352 THE FOSSIL ECHINOIDEA 



The pairs of pores of the included zones are just within the fasciole, and those of 

 the outer zones are considerably beyond it. The ornamentation of these plates has 

 been noticed ; but it is to be remarked that the fasciole is made up of exceedingly 

 minute and crowded granules with a row of large ones on the edge. There is a median 

 line of small tubercles in the area, and a plain surface above it. 



The anterior interradia on the dorsum are minutely tuberculated just above the 

 margin, and still higher up a minute granulation separates some slightly larger 

 tubercles into irregular transverse lines, which are complicated in some individuals by 

 the presence of offshoots of the front part of the fasciole. The great sunken tubercles 

 are between the fasciole and the keel on the side of the anterior groove. Usually there 

 are three irregular rows of them, and one solitary tubercle is nearest the crossing point 

 of the internal fasciole and the anterior poriferous zones of the antero-lateral ambulacra. 

 There are about 13-15 tubercles in the rows in a typical adult form, and there is some 

 variation in the size of those of the same row. The smallest tubercles are in the outer 

 row and the most perfect are in the rows nearest the apex. 



A typical tubercle has a deep sunken scrobicule, departing slightly from the 

 circular in outline. The boss is much smaller than the scrobicule, rises suddenly from its 

 centre as a cylindrical cone, and comes very slightly above the general level of the surface. 

 It is capped by a small narrow perforate mamelon, which is much smaller than 

 the top of the boss, which has a wide groove around its base. On the anterior part 

 of the collar around the groove are a few close nodular processes, simulating a rough 

 crenulation ; but this condition is only found on one part of the periphery of the boss. 

 The bosses are in the middle of the scrobicules, and these have sharp edges which are 

 separated by much close granulation. The rows of tubercles in the lateral interradia 

 are longer and contain more tubercles than the anterior sets. Three rows and a solitary, 

 or, in some instances, two tubercles, are seen in the lateral interradia, and the number 

 is from 20-24. There is some variation in the size. The same kind of granulation 

 separates these tubercles as is the case in the anterior interradia. 



The posterior interradium is without tubercles on the dorsum. 



In the anterior interradia, on the actinal surface, there are some closely placed 

 tubercles, which are on the outskirts of the broad and comparatively bare surface of 

 the ambulacrum in front of the peristome. The tubercles increase in size and distance 

 from the margin to the ambulacrum and they are placed upon Hat scrobicules, raised a 

 little at the edge here and there, with a few small granules between them in some 

 places. The boss of the tubercles is almost cylindrical and only slightly conical ; it 

 slants more or less and is usually placed not in the centre of the scrobicule. The 

 mamelon is small and tumid ; it is perforate and the collar around its union with the 

 boss is irregularly nodular, and in that sense is crenulated, but usually not all round. 

 It is evident that the anterior interradia come in contact with the peristome by means 

 of very narrow parts of the first plates, the surfaces of which are granular. The 

 lateral interradia actinally are well covered with regularly placed tubercles of the 

 same type as those of the anterior interradia ; the tubercles are closer at the ambitus, 

 whence they radiate excentrically from two or three centres, and they are also much 



