pupa's impression and possible cast?

[hndmarshall]

[hndmarshall]

more on this stone......more weird things...

 

[hndmarshall]

did a puddy cast of the piece of something in the pupa which turns out to be a fossilized part of the pupa here is an impression of the bugs upper portion

 

[Kane]

Not sure a pupa would fossilize in this type of rock.  

[hndmarshall]

4 minutes ago, Kane said:

Not sure a pupa would fossilize in this type of rock.  

but it is there....or its impression and upper part is...

[JohnJ]

@hndmarshall it truly is not a pupa.  It is a piece of silicified rudist reef.  The pupa looking parts are the internal sections of the rudist. Other bits of broken rudists and shells are also present.  When found as chert nodules, like yours, the details preserved can be amazing.  However, your specimen has also been through millennia in the "gravel grinder". 

 

Rudists of the Fredericksburg Group are beautifully weird.  Found as partials or in cross section, they can look like many other things.

Partial rudists that look like fish ribs.