Hi, my name is Ellen. I work here on reception
at the Lapworth Museum and my Object of the
Month is the Portland Screw.
Now, you know, we all go on campus for a coffee
and I'm always fascinated by the shapes that
the bakers come up with for their cakes that
are on sale. For example, the cinnamon swirl
always reminds me of the curly snail. And
one of my favourites is the cream horn and
we just got obviously a pastry case here but
it shows you the shape of the Portland Screw.
We have one here which is a modern day snail
shell but it gives you an idea of the shape
that was created. Now what's fascinating about
these is how they create the spiral. The mollusc
inside would have secreted more aragonite
on one side than the other, and therefore
create the equiangular spiral of the shell.
And, as it grew, then shell grew with it.
These over time obviously sank to the sea
bed and the acid waters and the carbonite
muds replaced the shell itself. And that's
what's fascinating about this particular rock
sample we have here is that actually it leaves
a cast, an echo of the shell inside, and you
can see here, and here those forms.
What was unique about the Portland screw,
and why it gets its name, is that it had an
extra ridge around the edge of the shell which
allows it to burrow into or screw into the
sand in the shoreline which gave it an advantage
over its other gastropod relatives as it was
more difficult for a scavenger just to get
it out of the sand. [Music]
