8 THE FOSSIL ECHINOIDEA 



Interambulacral areas wide, usually three or four times the width of the 

 ambulacral areas, with two vertical rows of primary tubercles. Primary tubercles 

 large, perforate or imperforate, crenulate or non-crenulate, rising from a circular or oval 

 scrobicule, surrounded by a scrobicular ring of miliaries. 



Apical system large, subcircular. 



Peristome subcircular, without notches. 



Spines elongate, robust, very variable in form and ornamentation. 



1. CiDAEis LACETMULA, sp. nov. Plate I, Figs. 1-7. 



Form circular, depressed, tumid at the ambitus, and smaller above than below, 

 where there is considerable flattening. Height of the test about one half of the 

 diameter. 



Ambulacra rather broad and slightly flexuous. Poriferous zones broader than 

 half the interporiferous area, and slightly sunken. The pores are large and 

 transversely elliptical, non-conjugate, being separated by a vertical and convex process, 

 which externally resembles a compressed granule ; this merges aborally and adorally 

 into the general superficies of the plate, which is continued around the pores in more 

 or less of a ridge. There are 26 to 27 pairs of pores in relation to two of the largest 

 interambulacral plates. The interporiferous (ambulacral) areas are narrow, and have 

 at the ambitus two rows of small mamillated tubercles placed close to the pores, and 

 two rows of very small tubercles (miliaries) between them. Near the apex and 

 actinostome these central small tubercles are not seen. 



The interambulacral areas are about three times the width of the ambulacra at 

 the ambitus; and there are two rows, of six to seven primary tubercles, in each 

 interambulacrum. 



Primary tubercles moderately prominent ; mamelons rather small and somewhat 

 depressed, not crenulated. Scrobicules wide, circular, occupying much of the plate, 

 and only slightly sunken ; the tubercle not greatly elevated, surrounded by a complete 

 circlet of small mamillated tubercles, the boss being somewhat shield-shaped, with 

 the truncate margin falling into the scrobicular circle, and the mamelon more or less 

 tear-shaped, the tapering extremity beiag directed inwards towards the primary 

 tubercle. There are about thirteen of these secondary tubercles in the ring ; and 

 between each of them alternates a small simple tear-shaped miliary tubercle, with the 

 fine extremity pointed inwards. The miliary zone is narrow, naked along the suture, 

 and slightly impressed, the ornamentation consisting of one or two series of small tear- 

 shaped granules which are placed external to, and alternate with, those of the 

 scrobicular ring above mentioned. On the aboral and adoral margins of the inter- 

 ambulacral plates, however, there is only room for the accommodation of the granules 

 of the scrobicular ring ; and as the plates approach the actinostome the adoral margin 

 even of this is more and more encroached upon. On the side, between the ring and 

 the poriferous zone, there is seldom more than a single series of the small miliary 

 granules supplementary to those of the ring. 



Peristome rather small, margins more or less inturned. Apical disk comparatively 



