Thanks for the informative piece below.  Wish we had some living around
here to play with.  The closest geographically is the high mountains of
Hispaniola, which I think remains undescribed.  Anyway, I (and others, I'm
sure) appreciate the illumination.

Here's another one.  Have you ever seen that helicarionid from San Tome
Island (I think) which has a false operculum?  The upper part of the
apertural lip is hinged with periostracum and when the snail retracts, it
flops down over the aperture.  It's pretty cool.  I can't remember the
genus.....

Kurt

At 08:43 AM 7/12/99 -0400, you wrote:
>Kurt,
>
>The best (and only) explanation of the structure & function of the clausilium
>of the Clausiliidae that I could find is in Kerney & Cameron's "A Field Guide
>to the Land Snails of Britain & North-West Europe". This is what they say:
>"...the upper attenuated end of [the clausilium] is fixed to the columella.
>When the animal is crawling the clausilium is pushed elastically out of the
>way into the groove between the columellar & subcolumellar lamellae, but on
>retraction [of the snail] the expanded end springs out against the palate &
>blocks entry into the shell." You really need to break open a shell to fully
>understand how this happens. I examined one of my broken Albinaria shells. If
>I had had a digital camera I would have taken pictures for all to see. I
>suppose the clausilium originated as a columellar tooth. It starts from the
>columella about a whole turn behind the aperture as a stiff but flexible
>ribbon, spirals around the columella then expands into the clausilium proper.
>When I gently pushed on the clausilium with a needle coming from the
inside of
>the shell (just as the snail would have done), it moved towards the dorsal
>side of the shell, opening the entrance. Note that the clausilium always
>remains inside the shell.
>
>Hope this helps.
>
>A.