some Species referred to it. 51 



(our PI. I. fig. 1). This is an iiiterambulacral plate, with 

 mamelon elongate, probably in a meridian direction, perforate, 

 the perforation similarly elongate, rising from a slight plat- 

 form, now almost entirely broken away and retaining no trace 

 of a parapet if ever there was one. The boss passes with a 

 gentle convexo-concave slope, and no trace of a basal terrace, 

 into the slightly depressed area, which is bounded by no 

 distinct rim. Tliere appears to have been a complete circle, 

 perhaps a trifle flattened above and below, of scrobicular 

 tubercles. Those on one side, to the number of four, were 

 larger than the others, were doubtless maraelonate, and 

 though much worn still show faint traces of scrobiculation ; 

 they may be called secondary tubercles. Those on the other 

 side were much smaller, more numerous, numbering 8 or 9, 

 and rather irregular in position ; they may be called tertiary 

 tubercles. Their mamelons, still clearly preserved in some 

 cases, were almost certainly imperforate, as stated by Sand- 

 berger, and in no way justify Desor's suggestion of perfora- 

 tion, wiiich was doubtless based on some obscure marking in 

 Sandberger's figure. The tertiary tubercles can be traced 

 across owq end of the scrobicule (the left in our figure), and 



Fio-. 1. 



Restored diagram of liolotype of Eocidaris Icevispina, 

 enlarged 2^ diameters. 



there is some indication that they formed a similar line at the 

 other end, but that margin is more broken away. The extra- 

 scrobicular tract adjoining the lateral tertiary tubercles slopes 

 sharply downwards, and bears three elevations (there may 

 have been a fourth, to the right in our figure). These eleva- 

 tions do not appear to be the remains of tubercles, but seem 

 rather to represent a folding or denticulation of that margin 

 of the plate. This suggests that the margin in question is 

 adambulacral, a view consonant with the position of the larger 

 (secondary) tubercles on the opposite side of the scrobicule. 

 On this evidence we may, perhaps, venture to reconstruct 

 the plate as shown in the annexed diagram (text-tig. 1). 



The original of Sandberger's fig. '2h (our PI. I. tig. 2) is 



4* 



