JAPAXESE ASTEROIDEA. 183 



a line parallel to the furrow, also fattened and more squarely 

 truncated at the top, slightly shorter than the first three. Then 

 follows a tliird irregular group of half a dozen to about fifteen 

 spines of different sizes and shapes, the inner ones being like the 

 foregoing spines, while the outer ones are more like the inner 

 marginal spinelets of the inferomarginals. When there are only 

 two spines in the second group, they form a horse- shoe shape 

 ■with the spines of the first group, and enclose a central space, on 

 the outside of which the remaining spines form a closely set group. 

 Mouth -plates. — The mouth-plates, though not particularly larger 

 than in Astrop. scoparnis and Astrop. polyacanthus in denuded 

 specimens, bear a larger number of spines, and are consequently 

 more conspicuous. As usual, there is a main ridge running through 

 the whole length of the plate, and a secondary ridge which is 

 nearly half as long. The secondary ridge runs along the am- 

 bulacral furrow and bears about five fiattened spines, of which the 

 innermost is conspicuously larger (PI. IV, fig. 73). On the main 

 ridge, there are at least two rows of spines, in the inner of which 

 the spines are stout and more or less flattened, and in larger 

 specimens tend to crowd out one another, in consequence of which 

 they assume a more or less irregular arrangement. The spines 

 at the central end of this row is very thick and longer than the 

 others, and together with the innermost spine of the secondary 

 ridge, constitute the oral armature. There may be as many as 

 fifteen or sixteen spines in this row, of which a few at the 

 peripheral end are conspicuously larger in smaller specimens. 

 The spines of the outer row are smaller than those of the inner 

 and are 8-15 in number, according to the size of the specimen. 

 The third row, when present, consists only of about a dozen very 



