24 THE TERTIARY FOSSIL ECHINOIDEA 



where there is a very slight narrowing of the interporiferous zone and a decided dimi- 

 nution in breadth of the poriferous zones. The poriferous zones are narrow ; about 2^ 

 their breadth would equal that of the interporiferous at the widest part ; the inner pores 

 are circular and large ; and the outer, elongate elliptical, are equal to or even slightly 

 larger than the others ; a broad and deep groove connects them ; and the costse between 

 the pores are stout, rounded above, where there is a row of distinct granules. The 

 direction of the costse and grooves is rather oblique. The breadth of the zone diminishes 

 marginally, but there is only a slight difference in the respective zone-lengths. The 

 ornamentation of the interporiferous zone is of numerous sunken tubercles in scrobicules 

 rather more than their own width apart. The tubercles are slightly mammillated and 

 crenulate, and the interscrobicular areas are rather tumid and sharply and distinctly 

 granular. 



The antero-lateral ambulacra form a very wide angle, have the posterior poriferous 

 zones more bowed than the anterior, and there are a few more pairs of pores in the 

 anterior than in the posterior zone. 



The postero-lateral ambulacra are sinuous, and the anterior poriferous zone is 

 slightly the longest. The poriferous zones are continued in all the ambulacra over the 

 margin to close to the peristome as a single series of pores. 



The interradial areas abactinally are very faintly tumid near the apex, have a 

 distinct median sutural line, and there is a slight flattening of the posterior interradium, 

 with two indistinct keels running down to the margin to end on either side of the 

 periproct. 



The ornamentation is equal from just above the margin to the apex, and consists of 

 the same structural details as seen in the interporiferous ambulacral areas. The granula- 

 tion, however, is distinct and large, but scanty. Near the margin the scrobicules become 

 much closer, and thence to the peristome the ornamentation is less crowded, but more so 

 than above. Near the periproct it is crowded, and especially at the posterior margin, 

 where it is smaller than elsewhere. Between the periproct and the peristome is a worn 

 surface. 



The peristome is subcentral, and not quite beneath the apical system in some and 

 beneath it in others. It is large, widely open, elongate transversely, pentagonal, and 

 the bourrelet of the posterior interradium is low and the broadest; those of the 

 anterior interradial areas are slightly tumid and project, and are larger than those of the 

 lateral areas. A minute tuberculation covers the ingoing process from the peristome ; 

 and the rudimentary phyllodes are in very shallow grooves. There is a well-developed 

 row of outer pores in each phyllode and a few inner ones, but they are between 

 the plates on the sutural lines. The usual pair of pores is at the commencement of 

 each phyllode within the peristome ; and there are numerous pits in the position of 

 sphseridia. 



The periproct is larger than the peristome, is elongate transversely, and irregularly 

 elliptical, the posterior curve being less than the anterior. It is inframarginal, and not 

 visible from behind. 



