420 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



plates are very large and very high, triangular, and twice as long- 

 as broad. The lateral mouth papillae are eight or nine in number on 

 each side; the four or five outermost are rectangular, with the free 

 border straight, and the second is larger than those on either side; 

 the three or four proximal papillae elongate somewhat and become 

 conical with the sides rounded, especially the last, which is stout, 

 rather elongated, and almost of the same size as the unpaired termi- 

 nal papilla. 



The two or three first upper arm plates are transversely broad- 

 ened, short, and quadrangular; the following become triangular, 

 longer than broad, with a very sharp proximal angle and convex 

 distal border; they are at first in contact, then becoming separated 

 by an interval which progressively elongates; they then become as 

 long as broad. These plates bear on their surface a few granules or 

 spines identical with those of the dorsal surface of the disk, the 

 number of which is variable. 



The first under arm plate is small, transversely broadened, 

 lozenge-shaped or simply biconvex in form. The following plates 

 are at first rather large, with the distal border rounded and the sides 

 somewhat convex ; the second is a little longer than broad with the 

 proximal angle rounded ; the third is also a little longer than broad 

 with a sharp proximal angle ; the fourth is as broad as long. These 

 plates are separated by a narrow interval. The following plates are 

 smaller, triangular, transversely broadened with the proximal angle 

 obtuse, and they are very widely separated from each other. All 

 these plates are unarmed. 



The side arm plates, which are not very projecting, bear on their 

 surface, especially in their dorsal region, small elongated granules 

 identical with those on the dorsal surface of the disk and of the 

 upper arm plates, and these little spines may be confused more or 

 less with the true arm spines from which it is difficult to distinguish 

 them. Two principal spines, which are somewhat elongated and 

 situated close to the ventral border of the plate, may be recognized ; 

 there may also be observed near the dorsal border a few granules 

 larger than the others which might be considered as spines. In the 

 individual from station 5651 these spines are best observed (figs. 

 6, 7), but they always are inconstant in their appearance, and it is 

 impossible to say whether they are true spines or not. 



The tentacle pores number three pairs; they are rather large, es- 

 pecially those of the first pair, which carry on each border from one 

 to three scales; the pores of the second pair usually have one ex- 

 ternal or proximal scale and two internal or distal scales; those of 

 the third pair have a single proximal and one distal scale. 



The color of the specimen in alcohol is yellowish. 



