96 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



with the disk. The diameter of the disk is 9 mm. by 6 mm.; the 

 arms are 25 mm. long. 



The dorsal surface of the disk is entirely covered with rounded 

 granules, which are slightly flattened and very closely crowded, com- 

 pletely covering the underlying plates, which must be quite invisi- 

 ble in the undamaged animal, though in my specimen they may be 

 distinguished in certain regions which have been abraded; they are 

 extremely thin, quite transparent, imbricated, and very finely stri- 

 ated. The radial shields are quite invisible. The granulation is 

 continued with the same characteristics as far as the periphery of 

 the disk, and it passes over onto the ventral surface without show- 

 ing the least modification toward the regions which correspond to 

 the radial shields. These granules have a slightly rugose surface. 

 They are continued on the two or three first upper arm plates. 



The ventral surface of the disk is covered uniformly with closely 

 crowded granules. The genital slits are very broad. 



The mouth shields are large, almost as long as broad, or slightly 

 longer than broad ; they are pentagonal, with a rather open proximal 

 angle bounded by two straight sides, and two slightly excavated lat- 

 eral borders passing over very rounded angles to form the distal side, 

 which is similarly narrow and rounded. On two of the mouth 

 shields I notice that this distal border bears a few granules identical 

 with those on the ventral surface. The adoral plates are elongated 

 and narrow, four or five times as long as broad, and they give off 

 outwardly a rather broad process separating the mouth shield from 

 the first side arm plate. The oral plates are large and elongated. 

 The lateral mouth papillae are about ten in number; they are in- 

 serted on the oral plates and are arranged somewhat irregularly in 

 two rows : there is in addition a group of a few tooth papillae. All 

 these papillae are small, conical, a little longer than broad, and their 

 surface is rugose. In addition to these papillae, I find usually two 

 others, which are inserted on the adoral plate, but which are very 

 elongated and spiniform, and beyond these still another short, oval 

 papilla inserted at the angle between the adoral plate and the first 

 under arm plate. 



The upper arm plates are rather large, triangular, a little longer 

 than broad, and separated by an interval which increases rapidly. 

 I have stated above that the first plates are covered with granules 

 identical with those of the dorsal surface of the disk. 



The first under arm plate, which is of medium size, is broadened 

 transversely ; it is pentagonal, with an obtuse and rounded proximal 

 angle bounded by two straight or slightly excavated sides, two some- 

 what excavated sides, and a short and rounded distal border. The 

 following plates are large, longer than broad, with an obtuse proxi- 



