42 ON THE ECHINODERMATA OF THE 



occupied by a number of small paxillse, less than those of the dorsal surface, and seldom, 

 except in largely grown specimens, bearing more than five or six spinelets, and all of a 

 compressed, flat, comb-like form. The paxillse are regularly arranged and closely placed 

 within the area, but only extend for a short distance along the ray, gradually becoming 

 rudimentary as the space between the " ambulacral " transverse combs and the marginal 

 series of paxillae diminishes. 



The mouth-plates are large and somewhat spatuliform, having an armature arranged 

 after the following manner : The two innermost mouth-spines are long, stout, and 

 directed towards the centre of the peristome ; then follow a series of about six or seven 

 spines placed at regular intervals apart, which radiate in the plane of the plate, one after 

 the other, at an increasing angle from the median line. The two most adoral mouth- 

 spines are much longer proportionally than the rest, which gradually diminish in size 

 as they approach the radial series, and being likewise curved somewhat upward from 

 the plane of the mouth-plate, cross and interlock with the corresponding spines of the 

 neighbouring mouth-angle. Between the outer margin of the mouth-plate and the side 

 that falls in the median line of the ray runs a more or less definite keel, upon which is 

 borne a secondary series of seven or eight spinelets, forming a modified comb that stands 

 almost perpendicular to the plane of the mouth-plate, and runs parallel with the 

 marginal series or mouth-spines proper, above described. 



Size. Sars mentions an unusually large example measuring 330 millims. ; but the 

 ordinary size seldom exceeds 200 millims., whilst the northern forms are usually much 

 less; thus at Tromso 80 millims., and at Floro 100 millims. (Sars). 



Colour. Shades of red varying to purple on the upper surface and cream-colour 

 beneath. Occasionally in preserved specimens a trace is left of the natural red colour. 

 According to Verrill, this species is, in the Bay of Fundy, usually deep purple above 

 and orange below ; one large example occurred entirely orange. 



Habitat. On stony or sandy bottoms, from low-water mark down to 90 fms. 

 (Lutkeri). 



Premature Form. In young ten-armed examples from Greenland, 10 millims. in 

 diameter, described by Liitken, the arms are remarkably short (2^ millims.), and the 

 dorsal surface is pretty closely covered with groups of 4-6 spinelets, these immature 

 paxillse being proportionally large and few in number when compared with those on the 

 mature animal. Bordering the margin of the ray there are about eight paxillae that 

 separate the dorsal and ventral surfaces, but do not, as in the case of older stages, lay 

 entirely on the ventral area. Along each side of the furrow is a series of about 14 

 of the transverse " ambulacral " combs, each of four spinelets. The ventral interbrachial 

 areas are still quite small, and have only very few spinelets. Each mouth-plate bears 

 four spines, of which the innermost is longest and is directed horizontally towards the 

 centre of the mouth-opening. The papula? and the spinelets composing the paxilte 

 increase in number with age. 



We have been enabled to confirm the tenour of these observations by a small 

 individual dredged by Captain Feilden, during the outward voyage of the British Arctic 

 Expedition, in lat. 65 N., 26 miles from the coast of Greenland, at a depth of 30 fms., 



