RETORT ON THE ASTEROIDEA. 179 



along the ray, but is considerably greater in the interbrachial arc, where the border 

 formed by the infero-marginal plates occupies very nearly half the space between the 

 mouth-angle and the margin ; on the outer part of the ray the proportion of breadth to 

 length diminishes gradually, but the breadth remains preponderant throughout. The 

 surface of the plates is faintly but flatly convex, emphasized by the rounded bevel at the 

 margin of the well-defined transverse channel between each successive plate. The surface 

 of the plates is covered with uniform, well-spaced, hyaline, deciduous, hemispherical 

 granules, similar to, but perhaps slightly smaller than, those on the supero-marginal 

 plates, and the margins are furnished with a similarly webbed fringe of small spinelets 

 directed horizontally over the transverse channels between the plates, the fringe increasing 

 a little in breadth as it approaches the edge of the ray. On the infero-marginal plates 

 which abut against adambulacral plates, the fringe is not present on that edge, but the 

 four innermost infero-marginal plates, that is to say, two on each side of the median 

 interradial line, which abut against the actinal intermediate (ventral) plates, have the 

 fringe continuous round the inner end of the plates, and on a few plates next succeeding 

 a trace of the fringe is discernible, the abortion being effected gradually. Each infero- 

 marginal plate bears a single, small, compressed, comparatively broad, flat, truncate spine- 

 let, scarcely longer than the length of the plate ; it is articulated but adpressed to the 

 ray, directed towards the extremity at a slight angle upwards, and it is placed at the 

 extreme margin of the actinal surface, consequently a little below the upper edge of the 

 infero-marginal plate, and stands close to its aboral margin. Occasionally on one or two 

 plates in the interbrachial are a second smaller and very much narrower spiuelet may be 

 present at some distance from the marginal one, on the actinal surface, and likewise close 

 to the aboral margin of the plate. 



The adambulacral plates are small, and, as seen with their armature when viewed 

 from above, appear subquadrate or rhomboid in form. Their armature consists of a 

 furrow series of five or six short, cylindrical, slightly tapering spinelets, the outer ones 

 rather smaller than the others, and all radiating slightly apart at au angle over the 

 furrow. The actinal surface of the plate is covered with membrane, and is devoid of 

 spinelets, but bears round its margin, that is to say, on the three remaining sides, a series 

 of small, uniform, skin-covered, papilliform, obtuse spinelets, very much shorter than the 

 furrow series, and directed at an angle of about 45° to the plane of the plate, towards the 

 adjacent plate, whether this be an adambulacral or marginal one. There is thus the appear- 

 ance of a straight channel intervening between the series of adambulacral plates and the 

 marginal plates over which the series of skin-covered spinelets is directed, and the adam- 

 bulacral plates are themselves distinctly and clearly spaced. Near the middle of the 

 aboral margin of each adambulacral plate is one comparatively very robust, short, stumpy, 

 subconical spinelet, its posture suggesting resemblance to a thumb in relation to the 

 furrow series of spinelets, if these were considered as the finders of an outstretched hand 



