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REPORT ON THE ASTEROIDEA. 
Chorological Synopsis of the Species. 
Ocean, Range in Fathoms, | Nature of the Sea-bottom. 
Benthaster penicillatus 0 4 Pacific. 1070 Blue mud. 
Benthaster wyville-thomsoni . A Pacific, 2900 Red clay. 
1. Benthaster wyville-thomsonz, Sladen (Pl. XCIV. figs. 1-5). 
Benthaster Wyville-Thomsoni, 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 percent. R=18mm.; r= 9mm. 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 
pedicles of the paxillae 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 paxillz 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 paxillee-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 paxillze-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 in 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 paxille. 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 
