532 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



ping paperlike plates irregular in form. Near the end of the costal 

 area they tend to thin out first midway between 2 costae, and at the 

 end of the costal area there is a transverse band of thin, unarmed 

 integument between the costae, interrupted in the specimen from 

 station 5274 in the middorsal region, where the thin plates extend 

 beyond the costal area proper for a distance equal to 1^ disk 

 diameters. 



The plates of these rays, which have a very swollen costal area, 

 are very slightly spaced ; but aside from this the plates of the speci- 

 men from station 5274 are more closely crowded, which is due to their 

 larger size rather than greater numbers. At base of ray there is a 

 row of about 7 closely placed lateral plates. First lateral spine 

 about 1 disk diameter from base; at outer end of costal area they 

 average 4^ consecutive adambulacral plates in length and at about 

 twice the length of costal area from disk 6| or 7 adambulacral plates 

 (16-18 mm.) in length. 



Adambulacral plates of costal area wider than long and, viewed 

 directly from the side, very nearly as high as long. The armature is 

 somewhat variable, but for the proximal part of the ray is usually 



either l^^^ or .. The furrow spinelet at either end of plate 



(about as long as the plate, or the adoral a little shorter) is accom- 

 panied by a second subequal spinelet, obliquely actinad, which com- 

 ports itself more like a furrow than an actinal spinelet. The adoral 

 one, however, is often bent away from the furrow, and the formula 



misht be written • , ., or ^— ^ • Some plates have -. » and in the 



* %+ 1 1+1 1 



type a few • -^.^^ ••-. • The subambulacral spine is, when fully devel- 



oped, 2^ to 3 adambulacral plates in length and rather less than half 

 the length of the corresponding lateral spine. The lateral and adambu- 

 lacral spines are thickly covered with pedicellariae, which are lacking 

 on the side of the large subambulacral spine toward the furrow. 

 The furrow spinelets have relatively large pedicellariae. In the 



specimen from station 5274 the plates have a variable armature -^ — 



or -. and irequently ^ » but not ■^. 



Mouth plates small, each with a long needlelike suboral spine 3^ 

 to 4^ times as long as the plate and very heavily sheathed. On some 

 mouth plates the sheath seems to be common to 2 spines, and is 

 always very thickly covered with pedicellariae. There are 3 marginal 

 spinelets, 1 about as long as the plate at the outer end and another at 

 the inner end, directed across furrow, and 1 slightly shorter on the 



