260 NEW STARFISHES AND OPHIURANS—rERRILL. vol xvii. 



The upper and lower marginal plates closely correspond in number 

 and elevation. The superior ones are scarcely raised above the level 

 of the disk, so that they are not conspicuous, as seen from above. In 

 the interradial areas they are nearly twice as high as long, but beyond 

 the middle of the arm they become squarish in form ; their surface is 

 but slightly convex; they are separated from each other and from the 

 inferior plates by shallow and narrow grooves, which are bordered by 

 a row of small granules or papillte a little longer than those that cover 

 the rest of the plate, so as to form simple fascioles. In the largest 

 specimens there are about twenty-flv' e superior marginal plates on each 

 side of a ray. The inferior i)lates are nearly the same as the superior 

 ones in size and form and in the furrows or fascioles between them, but 

 the sutures do not always correspond precisely with those of the upper 

 series. The entire outer surface of the marginal plates of botli series 

 is covered with small granules separated by intervals less than their 

 own diameters. 



The interradial areas beneath are rather large, triangular, and occu- 

 pied by groups of closely united, convex, polygonal, and squarish plates, 

 similar in size to the larger ones of the dorsal surface and covered by 

 even groups of granules, much like those of the dorsal surface, but a 

 trifle larger and higher. Tiiese plates form four or five regular rows 

 parallel to the adambulacral j)lates on each side, beside a small tri- 

 angular group next the center of the interradial margin; their regular 

 arrangement and squarish form allows narrow furrows to run from 

 between the adambulacral i^lates to the marginal plates in both direc- 

 tions. Those in the row next the adambulacral plates correspond nearly 

 to the latter in number and breadth ; this row extends to a point about 

 opposite the eighth marginal plate of the ray, the distal plates becom- 

 ing small and irregular and only filling the angles between the adam- 

 bulacral and marginal plates ; but within the limits of the disk the plates 

 of. this row are nearly square, with rounded corners. The granules cov- 

 ering these actinal plates are somewhat elevated, with rounded and 

 somewhat swollen tips, the marginal series on each plate being some- 

 what longer and more divergent than the rest, so as to form rudimentary 

 fascioles between the plates. Tlie number of granules on the larger 

 plates is usually from fifteen to twenty, of which three to six occupy the 

 center of the group, while the others are often arranged so as to form 

 j)retty regular square or rhombic groups, giving a very even and sym- 

 metrical arrangement to the whole area. On some of these plates, near 

 the mouth, one of the central granules is replaced by a small bivalved 

 pedicellaria, similar in size and form to the adjacent granules, but they 

 do not api)ear to be i)resent on all specimens. In some specimens these 

 pedicellarifie become decidedly larger and are furnished with three, 

 four, and even five valves surrounding a central or subcentral pore in 

 a plate; in this case they take the place of the central group of granules 

 and become more numerous and occur on about one-third of all the 



