136 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



pedicellariae carried on the expanded summit of a retractile sheath which covers 

 all but the tip of spinelet; spinelets and sheaths on disk smaller than those of rays; 

 serial arrangement not very evident except on sides of ray; actinal plates in to 2 

 incomplete series; adambulacral spines two, the inner with a group of pedicellariae, 

 the outer only sporadically; only one pair of postoral adambulacrals in contact; 

 crossed pedicellariae very small, with an unusually broad denticulate terminal lip; 

 Btraight pedicellariae small, ovate, or lanceolate, compressed. 



Dtscr'iption.—linys abactinally well rounded, and disk sometimes slightly 

 higher than base of rays. Spines very delicate, slender, tapered, terete, bluntly 

 pointed, rather widely spaced, each invested by a thick, distally widely expanded, 

 sheath the convex distal surface of which bears very many crowded, small, crossed 

 pedicellariae of characteristic form. These sheaths usually cover all but the tip 

 of the spine, and sometimes extend beyond the tip. In alcoholic specimens the 

 expanded terminal portion is subcircular or irregular in outline as viewed from the 

 end of the spine, 1 to 1.5 mm. broad, and resembles a furry ruff or stole. The spines 

 are all very similar, the abactinal being a little shorter than the marginal and in 

 less evident longiseries. Regular serial arrangement is theoretically present owing 

 to the arrangement of the plates, but some of the carinals, dorsolaterals, and supero- 

 marginals carry two spines, or even three, in the transverse series on the plate. 

 As shown in Plate 18, Figure 5, this breaks up the regularity of the longiseries of 

 spines. The space between the spines varies greatly. Sometimes the stoles nearly 

 touch; sometimes they are widely spaced. In gravid specimens there is usually 

 a broad naked area on either side of the carinal series (which, in such cases, is likely 

 to be fairly regular). The abactinal spines (which are roughened on the distal 

 portion) are 1.5 to 1.8 mm. long. 



The skeleton (pi. 13, fig. 1) is characterized by a partial degeneration of some of 

 the abactinal connectives, by which the carinal plates are more or less (and irregu- 

 larly) isolated. There is a carinal, a dorsolateral, 2 marginal, and to 2 incomplete 

 series of actinal plates as shown in the drawing, where also the position of the isolated 

 rather inconspicuous papulae are indicated. There is evidently started in this 

 species a process similar to that which took place in the ancestors of such diverse 

 genera as Lysasterias, Adelasterias, Pycnopodia, Rathbunaster. Degeneration of the 

 abactinal skeleton is characteristic of very cold water forms, and particularly those 

 of the antarctic. 



The inferomarginal plates carry a single spine with a complete and large ruff 

 of pedicellariae. In some specimens a majority of the superomarginal plates also 

 carry but one spine; proximally, however, there are usually two or three. The 

 actinal spines are rather small and do not occur in any except the largest specimens 

 (R 30 mm.). 



Adambulacral plates regulaily with two slender subequal spines about 1.5 mm. 

 long. Most of the outer spines of the proximal half of ray (and sporadically those 

 of distal half) bear at mid height a thick cluster or pad (sometimes a complete 

 wreath) of very small crossed pedicellariae similar to those of the other spines, 

 while a few of the inner spines carry sporadically a smaller cluster. The first plat? 

 is longer than those following and is in contact with its fellow along two-thirds or 

 three-fourths of the interradial margin, the outer portion of this margin being gen- 



