REPORT ON THE ASTEROIDEA. 



527 



Cliorological Synopsis of the Species. 



1. Benthaster loyville-thomsoni, Sladen (PI. XCIV. figs. 1-5). 



Benthaster Wyville-TJiomscmi, Sladen, 1882, Journ. Linn. Soc. Lond. (Zool), voL xvi. p. 242. 



Marginal contour substellate. Rays broad at the base and tapering to a very fine 

 extremity. Interbrachial arcs well indented, not rounded ; the minor radius in the pro- 

 portion of 50 per cent. R = 18 mm. ; r = 9 mm. General body-profile much depressed, 

 slightly elevated in the centre of the disk. 



The abactinal aspect is very remarkable, recalling at first sight the appearance of 

 Korethraster. This resemblance, however, is merely illusory, and arises from the presence of 

 prominent tufts of long spinelets that project free beyond the supradorsal membrane. The 

 pedicks of the paxillse are comparatively short, reduced almost to tubercles on the outer 

 part of the rays, bearing about eight to ten spinelets, which are of great length, and expand 

 very slightly apart from one another. The paxillaj stand on cruciform ossicula, the pro- 

 longations of which are very long and thin, and the central portion where they cross little, 

 if at all, widened. 



The supradorsal membrane is represented by a loose irregular spongiform tissue, which 

 fills up the paxillse-crowns near their bases, and extends over the whole abactinal area. This 

 spongy mass is not uniform in thickness or density, and nowhere forms a definite mem- 

 brane. The paxillae-spinelets protrude a great portion of their length through this tissue, 

 and have the appearance of being entangled amongst it, — a conventional definition of their 

 character expressing more than any rigid description of this part of the structure. No 

 muscular fibrous bands, and no spiracula are present. The spinelets, which are trans- 

 parent and vitreous iu appearance, are regularly trilaminate (as may be distinctly seen 

 in every broken section) and taper to a fine sharp point. No trace is apparent of any true 

 membranous envelope to the paxillse. The spinelets on the disk are much longer and 

 more robust than elsewhere, attaining their greatest size in the neighbourhood of the 

 centre. The oscular orifice is rather indistinct, margined by five somewhat irregular 

 tufts or spinelets, longer and more robust than any of the others. No definite or regular 

 valves appear to be formed. It is doubtful to what extent the dermal chamber is 



