REPORT ON THE ASTEROIDEA. 507 
8, Hymenaster vicarius, Sladen (Pl. LXXXIV. figs. 3 and 4; Pl. LXXXVI. 
figs. 1-3). 
Hymenaster vicarius, Sladen, 1882, Journ. Linn. Soc. Lond. (Zool.), vol. xvi. p. 223. 
Marginal contour subpentagonal. Interbrachial arcs well indented, the minor radius 
being in the proportion of 69°2 per cent. R=39 mm.; 7=27 mm. The lateral fringe is 
more or less distinct, and its margin forms a line that curves outwards after passing the 
middle of the ray, adding greatly to the appearance of its breadth; the margin then 
suddenly contracts and emphasises the rapid tapering of the ray at the extremity. 
The supradorsal membrane is thin and papyraceous in appearance. The muscular 
fibres are numerous and irregular, rather thick, closely placed, and radiate from the 
tips of each spinelet to those around, thus forming an interlacing web with moderately 
large meshes of rhomboid or quadrate form. ‘The interspaces are filled in with transparent 
membrane, punctured in the centre by a spiraculum; these are moderately large, well 
spaced, and uniformly, though irreeularly, distributed over the abactinal area. The 
paxillaee are numerous, and composed of four, five, or six spinelets, rather short and 
pointed, their tips elevating the membrane into small pointed papille, which are very 
evenly spaced over the abactinal area and appear to rise sharply from the surface, 
whilst their small size and comparative closeness of position give an easily recognisable 
character to the starfish. 
The ambulacral furrows are moderately broad, lanceolate in outline, and taper rather 
rapidly before they reach the extremity, which is in consequence somewhat produced. 
The armature of the adambulacral plates consists of two rather short, cylindrical, and 
pointed spines, covered with an extensive investing membrane which forms an elongate 
sacculus at the tip, and also adds greatly to the apparent robustness of the spinelets. 
The aperture-papillz are large, acumino-spatulate, wide and rotund at the base, and often 
contract rapidly to a point at the free extremity, or may be simply rounded. 
The mouth-plates are small, elongate, narrow, keeled, and prominent aborally. Hach 
bears two short robust secondary surface-spines, one near the adoral extremity, and the 
other placed more aborally near the middle of the plate. The horizontal margins of the 
plate falling into the actinostome are expanded into a rather wide flange, upon the 
edge of which are situated four or five short cylindrical mouth-spines, slightly curved and 
rounded at the tips, but not tapering. 
The actino-lateral spines are delicate, those included within the disk being short and 
not reaching up to the median interradial line, but leaving a rather wide space. The 
longest spine is about the fifteenth from the mouth, but even these do not meet in the 
interbrachial are, where a considerable amount of thickening and deformity of the mem- 
brane occurs. ‘The tips of the spinelets are rather tapering, and not thickened or knobbed. 
The margin of the web is slightly thickened, not indented or festooned. 
