ASTEROIDEA 145 



mistook for adambulacrals. As a variation, there may be a fourth small spinelet in line 

 with the series or else placed aborad to the third spinelet. The whole armature forms a 

 cheval-de-frise along the furrow margin very conspicuously higher and heavier than the 

 small actinal spinelets which are in well-spaced groups of 2, less often 3. The interradial 

 area is crossed by the characteristic deep wrinkles or dermal grooves. 



The inferomarginal groups of 5 or 6 spinelets clearly mark the border of the actinal 

 area and are actinal in position, at the interradius about |r from the ambitus. Above or 

 beyond them the abactinal spinelets are sharply differentiated from the actinals by their 

 heavier investment of skin and the much closer juxtaposition of the paxillae, which 

 carry i, 2, or 3-5 spinelets. These are normally hidden by a sheath common to the 

 whole paxilla. That is, the group of spinelets is enclosed in a wrinkled bag of pulpy 

 tissue (while in fiiscus each spinelet is separately visible). The skin between the crowded 

 sacculate groups is raised into lower deeply wrinkled welts among which it is difficult to 

 differentiate the papulae. These are, however, rather evenly scattered all over the 

 abactinal area, being readily seen from the inner surface of the abactinal wall. The latter 

 is much thicker than in ftisais, but some of the difference must be discounted owing to 

 the greater size of specimen B. This body wall further thickens in the larger specimens. 

 In C it reminds one of the body wall of a leathery holothurian. 



Coming to the details of the spinelets of specimen B (Fig. B, 5^), the resemblance is 

 rather close to aurorae, but the spicules or thornlets build a smaller head to the spinelet, 

 as a rule. Fig. 5 « (left) is a young spine, indicating the terminal origin of thornlets. The 

 spinelets are the same length as in equal-sized specimens of aurorae (o-53-o-63 mm.). 

 The pedicel, however, is a little higher (o-36-o-45 mm.), and distinctly higher than in 

 fuscus. The actinal spinelets are 07-o-75 mm. long and the armature of slender thornlets 

 is no more extensive than in the shorter abactinal spinelets. It is therefore much less 

 than in the actinal spinelets of aurorae. 



In large examples (figs. 5, 5^) the thornlets either are absorbed or are broken in the 

 case of the abactinal spinelets since none could be found having the characteristic 

 structure of fig. 5«. In specimen C the spinelets (fig. 5, enlarged | scale of fig. ^a) are 

 around 0-7-0-75 mm. long and appear to represent only about | of fig. 3. The actinal 

 spines of large specimens (fig. 5^) are also very different. There is no longer any trace of 

 the delicate spicules of specimen C. The terminal third is covered with short asperities, 

 somewhat like rose thorns in shape. Such a transformation is not found in comparable 

 large specimens of aurorae. 



Koehler has fully described the adult with excellent photographic figures. Certain 

 emendations are necessary since he had only the type from Petermann Island. He 

 emphasizes the peculiarity of the large, spatulate, innermost adambulacral spine with its 

 heavy sheath of tissue which forms a membranous expansion along either edge of the 

 spatula, thereby increasing its apparent width. This spatula is not so wide in the 

 Discovery specimens as in the type, and is often not wide at all, but is narrow and gouge- 

 shaped, with a thickened, slightly bifid truncate end, the extremity being one-third to 

 one-half the width of the end of Koehler's figure (pi. 3, fig. 8). This extremely broad 



