302 HIPPONOE ESCULENTA. 



which, from the ambitus to the abactinal pole, is more or less bare, the 

 coronal plates are covered by miliaries. The third vertical row, count- 

 ing from the poriferous zone, is the most prominent one, this and the 

 adjacent one internally (towards median line) being the only ones to 

 reach the abactinal system. The tubercles, as a general tiling, are very 

 uniform in size, except in specimens where much of the median line is 

 bare, when the contrast between the main row (the third) and the other 

 is more marked, more like primary and secondary. On the lower surface, 

 both of ambulacral and interambulacral spaces, the tubercles are very uni- 

 form in size and closely packed in concentric rows round actinostome as 

 centre. The median ambulacral space is filled by five more or less dis- 

 tinct vertical rows, quite marked at ambitus, central row indefinite, exterior 

 being more prominent, also tending to arrangement in horizontal rows; the 

 vertical lines of pores are separated by irregularly arranged vertical rows 

 of secondary tubercles forming from two to three vertical lines. 



Abactinal system well marked, madreporic body larger than others. 

 Three ocular plates excluded from large anal system covered bj- a com- 

 paratively small number of plates of nearly uniform size, very few smaller 

 ones immediately round anus, each plate carrying but one or two small 

 secondary tubercles and few miliaries, the genital ring having but few 

 secondary tubercles; near anal system they are more numerous, but also 

 sparsely scattered over the rest of the genital and ocular plates. The 

 actinal opening is small, with deep cuts; membrane covered by minute 

 plates irregularly scattered, not closely crowded. Spines short, compara- 

 tively stout, Color of spine whitish or yellowish, test generally brownish, 

 the median line frequently (interambulacral space) colored a beautiful violet. 

 Young specimens in which the median interambulacral and ambulacral space 

 are comparatively very bare have been described by Girard as Heliechinus. 

 The central vertical line of pores of the poriferous zone is slightly nearer the 

 inner line, though frequently almost in middle. 



Heliechinus Gouldii of Girard (PL VI a . f. J), of which the original is in 

 the Museum collection, is nothing but a young Hipponoe esculenta. In 



