25 
The toTp-like madrepore (madrepom turbinata), Plate IV. Fig. 1, 2, 3, 
&c. smo6th, with a concave hemispheric star, is a zoophyte, only known 
in a mineralized state. 
This species of madrepore has in general a conical figure, the lower 
part of the cone being often very much contracted, as if to form a 
pedicle. From this point, the body of the fossil gradually enlarges, 
until it terminates in a truncated apex ; or is previously prolonged into 
a cylindrical oblong body. In either case, the surface is divided by 
numerous, small, and hardly perceptible longitudinal striae, and girt with 
transverse, obtuse, and unequal furrows. 
The star which fills the apex is concave, and formed by sulcated, 
or lamellated, and frequently even, dentated rays, proceeding from 
the central depression to the edge of the cavity, which is generally 
acute. 
These fossils are commonly formed of a lime-stone, which, in general, 
is internally of a light, or yellowish brown colour ; but they are mostly 
externally of a bluish grey, deriving this colour from the matrix in which 
they have been imbedded. 
These madreporites vary much in size ; some hardly exceeding that of 
a horse-bean ; whilst others are three or four inches in length, and others 
of even nearly that diameter. 
No investigation respecting these fossil substances has been conducted 
with so much success as that which has been instituted by the learned 
author of the Dissertation on the Baltic Corals. Nor can the figures 
with which he illustrates the several varieties of this species of madre- 
porite be exceeded, in exactness of representation. To atone, therefore, 
to those who have it not in their power to refer to those figures, for 
their repetition here, I have, as I have in every other parallel case, 
endeavoured to select such specimens for the engraver, as may serve also 
to point out some important circumstance to which the figures in former 
works do not refer. 
VOL. II. 
E 
