18 THE FOSSIL ECHINOIDEA 



Peripetalous fascicle complete, more or less indented between the lateral ambu- 

 lacra. Lateral fascicle branching off from the peripetalous fascicle near the extremity 

 of the antero-lateral petals, and passing below the periproct with a rapid curve. 



Tubercles small, prominent ; scrobicules very shallow. 



1. LiNTHiA SiNDBNSis, sp. nov. Plate IV. 



The test is rather depressed; marginal contour roundly heart-shaped, truncate 

 behind, and broadly and rather deeply grooved in front. It is as broad as it is long, 

 the greatest breadth being in a line with the apical system, and the margin being 

 more rounded in front of this line than behind it. The upper surface is more or less 

 uniformly convex, and the posterior interambulacrum slightly carinated. Seen in 

 longitudinal profile, the highest point of the test is situated opposite the middle of 

 the posterior ambulacra, the posterior declivity being sharply truncate behind and 

 sloping at a high angle to the margin, whilst the anterior is gradual and well rounded. 

 The transverse profile is almost semicircular, the posterior keel being slightly prominent. 

 The under surface is rather inflated ; the margins tumid, except posteriorly, where the 

 test is rather deeply impressed. It is well rounded in the neighbourhood of the 

 postero-lateral ambulacra. 



The apical system is slightly excentric in front. There are four large generative 

 pores ; and a small madreporiform body is connected with the right anterior plate. 

 The posterior pair are much wider apart than the anterior pair ; and those of each 

 side are very close. This arrangement pushes the ocular plates of the antero-lateral 

 ambulacra to the outside of the generative plates. The anterior ocular plate, how- 

 ever, comes well between the front generative plates, and separates them completely, 

 whilst the madreporiform body, which is rather large, separates the posterior ocular 

 plates. The ocular foramina are very small. 



The ambulacra are unequal, rather broad, and moderately sunken. The anterior 

 pair are much longer than the posterior, in the proportion of 2 : 3j and are also more 

 divergent. The odd anterior ambulacrum is feebly developed, wide, and not very 

 deeply sunken until near the margin. The pores are minute and round ; the first five 

 or six pairs are very small and are placed in close succession near to the apical system. 

 Further out the plates become broader and the pores wider apart and oblique, and 

 there is a raised partitipn which separates one pore from another. The antero-lateral 

 ambulacra are long, straight, ovate lanceolate, petaloid, broadest at the outer third, very 

 wide apart, and enclose an angle of about 126°. In length they occupy fully two thirds 

 of the distance between the apical disk and the margin, and are rather deeply sunken. 



The poriferous zones are broad where fully developed, the pores being conjugate 

 and elongate, except near the apex, where they are circular ; about 27 pairs exist in 

 each poriferous zone, the outer pairs being close to the peripetalous fasciole, but not 

 touching it. The interporiferous area is very narrow, scarcely more than half the breadth 

 of a poriferous zone. 



The postero-lateral ambulacra are narrower, and shorter by one third than the 

 anterior pair, and are much less divergent, the angle enclosed being 66°. They are 



