REPOKT ON THE ASTEROIDEA. 



283 



Chorology of the Genus Chitonaster. 

 a. Geographical distribution : — 



Southern Ocean : One species between the parallels of 60° and 70" S. 



Chitonaster cataphractus, in the neighbourhood of the pack ice of 

 the Antarctic Circle, near the meridian of 95° E. longitude. 



/9. Bathy metrical range : 1975 fathoms. 



y. Nature of the Sea-bottom : Diatom ooze. 



Cliorological Synopsis of the Species. 



1. Chitonaster cataphractus, n. sp. (PL LXXIIL, figs. 1-3). 



Pays five. R = 16 - 5 mm. ; r = 5 mm. R> 3 r. Breadth of a ray between the second 

 and third infero-marginal plates, 4'75 mm. 



General form stellate. Pays well produced and tapering from the base to the extremity. 

 Abactinal area of the disk convex and almost hemispherical as seen in profile, that of the rays 

 rounded and forming with the lateral wall a uniform curvature. Actinal area subplane. 



The abactinal area is more or less rigid and entirely covered with closely-fitting 

 hexagonal, or perhaps in places partially rounded, plates overlaid with a uniform layer of 

 membrane, which renders it difficult to define exactly the outline of all the plates. Each 

 plate bears one, and occasionally two or even three, short, robust, cylindrical, obtuse 

 spinelets or elongate tubercles, uniform, and equal throughout, the membrane mounting 

 the base, but becoming so thin on the upper part that it is scarcely perceptible. No 

 definite order of arrangement of the plates is distinguishable, but on the outer part of the 

 ray only a single series of abactinal plates separates the supero-marginal plates of the two 

 sides of a ray ; and these extend uninterruptedly to the tip and are comparatively large. 

 Occasionally a small granule is present on the plates, usually near the edge. I have failed 

 to detect the presence of any trace of papulae. 



The supero-marginal plates, which are thirteen in number, counting from the median 

 interradial line to the extremity, have the height (or breadth) greater than the length, 

 and are slightly arched upon the abactinal surface in conformity with the rotundity of the 

 ray. Each plate bears normally two short, obtuse, cylindrical spinelets or tubercles, 

 similar to those on the abactinal plates, placed one above the other, that is to say along 



