80 THE FOSSIL ECHINOIDEA 



and as a whole the anterior series are more bent than the posterior. The interpori- 

 ferous zone is shallow, and not as broad as one of the poriferous zones. The postero- 

 lateral ambulacra diverge nearly as much as the antero-lateral, are much smaller than 

 the others, are slightly longer than broad, rounded, and nearly closed close to the fascicle, 

 are in shallow grooves ; and the pairs of pores are few, 8 to 11 in number. There are a 

 few minute granules on the ridges between the pairs of pores, and there is a distinct 

 longitudinal line in the interporiferous zones. Beyond the fascicle the pores of the 

 ambulacra are in single series ; and they reach the peristome, where they become more 

 numei'ous. 



The antero-lateral interradia are swollen by the keels of the odd ambulacrum, and 

 become broader anteriorly; they are very narrow near the apex, between the pores of the 

 odd ambulacrum and the anterior poriferous zones of the antero-lateral ambulacra ; 

 and this part is keeled. The postero-lateral iaterradia are also narrow at the apical 

 system, and are formed there into a long but narrow keel ; this expands rapidly 

 into the general convexity of the test beyond the limits of the ambulacra. The 

 posterior interradium is very faintly keeled between the ambulacra, and it rises 

 gradually to a point rather posterior to them ; it slopes on either side to the line of 

 the continuation of the ambulacra, and posteriorly more sharply, and is rounded off just 

 above the periproct. The plastron is long, narrow, pointed, and lowest posteriorly, is 

 generally convex from side to side, and the lip on the anterior end is slightly prolonged 

 downwards. 



The peristome is small, much the longest transversely, has a rim, and is round at 

 the sides. The periproct is elliptical and broader transversely than from above down- 

 wards ; there is a very faint flattening just below it. 



The fascicle is well developed and is peripetalous. Jt is broad, and marked with 

 many rows of granules at the end of the antero-lateral petals ; it passes thence back- 

 wards slightly, and then turns towards the apical system, running nearly parallel 

 with the antero-lateral petals for a short space; then it crosses over, not going far 

 into the angle between the petals, narrows considerably, and passes backwards and 

 inwards to reach the distal end of the posterior petals. It enlarges as it bounds 

 their end, and then crosses over the keel, narrowing and having a slight convexity 

 backwards. In front, the fascicle starts from the end of the antero-lateral petals, 

 narrows and mounts the keel on the outside of the odd ambulacrum, taking a direction 

 forwards and inwards ; still narrowing, it passes forwards, but with a less inward course, 

 and crosses the median line with a sharp curve, enlarging again there, the convexity 

 being forwards ; this part of the fascicle is slender, and is much nearer the ambitus 

 than the apical system. 



The ornamentation is remarkable for its variation in size and detail. Posteriorly 

 the ornamentation is small, and consists of very small tubercles with still smaller ones 

 between them; they are crowded, and give a granulated appearance. This orna- 

 mentation increases in size and definition on the sides towards the fore part of the 

 postero-lateral interradia ; and the tubercles are seen to be surrounded by a row of 



