OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 397 



and widely separated; they disappear after the twelfth segment. 

 Their form is triangular. The first plate is a little more developed 

 than those following and is longer than broad ; the others are very 

 small, as long as broad, or even a little broader than long. 



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

 proximal angle, slightly convergent sides, and a narrow distal border. 

 The two following are large, pentagonal, a little longer than broad, 

 with the distal border almost straight; they are widely separated. 

 Beyond this the ventral plates are entirely lacking. 



The side arm plates carry seven spines at the base of the arms, 

 and beyond only six. In the largest specimen from station 5423 the 

 spines number eight at the base. These equal spines form a regular 

 series toward the distal border of the plate; they are slightly coni- 

 cal and rather elongated, with the point rounded. 



The tentacle pores number two pairs only; they are rather large 

 and covered each with a single oval scale larger on the pores of the 

 first pair than on those of the second. 



The color of the specimens in alcohol is yellowish. 



In figure 1 I show the specimen from station 5263, which is larger 

 than the others and more robust ; the diameter of the disk is 24 mm., 

 and the arms are almost 5 mm. in width at the base. The radial 

 shields, always very large, have the proximal angle strongly 

 rounded, which slightly diminishes their length; among the dorsal 

 plates of the disk some may be distinguished which are a little 

 larger than the others, and six of these without doubt represent a 

 primary rosette in which the five radials are widely separated from 

 the dorso-central. There may be as many as nine spines at the base 

 of the arms, but this number falls quickly to eight and then to seven. 



The specimen from station 5114 is smaller than that from station 

 5127; the diameter of its disk is 14.5 mm. I give a photograph of its 

 dorsal surface in figure 4. This specimen shows a facies somewhat 

 different from that of the others, resulting from having the plates 

 of the dorsal surface of the disk all slightly swollen; the side arm 

 plates are also a little more swollen than usual. The plates of the 

 central region of the disk are not as numerous as in the other larger 

 specimens; this is also the case in the small specimen from station 

 5423, but while in this last the primary radial plates are rounded, 

 here they are broadly oval and almost twice as long as broad. Fur- 

 thermore, all the characters of the species are well marked, and there 

 can be no question of applying another name to this individual. 



Affinities and distinctive features. — OpMomusium facetum must be 

 placed among the species of OpMormismrn in which the under arm 

 plates are not continued beyond the disk and which possess only two 

 pairs of tentacle pores. It may be compared with O. validum Lyman. 



