316 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



membrauf ; paxillae not so widely spaced as in borealis, nearly as in dawsoni; on the 

 rays and peripheral portion of disk about their owti diameter apart, more crowded 

 on center of disk; niar<;iiial plates in two series, the superomarginals about the size of 

 larger paxilla*, and standing above and between the prominent fan-shaped infero- 

 marginal paxillae; latter with constricted base and semicircular summit bearing 

 numerous spines decreasmg in size toward upper end; adambulacral furrow spine- 

 lets long, four or tliree, then three, two, and finally one at end of ray; actinal series 

 curved aborad at inner end and with proximally five to eight, distally three to five 

 longer slender spinelets; mouth plates with eight to eleven marginal and about 

 fifteen suboral spines. 



Description. — Abactinal paxillffi very numerous, low, tabulate (similar to those 

 of dawsoni), with a roundish crown of numerous very short denticulate spinelets 

 immersed in membrane. On the disk the paxillse are not very uniform in size, and 

 larger toward center, where they are spaced less than their own width. On the 

 periplieral half of the disk and on rays the paxilh^ are not so close together, but are 

 spaced about their ow^l width apart or shghtly more. Here they are arranged in 

 very obliciue transverse rows, and also in fairly even cross rows, but a longi- 

 tudinal arrangement is not so evident (so-called cjuincunx order). The larger 

 paxillaj of disk have thirty to forty thick, fleshy spinelets forming a slightly convex 

 crowai, the pei-ipheral series of ten to fifteen being the largest, the rest decreasing in 

 size toward center. On the proximal part of the ray the paxillie have about the 

 same number of spinelets, but the whole paxilla is smaller, and they decrease regu- 

 larly in size toward tip of ray and to a less extent toward the margin. The spine- 

 lets are less heavily enveloped on the ray. The spinelets themselves are slender, 

 even cm the disk, wdth numerous denticles at the tip. An undried paxilla is about 

 as high as the wadth of the crown of spinelets; when tkied, slightly higher. 



Abactinal plates along lateral area of ray regularly four-lobed, each plate 

 imbricating with four others by the length of a lobe, the regular meshes thus formed 

 containing one, two, or near median area, three papulse. Along midradial line and 

 center of disk (out about to madreporic plate) the plates are very irregular, having 

 three, four, or five lobes, and the primary plates on disk are ii-regularly connected 

 by oblong or irregular ossicles forming very irregular and unequal meshes which 

 contain two to five papulae. Along midratlial region there are two or three to a 

 mesh. 



Marginal plates in two series, and of very unequal size, the superomarginals 

 alternating with uiferomarginals. Superomarginals considerably larger than 

 adjacent abactinal paxillae, and about as large as largest paxillae qf corresponding 

 midradial region. Each plate stands opposite the interval between two infero- 

 marginals, and on a level wdth the upper edge of the latter (not crowded between). 

 Inferomarginals (about sixty to a ray) large, paxilliform, with a much compressed 

 fan-shaped pedicel with a curved outer border or summit bearing thirty to forty 

 spinelets, which decrease very rapidly in length from the lower ones, which are in 

 two series and about as long as half the width of summit of pedicel, to the upper 

 which are in three or four series and the same size as spinelets of abactinal and 

 superomarginal paxilhv. Inferomarginals spaced about their own height apart 



