FROM THE INFERIOR OOLITE. 233 



genus. This is not the only example among fossil Echinodermata illustrative of the fact, 

 that the first created forms of new types of life are often the most characteristic of the 

 group they represent; the figure and description of the first species of every genus 

 contained in this Monograph is, in fact, a practical commentary on this great natural law. 



The ambulacral areas are narrow, straight, and prominent; they have two rows of 

 small, well-developed tubercles, from twelve to fourteen in each row, disposed on the 

 margins of the areas, which gradually diminish in size from the base to the apex 

 (fig. \ a,b); a zigzag line of small granules descends down the centre, sending lateral 

 branches between every two tubercles ; this granular network encircles three parts of the 

 areolas, and leaves them open only to the poriferous zones (fig. 1 d) ; the tubercles at the 

 base of the area (fig. 1 b, e) are large, and remind us of the semi-tubercles in this region 

 in Hemicidaris. 



The poriferous zones are narrow ; the pores are unigeminal, except at the base, where 

 they fall into oblique ranks of threes (fig. 1 e) ; there are eleven pairs of pores opposite 

 two large plates (fig. 1 d). 



The inter-ambulacral areas are three times and a half as wide as the ambulacral ; there 

 are eight tubercles in each row, which, at the circumference, are raised on very large 

 prominent bosses (fig. 1 a, c) ; one of these mammae, drawn in profile (fig. 1/), shows its 

 conical form ; it is surrounded by a wide, oval areola (fig. 1 d), which is confluent with its 

 fellow above and below ; the tubercles are large at the base, but suddenly diminish in size 

 in the upper part of the area ; there are ten crenulations on the summits of the bosses, 

 and the tubercles are small in proportion to the magnitude of these eminences ; the two 

 rows of tubercles are separated by a zigzag granular band, or miliary zone, in the centre 

 of the area (fig. 1 c), consisting of two rows of granules, and a few additional smaller ones 

 dotted here and there in the interspaces ; similar crescentic bands of granules separate the 

 areolas from the poriferous zones ; each plate, therefore (fig. 1 d), has a semi-circular row 

 of granules, with a few granulets, on its central side, and a similar row on its zonal side, 

 whilst the upper and lower borders are destitute of sculpture. On the upper part of the 

 area the granules disappear, and leave a small, naked, median depression between the three 

 uppermost pairs of small tubercles (fig. 1 a). 



The base is flat, or slightly concave (fig. I c) ; the mouth opening is large, one half the 

 diameter of the test ; the peristome is decagonal, and divided by wide notches into 

 unequal-sized lobes, the ambulacral being one half larger than the inter-ambulacral lobes 

 (fig. 1 b), and its margin is folded over at the angles of the notches (fig. 1 c). 



The small apical disc is very seldom preserved ; fortunately I lately found one 

 specimen with most of the plates in situ (fig. 1 a), and another with the sur-anal plate, 

 which is single, or more probably composed of three plates soldered together ; it is the 

 only specimen I have seen with this portion of the disc, the coarse character of the Pea-grit 

 in which they are found being unfavorable for the preservation of this fragile and complex 

 part of the shell. 



