26 
The corallite represented at Plate IV, Fig. 2, differs, in its figure, 
from the other corallites of this species ; having somewhat of a discoid 
appearance. This difference, I suspect, has depended entirely on the 
age of the coral: the labours of the little modeller not having been 
here so advanced as in those which have the turbinated shape. In this 
specimen, the diameter of the disk more than equals the height of the 
coral : the depth of the stellated cavity is therefore necessarily small. 
The rays pass from the centre of the cavity, and terminate in the 
margin ; which appears to be preternaturally thick, from its edge 
having probably been somewhat worn down, by rolling on the shores 
of the Baltic, whence it was obtained. From the same circumstance, 
perhaps, has proceeded the flatness of the stellated surface ; the pro- 
jecting parts of the radiating lamellae having been also worn down. 
Sufficient, however, remains, not only to convey a correct idea of the 
structure of the fossil, but to shew that it was a dwelling exactly fitted 
for the accommodation of the animal described by Donati, as the 
inhabitant of madrepores. 
By a careful inspection of many of these madreporites, I have 
learnt, that they have been attached to the substance on which they 
have grown, by tubes bearing the form, and so far performing to them 
the office of roots, as to secure them from easy removal from their 
native spot. This pedicle I consider as an essential part of these 
animal substances ; and I trust, I shall be able to establish its exist- 
ence sufficiently often, to warrant the assumption of its having existed 
in all those bodies in which it cannot be directly manifested, but in 
which its admission will render their nature much less difficult to 
understand. 
On the reverse, or inferior side of this fossil, longitudinal striee, 
answering to the internal radiating laminae, may be easily traced ; and 
are intersected by distinct transverse ridges and grooves, marking the 
progressive increase of the madrepore by the successive labours of its 
