40 THE TERTIARY FOSSIL ECHINOIDEA 



crowded until the anterior fascicle is reached. On the flanks of the keels the 

 tubercles are crowded, and are larger on the inner than on the outer side. 



The lateral interradia have a keel near the apical system and some gibbosities 

 further out ; and the ornamentation is of small tubercles, which become larger towards 

 the margin, but which never equal the medium-sized tubercles of the anterior inter- 

 radium except close to the ambulacrum at the margin. 



The posterior interradium has a very decided, narrow, elevated keel on it in the 

 median line, the upper surface of which is nearly horizontal in front and curved 

 gently behind. The tubercles of the interradium are very small near the apical 

 system and far back, and only become slightly larger and less crowded on either side 

 and below the periproct. 



The peristome is small, far in front, and is semilunar in shape. The upper lip is a 

 smooth narrow plane which slants from the ordinary level of the test upwards and 

 inwards, and is marked by the oblong slits of the peristomial ambulacral pores. The 

 lower lip is at the end of the plastron, is ridged at its free curved edge, and projects 

 slightly downwards ; it is decidedly lower than the upper part of the peristome. The 

 plastron is irregularly elliptical in outline, is very slightly convex, and terminates 

 posteriorly in a projection; the tubercles on it are close, and are on flat, slightly 

 elevated scrobicules, which are longer than broad, and which radiate in lines from the 

 projection forwards and outwards, the largest tubercles being those in front. The 

 bosses are nearer the front than the back part of each scrobicule. 



Actinally the ambulacra are slightly grooved and very plain as regards their 

 ornamentation. Slit-like pores are seen ; and the posterior ambulacra limit the 

 plastron laterally. 



The fascicles are two in number, the peripetalous and the latero-subanal. 



The peripetalous fasciole bounds the end of the petaloid antero-lateral ambulacrum, 

 and is continued inwards close to the poriferous zone as far as the inner one fourth of 

 the ambulacrum, and therefore close to the interradial ridge; it then passes back- 

 wards and slightly inwards to the posterior ambulacrum, the greater pait of the outer 

 poriferous zone of which is environed by it. The fasciole limits the end of the ambu- 

 lacrum and passes over the keel in a curved direction, concavity backwards, to reach 

 the opposite ambulacrum. In front of the end of the antero-lateral ambulacrum the 

 fasciole turns inwards and forwards, and reaches the top of one of the crests of the 

 anterior ambulacrum ; it passes over the crest in a long slant forwards, inwards, and 

 downwards to form a V-shaped curve on the groove, the concavity being backwards, 

 and then it joins the fasciole of the opposite side. 



The lateral fasciole starts from a small gibbosity about halfway between the 

 outer and inner ends of the posterior poriferous zone of the antero-lateral ambulacrum, 

 passes as a thin line with a backward, downward, and very slightly outward trend, and 

 then downwards, backwards, and inwards to curve beneath the periproct about halfway 

 between it and the projection of the plastron. 



The fascicles are composed of exceedingly minute granules very closely packed, 



