56 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Under these conditions it has seemed to me that it would not be out of 

 place to apply the name O. longidens to my specimen, which comes 

 from a region very close to that where the Challenger collected the 

 unique representative of the species, and from a similarly small depth, 

 and to give here a detailed description of it. 



The diameter of the disk is 4 mm., and the arms are 18 mm. long. 

 The specimen is not quite complete; three almost entire arms re- 

 main attached to the disk, the other two being detached and broken 

 off at some distance from the base. 



The disk is rounded. The dorsal surface is covered with extremely 

 small and closely crowded plates, each bearing a very slender and 

 very fine club-spine terminating in three remarkably slender spinules 

 of which the length in the central portion of the disk is equal to that 

 of the club-spine itself, but which become shorter toward the pe- 

 riphery. The distal part of the radial shields only is visible, in 

 the form of a small, triangular plate, a little longer than broad, and 

 the two shields of each pair are widely separated ; from each of them 

 there extends a much raised rib which remains distinct for almost 

 half the radius of the disk. 



The plates which cover the ventral surface of the disk in the inter- 

 radial spaces each carry a small and very short club-spine termi- 

 nated by a few spinules, which are also very short. The genital 

 slits are broad. 



The mouth shields are small, very much broader than long, with a 

 rather sharp proximal angle and two slightly excavated sides com- 

 ing together over rounded angles on the distal border, which is 

 convex. This last shows in its center a rounded lobe which pro- 

 jects more or less into the interradial space. The adoral plates, 

 which are of average dimensions, have the long borders parallel and 

 gently recurved in the form of a crescent. The oral plates are very 

 small. The lateral mouth papillae are three in number, elongated 

 and cylindrical, with the point rounded ; the two proximal papillae 

 are rather narrow, and the outermost is a little more thickened ; the 

 unpaired terminal papilla is a little stouter than the others. 



The upper arm plates are small, triangular, a little broader than 

 long, with the distal border convex ; they are widely separated from 

 the base of the arms outward. 



The first under arm plate is small, triangular, with a rounded 

 distal angle. The second is quadrangular with a narrow proximal 

 border, a very broad and strongly convex distal border, and di- 

 vergent sides excavated by the tentacle scale. The following plates 

 become pentagonal as a result of the resolution of the proximal 

 border into two small sides united by an obtuse angle; they are 

 broader than long and are separated by a space which becomes 

 rather large beyond the third plate. 



