144 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



The supramarginal columns begin at the very apex of the rays 

 and for more than one- third of their length adjoin the mframarginals 

 where ambital plates begin to appear. The supramarginal columns 

 are contmuous over the disk in a broad curve, with about 18 to 20 

 in a column, or from apex to apex of adjoining rays there are from 

 35 to 40 of these plates. In the axillary areas the}^ are separated 

 from the inframargmals by three or four rows of ambital plates. At 

 the apex of the rays the supramarginals are highly convex and 

 nearly circular in outlme but soon pass into more and more dis- 

 tinctly stellate plates. This is the form of all the abactinal plates 

 inside of ^the inframarginals ; they are stellate, highly convex, each 

 with a central node for an articulating spine and a few granules 

 that are the bases for smaller spines. 



Each radial colunm appears immediately beneath the two terminal 

 or rather distal supramargmal plates and then continues as a column 

 to near the center of the disk. They are more prominent than the 

 other columns excepting the marginals and have not less than 25 

 plates in each one. On each side of the radials are five columns of 

 radial accessory plates which appear to contmue as columns over the 

 disk in broad curves joining those of the next ray. Between these 

 columns in the axillary areas are additional accessory plates. These 

 colunuis of accessory plates appear singly, first on one side and later 

 on the other, and not in pairs simultaneously, one on each side of the 

 radial columns. 



Ambital areas well developed in the axillary region, where there 

 are about three columns of these plates. The columns pinch out 

 rapidly distally and none are present in the outer third of the rays. 



The plate arrangement of the central part of the disk can not be 

 made out. 



Madreporite of medium size, highly conical, and conspicuous, 

 with numerous sharp single or bifurcating ridges; on the under side 

 are seen two outwardly directed spiral cones (the white lines of the 

 drawing representing the spiral tubes in the madreporite), reminding 

 one of the brachia in Atrypa (pi. 27, fig. 4). 



Adambulacral plates depressed, convex, subquadrangular in out- 

 line in young specimens, but in fully grown individuals a number of 

 these in the central region of the column are much drawn out laterally 

 and are here two or three times as wide as long. In a half-grown 

 individual there are about 20 of these plates in a column, but in a 

 mature specimen there appear to be not less than 26. These plates 

 end inwardly in an apex, against which terminate the ridges of the 

 ambulacral plates. The adambulacral and inframarginal columns 

 are closely adjoinmg in the distal two-thhds of the rays but proxi- 



