4 6 
sented Plate IV. Fig. 21, with one of the spines lying close to the 
papilla on which it had been fixed. In this specimen may be seen the 
characters of the echinus. This, it is evident, is a species of Cidaris 
papillata ; but differing from any which has been described, in having 
the articulations of the assulae much more concealed by the granular 
surface, which is extended from papilla to papilla. In another spe- 
cimen, Plate IV. Fig. 1, in chalk, four of the spines are still adherent ; 
and in another, in which several spines and two of the larger areas 
are imbedded in chalk, the particular character of this shell is also 
plainly manifested. In another flint specimen from Pangbourn, in 
Berkshire, the spine is somewhat different, the longitudinal grooves 
being deeper, and the denticulae more distinct. 
The origin, therefore, of the Lapides Judaici or petrified olives, as 
these stones were formerly considered, is therefore now determined ; 
and the species of echinite also, to which they belong, is completely 
ascertained. 
I am indebted to that accurate observer of nature, Mr. Sowerby, for 
a very ingenious suggestion, as to the cause of a peculiar variety of 
figure which sometimes occurs in these spines. They are sometimes seen 
more than usually tumid and irregularly rugose : this he imputes, and I 
am assured of his being right, to the spine having suffered from disease. 
The second species, Cucumerince, is divisible into several varieties, 
in which, although the cucumber form is preserved, very considerable 
differences are observable. In some, the surface is neither striated 
nor granulated ; but irregularly and slightly nodular. But the surface 
in general possessed by these bodies, is formed by small granular or 
denticulated projections, disposed in regular rows. Plate IV. Fig. 2, 
6 , 8, 15 , 16 , and 17- 
Plate IV. Fig. 15, is one of the cucumerine species of the largest 
size ; and at Plate IV. Fig. 2, is one of the larger area; of one of the 
mammillated echinites, with a narrower spine of this species attached 
to it. These bodies, whose origin was so long a subject of such vague 
