REPOET ON THE ASTEROIDEA. 277 



of the spiniform prolongation of the mouth-plates which is developed in Gnathaster, at 

 even an earlier stage than this. It is to be remarked that Gnathaster is much more hispid 

 in the young stage than in the adult, a character probably common to other forms of the 

 Pentagonasteridse. 



7. Pentagonaster arcuatus, n. sp. (PL LII. figs. 1 and 2 ; PI. XVIII. figs. 5 and 6). 



Pays five. R= 45 mm.; r= 23"5 mm. P = 1"93 r. The minor radius is thus in the 

 proportion of 52"2 per cent. 



General form flat, but moderately thick. Marginal, contour stellato-pentagonal, with 

 the radial angles produced and tapering to an acute extremity, which is slightly turned 

 upward. Interbrachial arcs widely rounded. Margins equally rounded abactinally and 

 actinally. Abactinal area not elevated above the level of the marginal plates ; slight 

 depressions are present in the interradial areas near the margin, which are probably 

 indicative of a limited capability of inflation. Actinal area subplane, with small well- 

 defined depressions external to the mouth-plates. 



The abactinal area is covered with small, subcircular plates, closely placed, united by 

 short, narrow prolongations, which leave interspaces for comparatively large papulaa in the 

 radial regions. The abactinal plates extend to the tip of the ray, two or more series 

 separating the outermost supero-marginal plates from the corresponding plates on the 

 other side of the ray. Seen from above the abactinal plates have a strikingly paxilliform 

 appearance, when their granulation is intact ; the subcircular tabulum is surrounded by a 

 marginal series of small uniform, slightly elongate granules, moderately spaced, and so 

 placed that they appear to radiate slightly apart. Within this ring are several small 

 hemispherical granules, the majority of which are larger than the marginal series, but are 

 in no sense elongate. A small valvate pedicellaria formed by two contingent granules is 

 present on the tabulum of a few of the paxillas, but these organs are of rare occurrence. 

 The plates on the outer part of the ray and those adjacent to the margin throughout are 

 devoid of stellate prolongations, and appear to have more or less of an imbricating 

 character. 



The supero-marginal plates, which are seventeen or eighteen in number, counting from 

 the median interradial line to the extremity, form a well-defined border to the abactinal 

 urea, which diminishes in breadth towards the extremity of the rays. The plates near the 

 interradial line have their breadth rather greater than their length, and the length 

 distinctly increases in a few of the succeeding plates, and then diminishes on the outer 

 half of the ray. The surface of the plate, which is slightly convex in the transverse 

 direction, is covered with rather large, well-spaced, hemispherical granules, those which 

 bound the margin being rather smaller than the others, and regularly disposed in lineal 

 series. The odd terminal plate is very small. 



