OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 139 



The first under arm plate is small, triangular, a little longer than 

 broad, with a convex distal border. The second is quadrangular, 

 broader than long, with a narrow proximal border, very diverging 

 sides strongly excavated by the tentacle pores, and a very broad and 

 convex distal border with the lateral angles very sharp. The follow- 

 ing become pentagonal on account of the resolution of the proximal 

 border into two short sides united by a very obtuse angle. Beyond 

 the second these plates are separated by a narrow interval. 



The side arm plates, which project only slightly, bear seven strong 

 cylindrical spines, rounded at their tip, with a very rugose surface; 

 but the asperities, which are very small and very closely crowded, 

 are only visible under the microscope. Their length increases from 

 the first ventral spine, which is a little longer than the segment, to the 

 last dorsal, which is as long as three segments. 



The tentacle scale is very large and very broad, oval, and almost 

 as long as the segment, with a rounded distal border ; its surface is 

 very rugose. The tentacle pores of the first pair bear two scales, but 

 on those following the scale is always single. 



The color of the specimen in alcohol is entirely white. 



In the specimen from station 5280 the disk reaches only 6 mm. in 

 diameter ; the arms are broken off near the base. It differs from the 

 type specimen which I have just described in having the radial shields 

 relatively smaller, and in the armature of the dorsal surface of the 

 disk, which is composed of more slender and more elongated spines ; 

 furthermore, the interradial incisions are very much deeper. The 

 tentacle scale is very well developed ; it is as long as in the type speci- 

 men, but a little narrower; the proximal angle of the mouth shields 

 is a little less elongated. 



Affinities and distinctive features. — Ophiopttnthaca hastata may be 

 assigned to the genus Ophioplinthaca, although it differs from the 

 other species of this genus by the less deep interradial incisions and in 

 its radial shields, which are smaller and shorter than usual. In this 

 respect it recalls 0. globata, which I have described above, and it 

 stands, like that form, on the dividing line between the genera Ophio- 

 plinthaca and Ophiomitrella; however, it is sharply distinguished 

 from O. globata by the very much larger plates of the disk, by the very 

 small radial shields, by the form of the mouth shields, by the develop- 

 ment of the tentacle scale, etc. 



Ophioplinthaca hastata is rather close to 0. citato, Kcehler, discov- 

 ered by the Siboga, but it is distinguished from it by its very much 

 shorter and somewhat broader radial shields, by the form of the 

 mouth shields, and by the very much larger tentacle scale, which is 

 doubled on the pores of the first pair. It is equally well distinguished 

 from O. vidua Kcehler by the shorter and smaller radial shields, 



