332 THE FOSSIL ECHINOIDEA 



Suborder ATELOSTOMATA. 

 Family CASSIDULIBM 



Subfamily ECHINOLAMPINu^. 



Benus ECHINOLAMPAS, Gray, 1825. 



1. EcHiNOLAMPAS JTACQUEMONTr, d'ArcMac <& Haime. Plate LIII, Figs. 1-14. 



Test of moderate size. Marginal contour subovoid, well rounded in front and 

 sometimes rather flattened, the sides expanding gradually with a gentle curve up to the 

 posterior part of the lateral interradia, where the greatest breadth is situated, and the 

 margin then contracts with comparative rapidity to form a more or less distinctly rostrate 

 posterior extremity. The breadth is rather more than four fifths of the length (82-8.5 

 per cent.), the disparity being usually less in smaller examples. The apical disk, 

 which is excentric in front and corresponds with the apical summit of the test, is distant 

 from the anterior extremity a little less than two fifths of the length. The height of 

 the abactinal surface shows considerable variation, ranging from rather more than two 

 fifths to rather more than one half the length. Seen in longitudinal profile, the 

 abactinal outline presents in some forms a rather flat convexity, whilst in others there 

 is a more or less conspicuous tendency towards a conoid elevation in the region of the 

 apex, the posterior slope in either case being gentle until it takes a well-rounded, or 

 rather rapid, curve over the posterior rostration ; the anterior slope is more rapid, and 

 the margin is high and tumid. The lateral margins are thick, tumid, and well rounded 

 on to the actinal surface, which also has a tumid character in consequence of the slight 

 but distinct depression around the peristome. 



The apical disk is small, and there are four genital pores, which are of compara- 

 tively large size and occupy nearly the whole of their plate ; the anterior pair are rather 

 closer together than the posterior pair. The ocular plates are small and elongate 

 transversely, and their pores are very minute; the posterior are distinctly nearer 

 together than the anterior pair, and are separated by a more or less definite extension 

 of the central madreporic plate, which is, however, more distinctly prolonged in some 

 examples than in others. The whole of the central portion is occupied by the madre- 

 poriform body, the punctures of which are very small and numerous ; the surface is 

 often distinctly convex, and minute miliary granules are distributed irregularly over it. 



The ambulacral petals are comparatively small, and though narrow, are very 

 definitely petaloid, expanding rather rapidly for a short distance from the apex and 

 then gradually contracting, the width of the interporiferous area at the extremity being 

 little greater than half the width at the widest part of the petal, and in some instances 

 less than this. The posterior petals are the longest, and the odd anterior is the shortest ; 

 the breadth of the lateral petals is about equal (6 millim.), and the odd anterior petal 

 is slightly narrower. The breadth of one of the paired petals is in the proportion of 

 about -^Soo of the length of the test. The poriferous zones are unequal ; the anterior 



