OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 173 



proximal border broadly convex ; the distal border is slightly rounded. 

 These plates are separated from the base of the arms outward by an 

 extremely narrow space occupied by the side arm plates. 



The first under arm plate is rectangular, a little longer than broad, 

 with the sides slightly excavated. The following plates are large, 

 almost as long as broad, pentagonal, with the proximal angle trun- 

 cated, the sides straight, and the distal border straight or slightly con- 

 cave. They are all in contact. 



The side arm plates carry at first five spines, the number then fall- 

 ing very quickly to four, and a little further on to three. These 

 spines are slender, elongated, conical, and subequal, and their length 

 equals that of the segment. Their surface is rugose, especially that 

 of the second ventral spine, which shows very fine asperities and of 

 which the tip shows two little hooks forming a right angle with the 

 axis of the spine, thus causing it to appear bihamulate; this character 

 is very marked in my specimen. 



The tentacle scales, two in number, are small, elongated and oval, 

 and stand at right angles to each other. 



The color of the specimen in alcohol is slightly pinkish white on 

 the dorsal surface ; the ventral surface of the disk is gray. 



Affinities and distinctive features. — It may be seen from the pre- 

 ceding description that A. conductus is very close to the species which 

 I described above under the name of A. legatus. I have placed them 

 side by side on the same plate so that the resemblances and also the 

 differences might be easily appreciated. The differences do not per- 

 mit of the least confusion between them. The disk, rather flattened 

 with the borders rounded in A. legatus, is thicker in A. conductus, 

 and the plates of the dorsal surface of the disk, which are so closely 

 crowded and so short in A. legatus, are rounded and as long as broad 

 here ; the radial shields are narrower, more elongated, and less diver- 

 gent. The mouth shields are shorter, cordiform, and more broad- 

 ened in A. conductus, while they are relatively elongated in A. legatus, 

 and the adoral plates are always in contact in the interradial median 

 line in A. conductus. The under arm plates are remarkably narrow 

 in A. legatus, and in this respect the difference between the two species 

 is striking. The arm spines, which are six in the first species, have 

 the tip recurved, but, on the other hand, they show fine, elongated, 

 and closely crowded denticulations which are completely lacking in 

 A. conductus where the spines, at first five in number, and then four, 

 are simply rugose, and the second ventral is bihamulate. These 

 differences are sufficient to prevent any confusion between the two 

 species. 



