of a Fossil Alcyonium. . 405 
DESCRIPTION OF THE PLATES. 
Tas. XXVII. 
Fig. 1. Alcyonium Chonoides, partly expanded. 
a. The tubuli arising from the outer, and terminating 
on the inner surface. 
b. Foramina through which the radicle fibres passed. 
The muscular coat is not seen in this specimen ; 
the siliceous matter which fills up its funnel-like 
cavity having enveloped the external surface.—A 
fragment of an Echinus is attached to the stirp, near 
the base. 
2, 3. Flints deriving their forms from the inferior part of the 
stirp: vide Tab. XXVIII. Fig. 2. 
4. Resembles figure 1. The cavity is nearly filled with 
silex; some of the tubular openings are visible on 
the internal surface. i 
5. Horizontal section of a flint, showing the thickness 
of the integuments near the base. 
Tas. XXVIII, 
These rare and interesting specimens beautifully illustrate 
the origin of the siliceous fossils delineated in the preceding 
plate. TONES rg ioja Las] 
Fig. 1. A mass of chalk, bearing on its superior surface the im- 
pression of the fibrous integument of Alcyonium Chonoides. In 
the centre is imbedded a flint of a funnel-shape, its margin and 
base possessing an appearance similar to those of the fossils before 
mentioned. The same description applies to Fig. 2, with. this 
exception, that the upper part of the flint: is less expanded than 
in Fig. 1., and assumes more of a cyathiform figure. The diffe- 
362 rence 
