OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 409 



meters (70 and 578 fathoms). I have even asked myself whether 

 there were not really of the same species or rather of a variety of 

 the form described by H. L. Clark; but the differences seem to me 

 sufficiently marked to justify a specific separation. 



The disk is rather thick, and its height reaches 4 mm. But this 

 is far from the figure given by H. L. Clark for 0. trychnum, in which 

 the height reaches 6 mm. in a specimen of the disk of which is 18 

 mm. in diameter; the figure 4 mm., representing the height, is meas- 

 ured on a specimen from station 5445 in which the disk has a dia- 

 meter of 22.5 mm. 



The disk is pentagonal, with the sides straight; the two surfaces- 

 are plane and parallel. The arrangement of the dorsal plates re- 

 calls O. trychnum, but the plates which occupy the central region 

 are more numerous; furthermore, the three successive plates which 

 occupy alone each interradial space in O. trychnum are more re- 

 duced, and they are each surrounded by a circlet of very small plates ; 

 these interradial plates, like the radial shields, do not show the least 

 indication of that coarse tuberosity which occurs in O. trychnum^ 

 and which appears to be quite characteristic of that species; in the 

 new species all these plates are simply furnished with rounded gran- 

 ules which are rather closely crowded and only slightly prominent > 

 and do not in any way deserve the name of tuberosities. Beyond the 

 radial shields in place of the three or four plates which occur in O^ 

 trychnum there are to be seen a large number of very small rounded 

 plates forming three more or less regular principal rows, to which 

 are added some other still smaller plates. The two interradial 

 plates which lie at the periphery of the disk are in no way swollen 

 as in 0. trychnum. 



The mouth shields have ,a form slightly different from that shown 

 by H. L. Clark's figures, the sides being parallel and not divergent, 

 and the distal border rounded. 



The form of the upper, under, and side arm plates is the same as. 

 in O. trychnum, but there is an important difference in the number 

 of the arm spines which reaches in the new species eight or nine at 

 the base of the arms, then remaining seven for the greater part of 

 their length, while there are only five or six in O. trychnum. These 

 spines, which are very small, are inserted slightly behind the distal 

 border of the side arm plate, thus forming an oblique row which 

 toward the ventral side progressively retreats from the distal border r 

 the first ventral spines, numbering four on the first segments and 

 three on those following, are very close together and form a small 

 group somewhat distinct from the following spines which are regu- 

 larly disposed at equal intervals. 



To sum up, the principal differences are found in the dorsal 

 plates of the disk, which are simply granulose, and the arm spines. 



