I am sure that you can get better information, but since no one else
touched it, I will try.  First, it is probably Paleozoic.  The
Pleurotomariaceans (slit shells) were often dominant in  gastropod
faunas.  But that means there are many genera to choose from, although
the long slit is not too common.  Secondly you need to make a cast of the
natural mold that you exposed.  If the surface is well preserved, and not
too obscured by the crystals inside or by recrystalization of the
surrounding aragonite mud to calcite (limestone) outside, you can have a
nice representation of the shell in rubber.  (Probably the easiest way is
to convince your dentist to mix up some of the material he makes
impressions with and squeeze it carefully into the molds to minimize air
bubbles.)  Then you can start with the Treatise volume on Gastropods and
work from there.  You may also want to bring the rock to a local college
with a geology program as they may be familiar with the formation it came
from, which can greatly help narrow down your search.  Good luck!


On Fri, 4 Dec 2009 12:30:31 +1100 Bob Dayle <[log in to unmask]> writes:
> For any interested:
>
> I picked up a rock a couple of days ago while walking on an
> abandoned railroad
> grade. It had a different color and more 'texture' than a lot of the
> grey-blue
> ancient sea bottom variety, of which I have cracked many.
>
> This one weighs about a kilogram. It fractured into four pieces on
> the second
> 'tap' with a six-pound (~2.4 kilogram) sledge hammer. I found a
> geode inside,
> just as I had hoped; however, the shape was hardly expected.
>
> I have posted a page with photos. (Pardon the lack of image quality.
> I just
> received this USB microscope and I am still getting the hang of
> using it.)
>
> The page is at:
>
> http://cowry.org/research/snailcast.htm
>
> If anyone is a fossil geek and has an idea as to the type of snail
> shell that
> caused it, please drop me a line.
>
> Bob Dayle
> webmaster - http://cowry.org
>
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