REPORT ON THE ASTEROIDEA. 485 
Chorological Synopsis of the Species. 
| Ocean. | Range in Fathoms. Nature of the Sea-bottom. 
| nse ees : s ee ee 
| - 
Marsipaster alveolatus . ; | Atlantic. | 2192 
| 
| Marsipaster hirsutus — . ond | Pacific. | 2160 Blue mud. 
Marsipaster spinosissimus —, | Pacific. | 2339 Red clay. | 
1. Mursipaster spinosissimus, Sladen (Pi. LXXVIII. figs. 5 and 6; Pl. LXXIX. 
figs. 7-9). 
Marsipaster spinosissimus, Sladen, 1882, Journ. Linn. Soc. Lond. (Zool.), vol. xvi. p. 203, 
Marginal contour pentagonoid. Rays somewhat produced. Interbrachial arcs widely 
rounded, forming a continuous curve from tip to tip. The minor radius is in the propor- 
tion of 62°5 per cent. R= 16 mm.; 7=10mm. 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 
spinelets of the paxillee protrude freely. No specialised muscular fibrous bands are present. 
The spiracula, which are very few in number, are widely and irregularly spaced. 
The paxille 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 paxille are numerous, and their crowns join up close together. 
Owing to these circumstances and to the great number of the spinelets, 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, 
and placed somewhat in advance of, or aboral to, the series ; the longest spine, which is 
