62 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



few conical and pointed teeth which are more developed than in the 

 other. The radial shields are almost completely hidden, and only a 

 very small portion of their distal extremity can be seen. 



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

 with club spines identical with those on the dorsal surface, but be- 

 coming smaller and smaller toward the mouth shields. The genital 

 slits are large, elongated, and rather broad. 



The mouth shields, which are of moderate size, are lozenge-shaped, 

 almost as long as broad, with the proximal angle almost a right 

 angle and bordered by two straight sides ; the two distal borders come 

 together over a very rounded angle. The adoral plates are rather 

 elongated, two and a half times as long as broad, tapering slightly 

 inwardly, though in contact in the median interradial line; they 

 broaden a little outwardly and give off a narrow process which sepa- 

 rates the mouth shields from the first side arm plate. The oral plates 

 are triangular and high. The side mouth papillae, three in number, 

 are subequal, conical, and pointed; the outermost is a little broader 

 than the two others. The unpaired terminal papilla is a little larger 

 than those on either side. The upper arm plates are small, triangular, 

 broader than long, and widely separated, with an acute proximal 

 angle and a convex distal border. 



The first under arm plate is rather large, trapezoidal, with a broad 

 proximal border passing over rounded angles into the two sides, 

 which are convergent and which unite over similarly rounded angles 

 to form the distal border, which is short and straight. The second 

 and third plates are triangular, with an obtuse proximal angle and a 

 very convex distal border. Beyond this the plates, which always re- 

 main very large, become pentagonal with an obtuse proximal angle 

 bounded by two straight sides, two straight lateral borders notched 

 by the tentacle scale, and a very convex distal border. They are 

 separated by a narrow interval. 



The side arm plates, which are moderately projecting, carry at the 

 base of the arm seven rather large spines which are cylindrical with 

 the tip rounded and provided with rather feebly developed den- 

 ticulations. Their length increases progressively from the first ven- 

 tral, which is shorter than the segment, to the antepenultimate dorsal, 

 which is almost as long as three segments; the last spine is shorter 

 than that preceding. The dorsal spines of each series come very close 

 together in the dorsal median line of the arms, though without form- 

 ing a continuous transverse series. The under and side arm plates 

 show parallel transverse striations which are very marked, and 

 which are less distinct on the upper arm plates. 



The single tentacle scale is large, lanceolate, rather broad, and 

 pointed, and its length equals about two-thirds that of the corre- 



