124 NEW YORK STATE MUSEUM 



In all but the anal interradius there is a single large plate com- 

 pletely surrounded and separated from all other plates by from 

 13 to 14 " supplementary " plates in contact with it. The two upper 

 plates of this circlet are usually the larger and are capped by an 

 additional plate over which meet the first plates of two opposing 

 pinnules. In each right and left posterolateral interradius addi- 

 tional supplementaries increase the total number of plates to 18, 

 the post. IR has two large plates neither of which is completely 

 surrounded by supplementary plates next the r. post. R. 



The third plate of each first pinnule sends inward two thin sheet- 

 like extensions, one each side of the very narrow ambulacral groove, 

 that are five or six times as long as the width of the face of the 

 plate and reach more than halfway in toward the center of the 

 tegmen; the plates above this send in shorter extensions and the 

 fifth plate reaches the edge of the tegmen. The second plates of 

 the second pinnules (the first inner pair of each radius) have 

 similar sheetlike extensions ; the upper edges of the contiguous 

 sheets of these pinnules are covered with a single row of rather 

 large tegmenal plates. 



The tegmen appears to have been supported by a radial series of 

 struts formed in this manner and preventing an inward closing of 

 the bases of the arms ; the tegmen would thus be rigid, not flexible, 

 and would be nearly fiat, the arms closing over it. 



On a level with the upper edge of the first plates of the third 

 pinnules and midway between them and the top of the second plates 

 of the second pinnules there is a rectangular opening into the calyx 

 (10 in all) and a little distance above this is another and larger 

 channel, the food groove, directly roofed over by the small plates of 

 the tegmen, and the ambulacral grooves of the third joint of the 

 second pinnule lead into this opening. The ring of larger plates 

 around the anus is not complete but open toward the center of 

 L. post. R. 



Remarks. I am again indebted to Dr J. F. Whiteaves for his 

 courtesy in allowing me to give some time to the study of this 

 specimen. I wish also to express my obligation to Mr Walter 

 Billings who sent me a cup analysis he had made of the same, show- 

 ing about 140 plates. 



By removing incrustation from the cup, I have been enabled to 

 represent some 90 additional plates but otherwise my analysis does 

 not differ from that of Mr Billings save in the lost calyx plates 

 of L. post. R. (shaded) where I find indications of but two missing 

 plates where Mr Billings gives three. 



