FROM THE INFERIOR OOLITE. 205 



with a larger one (fig. 1 c) ; the tubercles of the ambulacra are smaller than those of the 

 inter-ambulacra ; they are raised on small bosses, and surrounded by depressed, ring-shaped 

 areolas (tig. 1 c), which are bounded on one side by the poriferous zones, and on the 

 other by a row of small lateral granules ; between the two rows of granules there is a 

 naked space (fig. 1 c), in which the suture is distinctly seen ; towards the base of the area 

 this space is filled with other rows of granules, and from four to six large tubercles, which 

 extend round the angle to the base (fig. 1 5), where the marginal tubercles are disposed 

 with great regularity, surrounded on each side by trigeminal ranks of pores, which lie at 

 angles of 20° across the wide zonal space (fig. Id). 



The poriferous zones are of a uniform width on the sides; they are slightly contracted 

 at the angle, and again expand at the base ; the trigeminal ranks of pores are disposed 

 very obliquely across the zones, at angles of from 30° to 40° ; there are three small 

 granules between each rank (fig. 1 c), and each pair of pores is surrounded by an oval 

 elevation of the test ; the pores of each pair are placed obliquely upwards, and there are 

 about five trigeminal ranks opposite every two large plates, which, estimating twenty-eight 

 plates in a coluuni, gives about seventy triple obhque pairs of pores in each zone. 



The inter-ambulacral areas are three times the width of the ambulacral ; they are 

 composed of long, narrow, pentagonal plates, of which there are twenty-eight in each 

 column of an adult shell ; each area has two rows of primary tubercles in the centre of the 

 plates, which extend from the peristome to the apical disc (fig. 1 a) ; between this row and 

 the poriferous zones there are two rows of secondary tubercles, which become rudimentary 

 half way up the sides ; between the primary row and the centro-suture there is another 

 short row of six or seven secondaries (fig. 1 a, c) ; the tubercles are raised on small bosses, 

 which are surrounded by depressed areolas, and the granules of the miliary zone form 

 complete circles around them. 



On the upper half of the area there is a well-marked median depression, which divides 

 it into halves ; the depression is naked, but the rest of the wide inter-tubercular space is 

 covered with numerous granules (fig. 1 a). 



The marginal fold in this species forms an acute angle ; the base is concave, and 

 crowded with large tubercles, the secondaries being as large as the primary rows in this 

 region of the test (fig. I b). 



The mouth opening is very large, nearly one half the diameter of the base ; the 

 peristome is pentagonal, with two wide and deeply incised notches at each angle, opposite 

 the base of the inter-ambulacral areas (fig. 1 b) ; between these the short lobe is rounded, 

 and the margins of the large ambulacral lobes form double curved lines (fig. T b, d). 



The apical disc is small and excentral; it is placed backwards, and projects into the 

 single inter-ambulacrum ; the genital plates are very narrow, the anterior pair being 

 larger than the posterior pair ; the right antero-lateral plate, with the prominent spongy 

 raadreporiform body, is the largest, and the posterior single plate the smallest ; the 

 oviductal holes are pierced near the apex ; the ocular plates are small and heart-shaped. 



