254 



ME. W. PEEOT SLA.DEN ON THE 



bent; the second, whicli stands immediately behind, is about 

 two thirds the length and precisely similar ; the third spine is very 

 small, not more than one third the length of the preceding, and 

 is hardly worthy of being ranked as a marginal spine. Some- 

 times a small spinelet similar to the last mentioned stands by 

 the side of the second marginal spine. Ko other spinelets are 

 present on the infero-marginal plates excepting a single isolated 

 spinelet in the median line and near the inner end of the plate adja- 

 cent to the adambulacral plates. This spinelet is cylindrical, taper 

 and sharply pointed, and somewhat longer and more robust than 

 the third marginal spine ; its presence and isolation gives a very 

 characteristic appearance. The surface of the infero-marginal 

 plates is covered with small and not very closely crowded papil- 

 liform squamules, which increase slightly in length and robust- 

 ness at the inner end of the plate near the adambulacral plates. 



Ambulacral spines not very large or prominent. Innermost 

 furrow-series three in number, delicate, cylindi'ical, taper ; the 

 middle spine slightly more prominent in the furrow than its 

 companions. Outer spinelets difficult to formulate, in conse- 

 quence of irregularity in their mode of arrangement. JSTormally 

 a second and an outer series are present, having about three 

 spinelets in each ; but these are often placed in such a way as to 

 appear to give two to the second series and four, arranged dia- 

 mond-wise, to the outer series ; frequently, also, one or two small 

 additional spinelets may be present, usually in the latter series, 

 which then forms a group. The second series are shorter than 

 the inner series, and are slightly compressed and faintly sub- 

 spatulate. The outer spinelets are shorter than the preceding 

 and are not flattened ; their length near the middle of the ray is 

 very slightly in excess of the length of the papillif orm squamules 

 of the adjacent ventro-marginal plate. Very few ventral plates 

 are present, and bear spinelets similar to the outer ambulacral 

 spines, and these are usually grouped together into an incipient 

 pedicellaria (?). 



Mouth-plates elongate, and covered with comparatively long, 

 closely-placed spines, which are flattened and more or less sub- 

 spatulate. The two inner spinelets, placed side by side on each 

 plate, are longer and larger than the rest ; and these, together 

 with their smaller lateral companions, form a horizontal comb of 

 6-8 spinelets directed towards the centre of the mouth. Beliind 

 these inner spinelets follow two or three shorter spines in lineal 



