REPOKT ON THE ASTERoIDEA. 



485 



Choroloyical Synopsis of the Species. 



1. Marsipaster spinosissimus, Sladen (PI. LXXVIII. figs. 5 and 6; PI. LXXIX. 

 figs. 7-9). 



Marsipaster spinosissimus, Sladen, 1882, Journ. Linn. Soc. Lond. (Zool.), vol. xvi. p. 203. 



Marginal contour pentagonoid. Pays somewhat produced. Interbrachial arcs widely 

 rouuded, forming a continuous curve from tip to tip. The minor radius is in the propor- 

 tion of 62'5 per cent. R = 16 mm. ; r = 10 mm. General form depressed; abactinal 

 area slightly convex, tapering off gently to the extremity of the rays. 



The supradorsal membrane is very fine and thin, somewhat irregular, and forming a 

 continuous spongiose mass, rather than a definite membranous sheet, through which the 

 spiuelets of the paxillse protrude freely. No specialised muscular fibrous bands are present. 

 The spiracula, which are very few in number, are widely and irregularly spaced. 



The paxillse have long pedicles and a crown consisting of a great number of very fine 

 hair-like spinelets (twenty to thirty at least upon the disk), which radiate at a small angle 

 from the perpendicular, the crown and pedicle being alike invested with a delicate mem- 

 branous tissue, the whole appendage seen in profile bearing a fanciful resemblance to an 

 umbrella when turned inside out. The investing membrane merges into the general spongy 

 tissue above mentioned, and a considerable length of the extremities of the spinelets pro- 

 trudes free and naked. The paxilla? are numerous, and their crowns join up close together. 

 Owing to these circumstances and to the great number of the spiuelets, the abactinal 

 surface presents the appearance of a coarse, irregular velvet pile. The oscular orifice is 

 small and quite inconspicuous, the valves consisting of a flattened crown of rather more 

 robust spinelets. 



The ambulacral furrows are rather broad, not petaloid, and taper towards the extremity. 

 The tube-feet are arranged in simple pairs. The armature of the adambulacral plates 

 consists of five long, acicular spinelets, webbed together into transverse or obliquely 

 curved combs, and remarkable for their position more than half within the furrow. The 

 spines are of unequal length, the innermost being much smaller than any of the others, 

 aud placed somewhat in advance of, or aboral to, the series ; the longest spine, which is 



