RETORT ON THE ASTEROEDEA. 225 



character referred to has subsequently been called in question. Sars ' states definitely 

 that it did not occur in any of his specimens, and he considered that Diiben and Koren 

 had been deceived by the presence of foreign matter. Diiben and Koren remark that 

 the character is not a constant one. 



A large series of specimens shows a considerable amount of variation in the relative 

 breadth of the supero-marginal plates and the paxillar area upon the rays. In examples 

 from Drobach the supero-marginal plates as a rule arch over very slightly upon the actinal 

 surface. On the other hand, in a specimen from Tromso in the Christiania Museum they 

 are very wide. This example is also noteworthy on account of the different character of 

 the paxillse, which are more rounded in form, and with the component spinelets radiat- 

 ing more apart ; whereas in the usual type the spinelets are pressed together and directed 

 upward, and the crown is more or less pentagonal in form. The spinelets on the aboral 

 margin of the infero-marginal plates of the Tromso specimen are very insignificant, and 

 are almost aborted into robust squamules. The armature of the adambulacral and actinal 

 intermediate plates, which is papilliform, uniform, and invested with membrane, has a 

 very distinct appearance, as well as the almost naked and flatly appressed covering of the 

 infero-marginal plates. In the Dr0bach specimens the three or four spines on the infero- 

 marginal plates are well developed. 



I have also seen a specimen from Lofoten with broad supero-marginal plates and well- 

 developed spines on the infero-marginal plates, which are rather wide apart and uniform. 



A number of the specimens in the Stockholm collection have the supero-marginal plates 

 arching well upon the abactinal surface, but in an example from Bohusliin the arching is 

 very slight. 



To a certain extent the supero-marginal plates appear to be relatively broader in young 

 forms, and narrower and less arching in the larger examples. 



The most interesting variety I have seen is one in Christiania determined by M. Sars, 

 which bears a ticket inscribed by him, " Varietet med bredere Paxillarfeldt paa Armene og 

 mindre brede dorsale Eandplader. Paa 200 Favnes Dyb paa Line. Fensfjorden." In this 

 example the supero-marginal plates are very narrow and almost perpendicular. The spines 

 on the infero-marginal plates (a series of three to five) are long and thin, the third from the 

 margin being longest. The central part of the plate is naked. Similarly the supero-marginal 

 plates have only a few granules on the upper part and near the margins of the plate. 



Sars : has remarked that the northern examples of this species seem to have generally 

 shorter arms than the southern ones. 



2. Psilaster acuminatus, n. sp. (PI. XL. figs. 1 and 2 ; PI. XLII. figs. 7 and 8). 



Rays five. R = 65 mm. ; r = 15 mm. R = 4*3 r. Breadth of a ray at the base, 

 14"5 mm. 



1 Oversigt af Norges Echinodermer, Cliristiania, 1861, p. 31. 



(ZOOL. CHALL. EXP. — PART LI.— 1888.) 29 



