98 
VENTRICULITES. 
it is difficult to distinguish them correctly, without 
the assistance of an extensive suite of specimens. 
This circumstance is partly attributable to the va- 
rious stages of growth, or states of expansion and 
contraction, in which the originals were introduced 
into the mineral kingdom, and partly to the mode 
in which their remains are preserved. 
The specimens enveloped in flint, are usually of 
a cyathiform, or turbinated shape (No. 8.), while 
J’LINTS DERIVING THEIR FORMS FROM VENTRICULITES; No. S. 
xhose imbedded in chalk are more frequently 
expanded into a broad circular disk. The ex- 
ternal surface is composed of cylindrical flbres, 
that extend in a radiating manner from the centre 
or base to the outer margin, and by frequently 
subdividing and anastomosing, constitute a reticii- 
