130 THE FOSSIL ECHINOIDEA 



distance downward from the well-rounded apex the slope becomes flat, or even with a 

 slight trace of concave inbending, and then gradually curves outward with a rather bold 

 convexity or tumidity, and passes over on to the region of the slight posterior rostration 

 with a precipitous curve. The posterior margin is acute. Seen in transverse profile, 

 the sides of the test slope with a regular convex curve of great inclination. 



The actinal surface appears to have been remarkably flat, with a slight depression 

 towards the peristome. 



Apical disk very excentric anteriorly, corresponding with the summit of the test. 

 Structure wanting. 



Ambulacra broad and long, extending close to the ambitus. The right anterior 

 ambulacrum measures 14-5 millim. at its widest part, the interporiferous area being at 

 this place 6-5 millim. in breadth, and the width of the poriferous zone here is conse- 

 quently 4 millim. This great width is maintained for a considerable distance towards 

 the apex, and the diminution in breadth is slight and very gradual until close to the 

 summit. Below the point of greatest breadth the poriferous zone becomes much 

 diminished in breadth, tapering all the way to the extremity, where the pores are not 

 more than 1 millim. apart, whilst the interporiferous area is here 8"5 millim. across the 

 ambulacra, which terminate without any curve. The inner pores are transversely oval ; 

 the outer pores long and slit-like, and are united by a straight deep furrow. The inter- 

 vening costae are rather flat and tabular, ornamented with numerous very minute 

 granules, twelve to fourteen in a line, with additional small supplementary granules at 

 the outer end, which break the regularity of the line and give the appearance of a 

 small group, or even two or three lines near the junction of the costa with the neigh- 

 bouring interradial area. Sometimes the additional granules are present along the 

 whole costa, and the lineal character of the ornamentation is then obliterated ; and 

 sometimes only a few additional are present at the inner and the outer extremity of the 

 costa alike. 



The paired ambulacra are about equal in width, and the odd anterior one is a 

 shade narrower. The antero-lateral petal is bent slightly forwards from midway out- 

 wards, the character being chiefly noticeable in the outline of the interporiferous area ; 

 and the postero-lateral petals are slightly sinuous, in conformity with the undulations of 

 the posterior part of the test, the convexity, which attains its maximum about midway 

 along the petal, being directed forwards. The posterior ambulacra come well back- 

 wards, and the posterior interradium is considerably narrower than the postero-lateral 

 interradia ; towards the extremity the posterior petals in passing downwards are 

 slightly curved forwards. The ornamentation of the interporiferous area consists of 

 small, widely spaced, primary tubercles sunken in small deep scrobicules, the wide 

 intermediate spaces, which are greater than the diameter of the scrobicules, being 

 covered with very small, definite, rather widely spaced, uniform, miliary granules. 

 The ornamentation of the interradia is similar in every way excepting that in certaui 

 regions the primary tubercles are perhaps not quite so widely spaced. On the actinal 

 surface the character is changed, the scrobicules being larger and the intermediate 

 spaces narrow. 



