RETORT ON THE ASTEROID EA. 17 



than two-thirds its length, stands close to the lateral spine on the inner side, and is 

 likewise articulated on a tubercle. The surface of the plate is covered with membrane, 

 and there are a few widely spaced miliary thornlets on the vacant areas on each side 

 of the spines. On the inner part of the ray, and especially on the innermost plates in 

 the interbrachial arc, these assume the form of short, cylindrical, obtusely tipped 

 spiuelets. Occasionally also one of these near the base of the second lateral spine is 

 longer than the rest, and then simulates a third (but very small) member of the infero- 

 marsrinal armature. 



In the median interradial line is a large and broad odd infero-marginal plate, corres- 

 ponding to the odd supero-marginal plate. Its position is vertical, and this plate as 

 well as the two next plates on either side bear no large lateral spines, but only two 

 or three short aborted cylindrical spinelets and a few miliary spinelets or thornlets. 



Between each successive infero-marginal plate is a rather large pedicellarian apparatus, 

 at least along two-thirds the length of the ray ; these are of the double comb or spiracle 

 form, and consist of five or six short tapering spinelets borne on each of the adjacent plates, 

 the two series being opposed to one another, and closing over the intervening cavity. The 

 apparatus occupies nearly the whole of the vertical margins of the plates and comes close 

 to the actinal margin. 



The adambulacral plates are large, broad, and well-spaced, the breadth being slightly 

 greater than the length. There is a small semicircular prominence into the furrow ; and 

 the armature consists of : — (1.) a furrow series of six to eight very small, short, cylindrical, 

 obtusely tipped spinelets, all equal excepting the outermost at each end of the series, 

 which are rather shorter. All are placed close together, and form a compact semicircular 

 comb, the spinelets, when directed vertically, standing parallel to one another, and when 

 directed over the furrow, radiating slightly apart. The successive combs are well spaced 

 apart. (2.) On the actinal surface of the plate are three comparatively elongate, 

 cylindrical, obtusely tipped spinelets, placed one behind the other in an oblique line, the 

 outermost being usually smaller than the others, sometimes wanting, sometimes irregularly 

 placed, and absent at the extremity of the ray. The longest of these spines is about 

 2"5 mm. ; the marginal series not exceeding 1 mm. in length. No other spines or 

 thornlets are present on the plate, and its surface is covered with membrane. 



The ambulacral furrow is widely open, and the tube-feet are large, conical, and with 

 a small knob-like termination. 



The mouth-plates are large, prominent and convex actinally, the united pair being 

 broad, with a flattened semicircular margin towards the actinostome. Their armature con- 

 sists of a marginal series of six or seven mouth-spines on each plate, the innermost one being 

 twice or three times the length and robustness of the others, which are subequal, all 

 being cylindrical and obtusely tipped. On the actinal surface of the plate are three short, 

 cylindrical, obtusely tipped spinelets, rather smaller than tbe actinal spines on the 



(ZOOL. CHALL. EXT. PART. LI — 18S7.) 3 



