OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 103 



well as a new species which I shall describe below, may find a place. 

 This genus will have the following characters : 



Ophiacanthidae near the genus Ophiomitrella, from which they 

 differ in the small number of plates covering the dorsal surface of the 

 disk; these plates are in compensation rather large, and they are 

 sometimes enough developed to attain a size nearly equal to that of 

 the radial shields; these latter are also rather large, and the two 

 shields of each pair are in contact throughout their entire length; 

 besides these plates there occurs on the periphery of the disk a very 

 well-developed plate occupying the whole interradial space, or at 

 least the greater part of this space, between the pairs of radial 

 shields; this plate passes over to the ventral surface of the disk, 

 which it in a very large part covers, the remainder of this surface 

 being occupied by a very small number of plates. The outermost 

 mouth papilla is more developed than the others, and is ordinarily 

 much broadened ; the others, few in number, form a regular series to 

 which is added a terminal unpaired papilla. The adoral plates, which 

 are very broad and rather short, do not separate the mouth shield 

 from the first side arm plate. The arms are more or less moniliform, 

 slender, and elongated ; the under arm plates occupy the whole width 

 of their ventral surface, and they are separated very widely by the 

 side arm plates, as are also the upper arm plates. The arm spines are 

 much elongated on the first segments, and the two lateral rows come 

 very close together in the dorsal median line. There is a single 

 tentacle scale. 



I can not say anything in regard to the internal structure, having 

 had at my disposal only a single specimen of O. stultus, and a single 

 adult of the new species, which I assign to the same genus. 



Some years before the publication of Matsumoto's final memoir, 

 which appeared in 1917, I had applied a name to this genus, which 

 I considered as new ; since I have studied this memoir I have become 

 aware that the genus Ophiurothamnus, created by Matsumoto, exactly 

 corresponds to my new genus. I hasten, therefore, since I am still 

 able to do it, to replace the name which I had chosen by Ophiuro- 

 thamnus, which the Japanese naturalist proposes. If the characters 

 which I assign to my genus, and which I have not modified, are 

 compared with those which Matsumoto has given for the genus 

 Ophiurothmnnus, it will be seen that they are perfectly in accord, 

 excepting only concerning the transformation of the ventral spine 

 into a hook in the distal portion of the arms, which Matsumoto indi- 

 cates as being characteristic of the new genus; but this occurs only 

 in one of the four species assigned by Matsumoto to the genus 

 Ophiurothamnus — Ophiothamnus laevis Liitken and Mortensen. I 

 may state in the most explicit way that the first ventral spine retains 



