VENTRICULITES. 
99 
kited integument ca})able of very considerable con- 
traction and expansion. 
The fibres are solid, and when viewed through 
a lens exhibit a porous structure, bearing consider- 
able resemblance to dried sponge. The meshes, 
or interstices between the fibres, are narrow and 
elongated in the specimens that are expanded, but 
very irregular in those which are corrugated by 
contraction. In some instances, slender transverse 
filaments extend from one fibre to another, by 
which the entire plexus is more firmly connected 
together. The surface of the interior, or funnel- 
shaped cavity, is studded with- small perforated 
tubercles, or papillae, the open extremities of short, 
straight, cylindrical tubes, that arise between the 
fibres of the external integument, and passing in a 
transverse direction, terminate on the inner surface. 
Siliceous casts of these tubuli are frequently observ- 
able in flints deriving their form from ventriculites. 
The base forms an elongated stem or stirps, and 
terminates in diverging root-like processes, by 
which the original was fixed to other bodies. 
This zoophyte, when contracted into a cylin- 
drical form, is from one to six inches in length ; 
when expanded, its diameter occasionally exceeds 
nine inches : the thickness of its substance is sel- 
dom more than 0*2 inch. 
The siliceous specimens exhibit no traces of 
organization, except at the margin and base ; the 
outer surface of the original being obscured by the 
silex, in which it is imbedded. In some ex- 
amples, however, the enclosed zoophyte may be 
separated from the surrounding flint by a well 
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