80 PROF. V. J. BELL ON THE [Feb. 19, 



racters. He speaks, for example, of the difference of the form of the 

 body between N. armata and any species of the genus Oreaster, as 

 he regards it. But a comparatively insignificant difference in the 



n 



value of — is not even a subgeneric character. The second point of 



difference is, in Prof. Perrier's words, " le peu de saillie des ossicules 

 dorsaux qui sout a peine distinctes," but they are, at any rate, just 

 as clear as they are in O. granulosus, and, indeed, they are much 

 more so, while there are specimens of 0. gracilis in which the lophial 

 line is no more distinct. M. Perrier proceeds, " Les aires poriferes sont 

 larges, confluentes et paraissent meme parfois envahir toute I'eten- 

 due du disque." In young specimens the poriferous arese are 

 much more distinctly marked off than in O. aheolatus ; if there is 

 any disadvantage to the side of O. armatus with respect to its alveo- 

 lation, when adult, it is no doubt to be correlated with its better 

 development of long defensive spines. It is not always the case 

 that the spines of species of true Oreasters, according to M. Perrier — 

 take, for example, his own species 0. aheolatus- — are always free of 

 granules at their tip ; we find so many intermediate stages between 

 a complete investment and an almost complete absence of granules 

 that this character, again, must not be regarded as having, at the 

 utmost, more than a specific character. 



The species may be defined in the following terms : — 



R= T/ r to 2*1 r. Disk not high, arms very short, interbrachial 

 angles rounded ; lophial and apical spines very strong, intermediate 

 spines and spines on marginal plates exceedingly well developed ; 

 spines likewise developed on the ventral plates. 



Nine plates in the supero- and nine in the inferomarginal series ; the 

 latter all bear spines, which are short in the angles and of a moderate 

 size near the distal ends of the arms ; the three or four spines found 

 on the distal plates of the superomarginals are much larger ; the 

 superomarginals are greatly elongated from above downwards in the 

 angles of the arms, where they almost shut off the inferomarginals 

 from any share in forming the sides of the arm ; further out the 

 plates become shorter, but the penultimate is very large and convex. 



Ambulacral spinulation diplacanthid ; three or four fairly de- 

 veloped spines in the lower, and one much larger in the outer row. 

 The ventral ossicles covered with rather coarse granules, and each 

 having, rising from its centre, a blunt stout spine ; some large 

 valvular pedicellarise are developed on these plates ; the granules on 

 the inferomarginals are only a little less coarse than those on the 

 ventral ossicles, but the greater number of those on the supero- 

 marginals are much more delicate ; pedicellarise are only feebly de- 

 veloped. With increasing size the boundaries between the poriferous 

 areas become largely obliterated ; just at the interradial angles, 

 however, the ossicles are stouter in older than in younger specimens. 



The lophial spines are strong and sharp in the adult ; between 

 them some few spines may become developed ; and in the centre of 

 the apical region there is a spine as long or nearly as long as the 

 apical. A few pedicellarise are developed on the dorsal surface, the 



