82 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



preserved, and their length may be estimated as from 55 mm. to 

 60 mm. 



The disk is rounded, excavated in the interradial spaces ; the dor- 

 sal surface is flattened and covered with tine, small, rounded, and 

 imbricated scales of uniform size except in the immediate vicinity 

 of the center where they become much smaller. Each plate bears 

 a slender club-spine, twice as high as broad, terminated by a crown 

 of three or four divergent spinules, which are conical and rather 

 stout. On the surface of the disk are 10 very widely separated 

 radial ribs, only slightly elevated, elongated, and rather narrow, on 

 the surface of which each of the plates bears a club-spine a little 

 stouter than those on the rest of the disk. At the extremity of each 

 rib there may be seen a very small triangular and naked shield. 



The ventral surface of the disk in the interradial spaces is cov- 

 ered with small, rounded, imbricated plates identical with those on 

 the dorsal surface, but bearing club-spines only at the extreme 

 periphery of the disk. The genital slits are very broad. 



The mouth shields, which are rather large, are triangular and 

 slightly broader than long with a sharp proximal angle bounded 

 by two gently concave sides ; the distal border is very strongly con- 

 vex. The adoral plates are rather broad, two and a half times as 

 long as broad, scarcely broader outwardly than inwardly; they 

 send off a very narrow process which separates the mouth shield 

 from the first side arm plate. The oral plates are triangular, twice 

 as high as broad. The lateral mouth papillae are rather numerous 

 and arranged somewhat irregularly; they are at least six or seven 

 in number. The three or four proximal papillae are elongated and 

 conical with the point obtuse, and they are not aligned exactly in 

 the same plane; then follow ordinarily two papillae, sometimes 

 three, which are flattened and very strongly broadened in their outer 

 half in such a way as to appear spatulate. Following these last 

 there are one or two more spiniform and pointed papillae, and often 

 also a spiniform papilla occurs below the last spatulate papilla. A 

 spiniform papilla, smaller than the preceding, is situated at the outer 

 angle of the first under arm plate. At the tip of the jaw there are 

 ordinarily three tooth papillae, one larger unpaired and two a little 

 smaller placed above it; the unpaired papilla may be replaced by 

 two others smaller, in which case there are four tooth papillae. 



The upper arm plates are rather large, a little broader than long, 

 with a rather sharp proximal angle bordered by straight sides and a 

 convex distal edge ; these plates are in contact throughout the greater 

 part of the length of the arms. 



The first under arm plate is of medium size and trapezoidal with 

 a straight and narrow distal border, well developed sides, and a broad 



