108 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



in the central region of the disk, covers almost the whole surface of 

 the plate. These granules appear smooth to the naked eye, but under 

 the microscope they are seen to be furnished with very fine small 

 teeth (pi. 94, fig. 2) ; they are continued with the same characters as 

 far as the periphery of the disk and between the radial shields. 

 These last are large, triangular, two and a half times as long as 

 broad, and their length almost equals half the radius of the disk. 

 The two radial shields of each pair are slightly divergent and are 

 separated by a single range of narrow plates ; sometimes they are in 

 contact outwardly, and sometimes they are separated by a small 

 interval occupied by a single plate. 



The ventral surface of the disk is covered with rather small, irreg- 

 ularly polygonal and slightly imbricated plates, on which I only find 

 in very exceptional cases granules similar to those of the dorsal 

 surface. The genital slits are very broad and extend from the 

 mouth shield to the periphery of the disk. 



The mouth shields are small, a little longer than broad, with a 

 rather obtuse proximal angle bounded by two straight sides; the 

 two other sides are slightly excavated, and they pass over two very 

 rounded angles to form the distal border, which is similarly rounded 

 and smaller than the four other almost equal sides. The adoral 

 plates are extremely broad, a little broader without than within, and 

 their length does not very much exceed their width ; their four sides 

 are straight, and they are in contact with each other throughout their 

 entire width in the interradial median line. The oral plates are 

 rather large, triangular, higher than broad. The lateral mouth 

 papillae, three in number, are irregularly arranged ; they are rather 

 broadened, squamiform and rounded; their dimensions diminish 

 slightly from the outermost to the innermost. In addition there is 

 a group of three or four tooth papillae which are more elongated 

 and conical, with the point blunted. 



The arms themselves are not very large, and their width scarcely 

 exceeds 3 mm. even at the base, but the arm spines, which are very 

 long and stout, help to give them a general appearance of extensive 

 development, the more so since the arm segments are rather short. 

 The upper arm plates are small, triangular, twice as broad as long, 

 ,vith an acute proximal angle bounded by two straight sides, a 

 slightly convex distal border, and sharp lateral angles; they are 

 separated from the base of the arm outward by a space almost equal 

 to half their length which is occupied by the side arm plates. 



The first under arm plate is rather large, triangular, broader than 

 long, with a broadened proximal border and a rather open and 

 rounded distal angle. The following plates, which are of medium 

 size, are rectangular, broader than long, with a straight and rather 



