28 THE TERTIARY FOSSIL ECHINOIDEA 



it is more broadly rounded, but posteriorly it becomes slightly flattened at the spot 

 corresponding with the periproct. The highest point of the test is central, and there 

 is a sharper slope forwards than backwards. The margin is boldly curved and tumid 

 in front, and the tumidity diminishes behind the antero-lateral ambulacra, where the 

 test is rather sharply rounded ; and this condition persists to the neighbourhood of the 

 periproct. 



The apex is rather excentric in front, being 9 millim. in front of the centre, the 

 extreme length of the test being 77 millim, ; and the result is to give a comparatively 

 narrow anterior part and a long and broad posterior portion. The sunken peristome is 

 excentric in front and under the apical system, and is surrounded by the tumid actinal 

 surface ; and the test rests on a surface between the peristome and the ambitus. There 

 is slight flattening between the peristome and the periproct. 



The apical system is small, the disk is round, and the ocular pores hidden. 



The ambulacra, unequal in length, are on the whole narrow, and nearly flush with the 

 test ; the antero-lateral ambulacra curve slightly, concavity in front, are very wide apart, 

 and tend decidedly to close ; but the anterior poriferous zone is shorter than the other, 

 and curves slightly backwards at its termination. The posterior zone is curved with 

 the concavity forwards, and near the margin it ends with a slight curve in the opposite 

 direction. The zones are narrow and about one half of the breadth of the inter- 

 poriferous areas where best developed. The inner series of pores are circular in outline, 

 and the outer are larger and elongate-elliptical ; they are conjugate, the groove being 

 slightly oblique, and the costae, which are well developed, have a row of granules. 



The postero-lateral ambulacra form an angle of about 7Q°, are straight, slightly 

 broader in the interporiferous zone than the anterior, reach far towards the margin, but 

 not more so than the antero-lateral, are widely open, and there is one pair of pores in 

 excess in the anterior zone. The poriferous zones are slightly narrower than those of 

 the antero-lateral ambulacra, and the conjugating grooves are more oblique. 



The postero-lateral interradia are slightly gibbose at the niargin, and the posterior 

 interradium is flattened behind the periproct. 



The peristome is large, broad, pentagonal, with the nearly flat bourrelets subequal 

 in the antero-lateral and posterior interradia, and narrowest in the postero-lateral regions. 

 The pores are sunken in round pits, and the reduplication is scanty. The walls of the 

 peristome pass up and form a pentagonal tubular process with the angles rounded. 



The periproct, broader than long, has a slightly curved posterior and a more boldly 

 curved anterior margin, and the junction of the margins is by acute lateral angles. 

 A mere ridge separates it from the posterior surface of the test. 



The ornamentation is generally close, and is larger actinally than abactinally ; that 

 of the interporiferous zones is similar to that of the interradia. It consists abactinally 

 of small depressed tubercles with small pointed mamelons, both crenulate and perforate, 

 standing in shallow circular scrobicules which are separated by a slightly raised surface 

 crowded with distinct and sharp granules. Just under the ambitus the crowded orna- 

 mentation is the smallest, and the largest kind is found on the bourrelets and on the 



