OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 83 



and convex proximal border. The second is very large and very 

 broad, very much broader than long, with a straight and narrow 

 proximal border, very strongly divergent sides which are excavated 

 by the tentacle scale, and a convex distal border. The following are 

 pentagonal, with a very obtuse proximal angle and the distal border 

 always strongly convex; their length progressively diminishes be- 

 yond the third, and they end by being as long as broad, and finally 

 longer than broad. Beyond the second these plates are separated by 

 a narrow interval which becomes progressively elongated as the plates 

 become smaller. 



The side arm plates, which are strongly projecting, bear eight 

 spines, of which the length increases from the first ventral, exceeding 

 the segment, to the last dorsal, which is at least as long as four seg- 

 ments. On the first arm segment the two lateral columns come very 

 close together in the dorsal median line. These spines are rather 

 slender, vitreous, furnished with rather evident and well-spaced 

 denticulations ; these denticulations are especially developed on the 

 ventral spines, and they may completely disappear on the large dorsal 

 spines. 



The under and side arm plates in the proximal portion of the arms 

 show on their surface rather prominent concentric striations; these 

 striations are scarcely indicated on the upper arm plates. 



The single tentacle scale is rather large, somewhat broadened, and 

 pointed ; it shows on its borders small asperities which are especially 

 developed toward its tip; its length equals almost that of the cor- 

 responding under arm plate. The pores of the first pair are provided 

 with two smaller and rounded scales. 



In the specimen in alcohol the dorsal surface of the disk and of the 

 arms is light brown ; the spines and the ventral surface of the disk 

 are white. 



Affinities and distinctive features. — On account of the arrangement of 

 the mouth papillae it seems to me necessary to place this species in Ver- 

 rill's genus Ophiotreta; its two external mouth papillae are broadened, 

 and these papillae are greatly developed, showing a spatulate form 

 which is doubtless characteristic of the species. The presence of two 

 tentacle scales on the pores of the first pair is likewise rather often 

 observed in the genus O phiotreia. But 0. spatvlifera is easily dis- 

 tinguished from the other species of this group by having the dorsal 

 surface of the disk armed with very slender elongated and narrow 

 club-spines ending in a crown of fine spinules, as well as by the spatu- 

 late form of the two outer mouth papillae. 



