230 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



The superomarginals, 44 to the ray in the type, are all broader 

 than long, as in ctenipes^ the fourth or fifth being the widest, beyond 

 which they very gradually decrease in breadth, being separated by 

 but a single series of flat granulose plates, wider than long for about 

 half the ray, and square or slightly longer than wide on the outer 

 half. There are 56 to 63 of these plates in the 2 largest s];^cimens, 

 and they vary from a trifle less to a shade more than half as wide 

 as the adjacent superomarginal. The granules are spaced more than 

 their width and are similar to those of the superomarginais. The 

 superomarginal granules are rather deciduous, truncate, roundish, 

 and spaced one-half to decidedly more than their own diameter, 

 especially distally. One can count 8 to 10 granules in the length of 

 a plate, not including the very regular peripheral series bounding 

 the narrow well-marked groove between the plates. Terminal plate 

 obovate, granular. 



The inferomarginals correspond to the superomarginais and on 

 the rays are narrower. Beyond the third or fourth plates they are 

 in contact Avith the adambulacrals, and 13 of the latter correspond 

 to 10 inferomarginals at the middle of the ray. The plates are cov- 

 ered with small granules, rather widely spaced on the inner third of 

 the plate; and judging by Sladen's figure (pi. 53, fig. 2), much 

 smaller, more spaced, and less squamiform than in ctenipes. The 

 granules are shorter in proportion to the width and in form are 

 somewhat thimble shaped, the ends being sometimes swollen. The 

 plates have 6 to 10 slender, sliarp spinules arranged in a zigzag series 

 or 2 irregular series the whole width of the plate and decreasing 

 slightly in length from the inner to outer sides of the plate. They 

 are two-thirds to about the length of the outer end of the first plates 

 and decrease in number distad, there b-iing 3 or 4 at the middle 

 of ray, then 2, a single spinule persisting to near the end of the 

 ray. As they are very deciduous, their ]3resence on the outer part 

 of the ray can be detected usually only by the scar. These spinules 

 are more numerous and conspicuous and are distributed much farther 

 along the ray than in ctenipes. 



Actinal interradial areas increasing in size with age ; in the largest 

 specimens the plates extend aborally 3.5 to 4.5 inferomarginals, and 

 there are 5 chevrons, without an odd interradial plate at the apex. 

 Plates covered with uniform spaced, small, clavate, papilliform 

 spinelets bent toward the margin. Nearly all the plates of the 2 

 chevrons nearest the furrow, and a variable number in the other 3 

 also (sometimes nearly all, sometimes 2 or 3 only) bear a slender, 

 sharp, appressed spinule directed toward the margin. These are 

 usually absent in specimens in which R is less than 50 mm. The 

 spinules are absent in P. ctenipes. but the type is smaller than any 

 specimen of hy 2) acanthus, M'hich has them well developed. 



