ARCTIC SEA TO THE WEST OF GREENLAND. 25 



The madreporiform body is situated in the interradius, about midway between the 

 centre and the margin of the disk, but generally nearer the centre in fully developed 

 specimens. 



Size. Large examples measure 230 millims. in diameter ; and the species is known 

 to attain even greater dimensions. 



Colour. Dr. Liitken, recording the observations made by Inspector Olrik upon 

 the colour of this Starfish when alive, states that it is generally purple-red, and some- 

 times greyish olive-green. 



Habitat. According to the above-mentioned Danish naturalist, A. polare is to be 

 found at low tides in May and June, but later in the year in deeper water (for instance, 

 in August at 40 fathoms). This species was taken at Arksut by Mr. Barrett, from the 

 shore down to 10 fathoms depth, on rocky bottom. 



Premature Form. A young specimen 28 millims. in diameter (the relative 

 proportions of the disk and radii being 1 : 3'5 approximately) presents the following 

 characters. The rays are broad and stout, tapering near the tip, and have their 

 junction with the disk very frequently marked off by a sharp constriction in examples 

 of this early age. The ossicles of the abactinal network are remarkably stout and 

 robust, the interspaces being small and restricted in consequence ; these are usually 

 round in outline, with the membrane punctured by a single papula only, although two 

 may occur occasionally. The dorsal spinelets are large and truncate, many quite sub- 

 clavate, and are widely spaced over disk and rays alike without any regularity in their 

 arrangement; their bases are closely surrounded by pedicellariae forcipiformes, the 

 large size of which is very striking in this young stage of the starfish, whilst similar 

 pedicellarise also accompany the secondary or intermediate spinelets, which occur with 

 moderate frequency upon the imbricating ossicles. In the small specimen under notice, 

 no pedicellariae forficiformes have been detected upon the abactinal surface either of 

 the disk or rays ; there are, however, a few isolated ones on the margins of the furrows, 

 but comparatively insignificant in size, and scarcely, if at all, larger than the p. forci- 

 piformes of the abactinal surface. 



The madreporiform body, which is large and deeply fissured, lies nearer the margin 

 than in the adult forms, being situated about two thirds of the distance from the centre 

 of the disk to the arm-angle. 



Two longitudinal rows of lateral spines are present, one on the dorsal and the other 

 on the ventral margin, the sides of the ray being vertical. The spinelets of both series 

 are large, stout, cylindrical, and rounded at the tips ; they are isolated and well spaced, 

 the members of the upper series standing immediately over their ventral companions. 

 In dried specimens the dorso-lateral row forms a conspicuous fringe along the margins 

 of the ray, and the bases of the spinelets are surrounded by a wreath of pedicellariae 

 forcipiformes. These are also present at the bases of the ventro-lateral series, though 

 not so numerous, and are there confined principally to the upper side of the spinelet. 

 Between the ventro-lateral row and the ambulacral spines a short series of secondary 

 spinelets extends along the inner half of the ray only ; these are smaller, even at the 

 base of the ray, than the other spinelets, and diminish rapidly in size as they proceed 



