ECHINITES. 211 



as in many other echinites, with minute circles inclosing papillae . 

 These markings are made too conspicuous and too regular, in Dr. 

 Plot's figure, Tab. II. Fig. 11. 



No. 9 of our Plate, is of the same class, but from the alluvium. 

 It bears a considerable resemblance to No. 2; but is of a more 

 oblong form, and has its largest petals towards the point of the heart,^ 

 and the smallest in the sulcus, or furrow, at the top. The two petals- 

 next to that, also reach the margin ; and the two largest approach to 

 it. The vent in this specimen is very conspicuous. 



The last echinite which we would notice particularly, is re- 

 presented in Figure 4, A and B. Though it is one of the most 

 common in our oolite, at Brompton, Silphoue, Malton, and other 

 places, we have not found it described by any author. It perhaps 

 ought to form a fourth class of the echinite family ; for its vent is- 

 neither in the vertex nor in the base, neither on the side nor near 

 the margin of the upper surface; but is situate at the upper end of a 

 deep sulcus, which runs from the margin to very near the vertex. 

 The vent is, therefore, near the vertex ; yet it does not open vertically, 

 but laterally, having its aperture towards the deep groove, and the shell 

 between that and the vertex forming an arch or roof over it ; so 

 that it resembles a cave opening into a deep ravine. The shell is 

 nearly cordate, and contrary to what we generally find, the vent is 

 towards the broader end, the deep sulcus forming the depression at 

 the top of the heart. 



The upper surface ( A ) displays a flower with five petals, each 

 of which contains two double rows of pores ; and the pores in each 

 double row are connected by delicate cross lines, as in No. 2 and 

 No. 5. The petals do not end abruptly on the disk, but all extend 

 to the margin; from whence, as in No. 5, the pairs of biporous am- 

 bulacra are continued along the base, the whole terminating in the 

 mouth; as may be seen in Figure B. The base of the shell, especially 



