JAPANESE ASTEEOIDEA. 313 



Peiitagonaster Japonicus Sladen. 



(PL XI, figs. 164-170.) 



This species is due to Sladen who described it as follows [ '89, p. 

 272] : 



" Pentagonaster japonicus, n. sp. (PI. XL VI, figs. 1 and 2 ; PI. XLIX. 

 figs. 1 and 2). 



" Rays five. R = 68 mm., r = 50 mm. 11 = 1.36 r. The minor radius is thus 

 in the proportion of about 73 per cent. 



" Body of large size. General form depressed and tliiu. Abactinal area 

 sUghtly convex and capable of being more or less inflated, the inflation 

 being greatest in the radial regions, and emphasised by a conspicuous but 

 shallow sulcus which traverses the interradial lines, but terminates at a short 

 distance from the centre. The interradial channels are of uniform breadth, 

 well defined and smooth, their character and regularity suggesting — fancifully, 

 of com'se — the appearance of a mark produced by the pressm'e of a heated 

 cyhnder. The marginal contour has the forin of an almost regular pentagon, 

 with the sides very shghtly incm*ved, the incm^vatm-e being produced more 

 by a shght prolongation of the ray than by the regular curve of the side 

 as a whole. Margin thick and vertical, equally rounded actinally and 

 abactinally. Actinal area plane or slightly concave, undulating, more or 

 less flexible, and capable of some inflation ; a slight sulcus usually defined 

 along the median inten-adial line. 



" The whole abactinal area is covered with small, regular, polygonal 

 tabula, which diminish in size as they approach the margin (where they are 

 very small) ; they are also smaller in the central region of the disk and along 

 the edge of the interradial sulcus than in the median radial area and on the 

 actual floor of the sulcus. The larger tabula in the radial areas, which are 

 more or less elevated or paxiUiform, are comparatively widely spaced, 

 exposing the papulse, of wliich there are about six round each tabulum, 

 separated from one another by the stellate prolongations of the basal portion 

 of the plates. The paxillfe consist of a hexagonal, rhomlx)id, or polygonal 



