92 BULLETIN" 100, UNITED STATES NATIONAL MUSEUM. 



less damaged, I believe that it is advisable to give here a description 

 of those from station 5450, which are in an excellent state of preser- 

 vation, and then to compare these with the others. . 



The disk is pentagonal, slightly excavated in the interradial spaces, 

 and also somewhat deformed. The flat dorsal surface is covered by a 

 very thin integument on which may be made out under the micro- 

 scope small, extremely thin, and imbricated scales; these scales are 

 very difficult to distinguish in the central region of the disk, but they 

 become more apparent toward the periphery and in the vicinity of 

 the radial shields. These latter are very evident, and through their 

 white coloration they stand out in strong contrast against the dark 

 green color of the rest of the disk ; they are much elongated, biscuit- 

 shaped, four times as long as broad, with the extremities strongly 

 rounded. For more than half their surface these shields are covered 

 by the general integument of the dorsal surface which only leaves 

 exposed a part of their distal region in the form of an elongated 

 triangular area. The two shields of each pair are widely separated 

 by a space at least equal to twice their width. 



The ventral surface of the disk in the interradial spaces is covered 

 by an integument which is somewhat thicker than that of the dorsal 

 surface, and the scales which overlie it are thicker, more evident, and 

 somewhat larger. The genital slits are extremely broad; the genital 

 plates are narrow and elongated. 



The mouth shields are rather large, triangular, with the angles 

 rounded; their distal border carries in the middle a small similarly 

 rounded lobe. These shields are broader than long in one of the two 

 specimens from station 5450, and in the other they are almost as 

 broad as long, forming an equilateral triangle, with the angles less 

 rounded than in the first. The adoral plates are large, very tapering 

 inwardly, but in contact in the interradial median line, much broad- 

 ened outwardly, and widely separating the mouth shield from the 

 first side arm plate. The oral plates are high and narrow, three times 

 as high as broad. The lateral mouth papillae, which are only slightly 

 developed, are small, conical, and short, numbering five or six on each 

 side, and forming a more or less regular row ; there are in addition 

 one or two tooth papillae; toward the other extremity of the jaws 

 there can be made out two and sometimes three small papillae, which 

 are very low and conical, situated on the interradial border of the 

 mouth tentacle pore. 



The first upper arm plates, which continue the small plates of the 

 dorsal surface of the disk separating the two radial shields of each 

 pair, are small, irregular, and arranged in several rows on the two 

 first arm segments, but beyond the plates become larger and are ar- 

 ranged very regularly. They are quadrangular, lozenge shaped, 



