and 

 broader, especially the penultimate. The unpaired terminal papilla 

 is elongated and conical, scarcely larger than those on either side. 



The two first upper arm plates are short and transversely broad- 

 ened. The following is quadrangular, as long as broad, with the 

 proximal border narrow, the distal border a little longer, and the 

 sides straight and slightly divergent. The fourth plate is a little 

 longer and narrower, and trapezoidal in form, though it still re- 

 mains a little broader than long. All these plates are in contact, 

 but those following are separated by a wide interval; they are tri- 

 angular with a sharp proximal angle and a convex distal border 

 which may be resolved into two short sides united by a very obtuse 

 angle ; they remain a little broader than long. Their dimensions be- 

 come progressively reduced, though they may be recognized as far 

 as the vicinity of the arm tip. 



The first under arm plate is small, pentagonal, with an obtuse 

 proximal angle, converging and slightly excavated sides, and a 

 straight and narrow distal border. The two following are pen- 

 tagonal, longer than broad, with a straight and narrow proximal 

 border, elongated sides which are more or less excavated by the cor- 

 responding tentacle pores, and two short distal sides united by a 

 rounded angle. The dimensions diminish rapidly from the second 

 to the fourth, which is no longer in contact with the preceding. The 

 following plates become very much smaller and are broadly sep- 

 arated; they are triangular, a little broader than long, with a convex 

 distal border; their size diminishes progressively toward the tip 

 of the arms. 



