REPORT ON THE ASTEROIDEA. 185 



united by broad ligamentous bands. Their armature consists of about seven spines 

 arranged in pairs one behind the other, forming a biserial group transverse to the furrow. 

 The innermost spine advances prominently into the furrow, its base being conformable 

 with the angular projection of the plate, and those of the inner pair or triplet, as the case 

 may be, are slightly longest, the others diminishing as they recede from the furrow. 

 Sometimes on the outer edge of the adambulacral plate there may be a lineal series parallel 

 to the furrow of two or three small papilliform spinelets in addition to the spinelets 

 above noticed, but it is always difficult to distinguish these from the armature of the 

 small intermediate plates, which intervene between the marginal and adambulacral 

 plates along a great part of the ray. It may be remarked that the armature of the 

 adambulacral plates simulates in a most striking manner the character of that occurring 

 in Cribrella. 



The mouth-plates, which are small and comparatively inconspicuous, form sharply 

 pointed mouth-angles. They bear on their free margin a series of spines similar to, and 

 at the inner end as long as, those on the adambulacral plates, and along the actinal surface 

 of the plate a lineal series of smaller spinelets running parallel to the median suture, all 

 diminishing in length as they recede from the mouth. 



The actinal interradial areas, though rather small, are well defined on the actinal area 

 of the disk, and extend as a narrow strip far along each ray ; in large examples they may 

 be traced fully along the inner half of the ray and sometimes further. On the actinal area 

 of the disk a row of three or four intermediate plates may be counted between the mouth- 

 plates and the marginal plates on each side of the median interradial line, but these outer 

 series of plates soon disappear. All the plates on the disk-area bear groups of small 

 spinelets, simulating paxillee, the spinelets being delicate, subclavate, and rather smaller 

 than those on the abactinal paxillse proper. Along the ray, however, the spinelets on 

 the intermediate plates are almost indistinguishable from the spinelets on the adambulacral 

 plates. In some specimens the spinelets are much more grouped than in others, and when 

 this is the case the plates as indicated by the spinelets appear more distinct and clearly 

 defined. 



I have been unable to satisfy myself positively whether this species is proctuchous or 

 not. I have, however, certainly detected the presence of a minute pore in some examples 

 of Leptopty chaster arcticus, var. dongata, but whether its functions are those of a true 

 anus, I am not at present in a position to say. There is no modification of the paxilke 

 in the central region of the abactinal surface. 



The madreporiform body is hidden from superficial view by paxillse. In small 

 examples indications of its presence may be detected at about one and a half or two of 

 its own diameters distant from the marginal plates. 



The ambulacral tube-feet have a rounded and well-defined terminal knob. 



No pedicellarise of any kind are present. 



(ZOOL. CHALL. EXP. — PART LI. — 1888.) 24 



