ECHINOIDEA. I. 



This species has been so often mentioned and partly carefully described, that I do not think 

 there is any reason to describe it here again; so I shall only make some observations with regard to 

 a few separate features that have not before been described with sufficient exactness, viz. the arran- 

 gement of the tubercles, the pedicellariae, the spicules, and the structure of the spines. 



The interambulacral area: Round each areole there are nearest to the edge about 15 small 

 tubercles with distinct articular head, and outside of these a new circle of tubercles a little smaller 

 and situated in the intervals between the inmost ones. Outside of these are found more or fewer small 

 tubercles according to the size of the animal, decreasing in size inward towards the median line of 

 the area and outward towards the adjoining ambulacral area. The tubercles do not reach quite to the 

 median line or to the pore area; a little naked space is left, and this --at all events in larger speci- 

 mens is furrowed by irregular transverse furrows crossing the median line from one plate to the 

 other as also the line of separation between the ambulacral and the interambulacral area; the latter 

 correspond rather exactly to the lower end of each ambulacral plate. The edges round the highly 

 depressed areoles are high, the plates slope rather abruptly down towards the median line and out- 

 ward towards the pore area (PI. VI. Fig. 7). 



The ambulacral area (PI. VI. Fig. 8). Inside the pores a little tubercle is found on each plate; 

 these tubercles form a fine, regular row down each side of the ambulacral area, as is commonly the 

 case in the Cidarids; the primary series it is here called. Inside of this series still a smaller tubercle 

 is commonly found on each plate, just opposite to the outer one; nearest to the apical area and the 

 peristome the inner tubercle is commonly found only on one side, alternately -- but irregularly --to 

 the right and the left, and sometimes there is all the way down only a single series of these secondary 

 tubercles. In young specimens they are only found on the middle part of the area, and only a 

 single series; sometimes the small spines of these tubercles in the median line of the area raise per- 

 pendicularly; generally they lie over or between the bases of the primary ambulacral spines. --It is, 

 no doubt, for want of place that these secondary tubercles appear only in a single series in small 

 individuals and on the narrow actinal and abactinal end of the area in large individuals. It is espe- 

 cially on the base of these spines that the peculiar, gland-like ampulla (PI. VIII. Fig. 14) is found 

 highly developed, which has been more nearly examined by Prouho (327. p. 56) and Hamann (184. 

 p. 28). It is also often much developed on the spines of the apical area. 



A transverse section of the large spines (the radioles) (PI. XI, Figs. 14, 31) shows that in the 

 intervals between the crests the outer layer runs out in short, branched thorns that coalesce and form 

 a coarse reticulation. There is no reason to describe the form of the spines here anew. 



Although the pedicellarise of this species have been figured several times, I nevertheless think 

 it necessary to figure and describe them anew. Perrier's figures are neither good nor exact; the 

 same may be said of the figures given by Agassiz (Revision of Echini. PI. XXIV) and Koehler 

 (217. PI. 7) -- neither of them give an exact representation of the finer structures that are of systematic 

 importance. Stewart (379) on the other hand has given some excellent figures of the large globi- 

 ferous pedicellarise, and Wyv. Thomson (395) gives rather good figures of the small globiferous pedi- 

 cellarise and of the tridentate ones. - - I think it unnecessary to give a full description of the pedi- 



