118 BULLETIN 100, UNITED STATES NATIONAL. MUSEUM. 



speak further on, by the characters of the dorsal plates of the disk 

 and by the very small upper arm plates which are separated from the 

 base of the arms outward. 



This genus is represented in the Albatross collections by two spe- 

 cies, but unfortunately each includes only a single specimen of rather 

 small size; in one of the two the plates of the dorsal surface of the 

 disk bear extremely developed spines, which are as thick as the arm 

 spines ; in the other, which I take as the type of the genus, the spines 

 are very much fewer and shorter and are reduced to simple granules. 



Type of the genus. — OpMoripa marginata, new species. 



OPHIORIPA MARGINATA, new species. 



Plate 23, figs. 1, 2. 



Locality. — Albatross station 4781. One specimen (Cat. No. 

 41129, U.S.KM.) 



Description. — The diameter of the disk is 4 mm. ; the arms are in- 

 complete, but they appear to be very short and could scarcely have 

 exceeded 10 mm. in length. 



The disk is rounded. The rather swollen dorsal surface is covered 

 with large subequal plates which are rounded and thin and show a 

 very clearly marked narrow transparent border; their surface is 

 finely granulose, but the granules do not pass onto the peripheral 

 border. The plates of the central region are larger than the others, 

 though a distinct primary rosette can not be recognized. The plates 

 become smaller in the interradial spaces toward the periphery of the 

 disk; in the vicinity of the edge of the disk or on the edge itself 

 some of the plates bear a large elongated and rugose granule. I do 

 not believe that these granules were more numerous on the living 

 animal or that they occurred over the whole extent of the dorsal sur- 

 face of the disk ; in any case I do not see the least indication of scars 

 left by granules which have been rubbed off. The radial shields are 

 a little larger than the large central plates ; they are triangular, with 

 the angles and the sides rounded, almost as long as broad, and the 

 two shields of each pair are in contact for almost their entire length, 

 which scarcely reaches a quarter of the radius of the disk. 



In the interradial spaces the ventral surface bears a small number 

 of plates similar to those on the dorsal surface and showing, like 

 them, a thin marginal border, but narrower and less evident. These 

 plates occupy almost the distal half of the space included between 

 the edge of the disk and the mouth shields; in the other half the 

 plates suddenly become extremely small, very closely crowded, and 

 imbricated. The very broad genital slits extend from the mouth 

 shield to near the edge of the disk. 



The mouth shields are rather small, triangular or lozenge-shaped, 

 much broader than long, with a very obtuse proximal angle bordered 



