REPORT ON THE ASTEROIDEA. 137 



The madreporiform body is large and conspicuous, subcircular or oval in form, and 

 situated in an interradium close up to the supero-marginal plates, and consequently 

 adjacent to the cribriform organ. Sometimes it is subtriangular in contour, with 

 the base directed to the margin, and the striae form lines sharply bent at an angle, 

 running more or less parallel with the sides of the triangle, the open angle being 

 directed towards the base. 



Colour in alcohol, yellowish white, with a bluish-grey shade over the disk. The 

 marginal plates and the actinal interradial areas have a peculiar glazed appearance, 

 consequent on the character of the investing membrane. 



Individual Variation. — A very slight amount of difference may be noticed in a series 

 of specimens in the height of the lateral wall of the ray ; and in some specimens the 

 marginal plates stand rather more vertical, and are less arched towards the abactinal 

 surface. In some specimens the small conical spinelet or tubercle on the upper margin 

 of the supero-marginal plates is more strongly developed than in others ; and in other 

 examples it is absent altogether from some plates here and there, perhaps owing to 

 abrasion. In some examples a very minute thornlet may be seen occasionally on an 

 intermediate plate here and there in the actinal interradial area. In one specimen a third 

 spinelet is present on some of the adambulacral plates, usually about the middle of the 

 ray or near the mouth. 



In some examples the rays are rather broader at the base than in others, and 

 this is especially noticeable in a large example from Station 46 ; in others they are 

 longer and more attenuate throughout. 



Locational Variation. — The specimens from Station 45 appear to be of a rather 

 smaller size than those from other Stations ; the rays also are narrower, and the small 

 spinelet on the supero-marginal plates is slightly more delicate and spine-like than in 

 specimens of the same size from Station 47. 



On the whole, however, I am by no means certain that these slight modifications 

 can be correctly ranked as locational variations in preference to individual variations ; a 

 much larger supply of material would be necessary to decide the point than I have 

 had at my disposal. 



Young Phase. — The smallest example, unquestionably belonging to this species, that 

 I have seen, measures R = 8 mm. ; r = 4 mm., approximately ; and it already presents 

 the characters of the adult in a remarkable manner. I have no hesitation in referring it 

 to the species. The abactinal membrane is very thin, and the spiniferous spicules are 

 confined to definite areas which traverse the interradial lines. The anal funnel is well 

 developed. There are four supero-marginal and four infero-marginal plates, and traces 

 of a small fifth plate are visible, the infero-marginal one being the most developed, and 

 appears to be the first formed. The cribriform organs are large and conspicuous. The 

 adambulacral plates bear two short conically pointed spinelets. The mouth-plates have 



(ZOOL. CHALL. EXP. — PART LI. — 1887.) IS 



