!()(} BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



marginal and actinal papular areas arc frequently confluent, forming very large sub- 

 quadrangular spaces reaching from the superomarginal to the actinal plates. It 

 may happen that a whole scries of inferomarginal plates is thus disconnected. 



On cither side of ray there are three fairly regular series of papulae — an actinal, 

 an intermarginal, and a supramarginal, with one to four in each cluster. The abacti- 

 nal, one to three in each area, are very irregularly distributed and the areas are vari- 

 able in number. Usually the papulae are few. 



Adambulacral plates monacanthid. The spinelets are very slender, terete, 

 blunt, a little shorter and considerably slenderer than the actinals. The spinelet of 

 alternate plates is situated on the furrow margin while the other is spaced back from 

 margin. In the type there is very little difference in size between the two; but in the 

 largest specimen from Unalaska, the outer is longer, heavier, and slightly compressed 

 at the truncate tip. The inner tapers a little, as is usual with furrow spines. First 

 pair of adambulacrals contiguous interradially, conspicuously longer than second 

 pair. 



In the type, 5 of the 10 oral plates carry 2 suboral spines, one carries 3, the 

 rest 1. Other specimens generally carry one. There are two apical spines, both 

 tapered, slender, the inner a little longer than the plate, the outer (adjacent to furrow) 

 nearly as long. Both are longer than in alaskensis. 



Straight pediccllariae (pi. 43, fig. 2), slender to broadly lanceolate, are scattered 

 over lateral abactinal regions; others occur in the intermarginal and actinal channels, 

 in clusters on the oral spines, and sparingly on the furrow spines. Very small ones 

 are scattered along the furrow face of the adambulacral plates. Intermarginal 

 pediccllariae measure about 0.5 mm. long. 



Crossed pedicellariae, very scarce abactinally. A few form rings around the 

 superomarginal spines (sometimes absent), and small clusters on the inferomarginal, 

 actinal, and adambulacral spines. The abactinal and superomarginal (pi. 43, fig. 2a) 

 measure 0.2 to 0.25 mm. long. 



Madreporic body variable in size, medium, situated a little nearer to margin 

 than middle of r. 



Young. — Tho smallest specimen has R 8 mm., and like larger examples has a 

 thick pulpy skin, thrown into folds or welts by irregular deep creases. There are a 

 few carinal spines and one series of superomarginals, one of inferomarginals, and one 

 of adambulacrals, the latter well spaced from the inferomarginals. The spinelets 

 are all slender, and the carinals are nearly obscured by the integument. 



Anatomical notes. — The spinelets are fewer and the plates thinner than is usual 

 in 6-rayed species. The primary spiniferous plates are irregularly roundish or 

 short-lobed and are connected by from 1 to 3 overlapping, flat, spineless ossicles. 

 (PI. 43, fig. 26.) These form the connectives of a very irregular mesh, which abactin- 

 ally may be open, or fairly close. The spaces are larger toward the end of the ray 

 than on the disk and base of arm. The superomarginal plates are larger than the 

 inferomarginal and either three or four lobed. The latter frequently have only the 

 dorsolateral lobes developed. They are then not connected in series, but only with 

 the superomarginals and actinals. When the longitudinal connective is present it 

 is quite slender. 



