jg THE TEBTIAEY FOSSIL ECHINOIDEA 



elliptical in outline, elongate nearly vertieally, and is partly visible from the acUnal 

 «nvfarp but not from the abactinal. , , . . , i „ 



me apical system is situated in front of a broad keel in the odd mterambulacmm, 

 a.db?JnTatt'surface which lead, in front to the narrow shallow groove for fte 

 Tntrior ambulacrum; it is small. There are four generaUve pores, of wta h he 

 poLor pair are the largest and widest apart; the antenor pa>r are close to the 

 p«Sor; and the madreporio body extends between the posterior patr and postenorly 

 to them being larger than the area included by the pores. 



XreoId'anteL ambulacrum in the groove has a brdad floor ; and the pores, 

 elongate, very visible, and few in number, are on the slope of the broad keel-hke 

 eminences which bound the groove. The pairs of pores are wxder apart anteriorly. 



The anterior pair of ambulacra are long, nearly transverse m direction, and are 

 placed in wide and deep grooves, which become flush with the general surface at the 

 outer end of the poriferous zones, not far from the margin. The grooves are broader 

 and deeper than that which includes the odd ambulacrum: they dimmish m 

 breadth externally, and the anterior edge is slightly convex to the front, the posterior 

 being straight. The interporiferous area is narrow and finely granular, and is on the 

 base of the groove ; and the poriferous zones are broad and partly on the flanks of it. 

 The pores within the groove are very large, nearly circular in outline, those of each 

 pair being separated by a na,rrow process and conjugate, and there are about twelve 

 pairs in each zone. But nearer the apical system, at the commencement of the groove, 

 there are, in each zone, a pair of small pores and four pairs of almost microscopic ones, 

 ending close to a minute ocular pore, The poriferous zones do not curve together at 

 the outer extremity of the groove, and the petal is not closed ; the peripetalous fasciole 

 is in close contact with this part of the ambulacrum. 



The posterior pair of ambulacra are the longest, are in deep grooves, which are 

 narrower than those of the antero-lateral pair ; they diverge at a very acute angle and 

 are close together, being separated by the narrow, convex, keeled interambulacrum, 

 whose extreme breadth is not more than twice that of the grooves. These ambulacra 

 are nearly straight ; but towards their ends they curve slightly forwards, become flush 

 with the test, and are bounded by the fasciole. The petals do not close. There are 

 about eleven or twelve pairs of large pores within the groove, and the interporiferous 

 area is narrow. Nearer the apex there are a few very small pores. 



The anterior interradials are roundly keeled at the anterior groove, tumid else- 

 where, and pass into the rounded margin. The ornamentation on top of the flat keel 

 on either side of the anterior groove, just in front of the apex, is of close rows of flat 

 tubercles in sets of four, and they become irregular and smaller towards the front and 

 also near the antero-lateral ambulacra. On the slope of each interradium in front are 

 tliree irregularly placed groups of large tubercles sunken in deep scrobicules and 

 adherent to one side of them. The first group is a solitary tubercle, which may be 

 flanked by two smaller ones ; the second, inferior to the first and separated by the 

 fasciole, is a long irregular linear series of six tubercles; and the third, still nearer 



