216 MR. W. PERCY SLADEK ON THE 



At the base of each valve is a rather close aggregation of paxillse- 

 spinelets, whereby a more or less complete annulus is formed 

 around the orifice ; and from each of the five groups in question 

 proceed a number of spinelets, which i-adiate outward from the 

 centre and constitute a conspicuous feature. 



Ambulacral furrows very wide, subpetaloid, tapering to a fine 

 extremity, and constricted slightly near the actinostome. Ambu- 

 lacral spines, only one to each plate, long, cylindrical, tapering to 

 a fine point, and placed on a small process projecting into the 

 furrow. Aperture-papilla elongate, covered with very widely ex- 

 panded membrane, imparting an acumino-spatulate form. 



The mouth-plates are long and thin, the pair having the ap- 

 pearance of being pressed together laterally, projecting aborally 

 in a prominent rounded keel, and sloping ofi" somewhat plough- 

 share-like towards the mouth. Two spinelets, similar to the 

 general ambulacral series, only perhaps rather shorter, stand on 

 the superficies of each plate, one on the sloping curve leading to 

 the adoral margin, and one aboral to this and more outward in 

 relation to the median suture-line of the plates. These spinelets 

 appear greatly modified both in character and position from the 

 usual robust secondary spinelets of the genus. The mouth-spines 

 are represented by two spinelets, similar in all respects to the 

 ambulacral spines, only rather shorter, placed on the horizontal 

 margin of each plate, and close up to the junction with the first 

 adambulacral plate. 



Actino-lateral spines very long, the longest being about the 

 15th from the mouth. In the inner part of the ray they are 

 comparatively delicate, when regard is had to the size of the spe- 

 cimen — increasing, however, in robustness as they proceed along 

 the ray, those near the angle and the succeeding ones being strong 

 and thick. The spines reach quite up to the median line of the 

 interbrachial area ; indeed in the outer half they pass beyond and 

 overlap ; whilst the longest spines, which fall in the actual arm- 

 angle, are much longer than the distance between the median 

 interbrachial line and the margin of the furrow. In consequence 

 a prominent outward peak is produced in the place of the angle, 

 the web being much contorted, and an abnormal growth not un- 

 frequently taking place, which produces an unsightly excrescence 

 as well as an irregular thickening of the tissue. The outer ex- 

 tremities of the actino-latt;ral spines are not pointed, but rounded ; 

 and the web-tissue is scarcely indented. Owing to the abnormal 



