Art,
Shell shape is sometimes deceptive, as there are few basic forms that
have been independently evolved many times.  Trying to guess what is
descended from what is subjective, but you seem to be prejudiced against
extinction of large groups.  It happens...
Allen Aigen  [log in to unmask]

On Wed, 15 Nov 2000 22:41:58 -0500 Art Weil <[log in to unmask]> writes:
> Dear Joe;-
>     I understand the dieing out of Hormatoma----but did it do so
> without
> branches, descendants, etc.? It appears nothing like  a
> "Slit-Shell", but very
> much like slim coiled families----Terebra, Epitoniidae, Miters, etc.
>         Art
>
> Joe and Nora wrote:
>
> > Hello Art,
> >
> > Joe here. I sifted through my collection and literature. All of
> our
> > 'Hormotoma' specimens are Ordovician or Silurian in age. This is
> mostly a
> > North American fossil (although also found 'rarely' in Europe). It
> was
> > usually placed (despite its outward appearance) until the 1940's
> in the
> > superfamily Pleurotomariacea by some authors. Its kin, Mourlonia,
> somewhat
> > resembles descendents through to the Pleurotmaria.
> > Subsequesnt authors do not place it in this superfamily but place
> it  in
> > agroup archaeogastropods with no further lineage. It is thought to
> die out
> > in the Silurian. It is thought by most to have no relationship
> with the
> > modern pleurotomaria.
> > Most authors ( some exceptions) do not accept any known
> antecedents of the
> > modern Pleurotomaria until the Mesozoic age.
> > Your species 'gracilis' was first placed in the genus  Murchisonia
> (Hall,
> > 1847) and subsequently changed by the author to Hormotoma sometime
> in the
> > 1850's (I 'think').
> >     Nora and I just obtained a scanner and it is surprising how
> well it
> > scans small fossils. Sometime in the not too distant furue we'll
> scan some
> > paleozoic gastropods, mesozoic pleurotomaria, etc. and make them
> accessible
> > to Conch-L subscribers to view.
> >
> > Original Message -----
> > From: "Art Weil" <[log in to unmask]>
> > To: <[log in to unmask]>
> > Sent: Tuesday, November 14, 2000 7:34 PM
> > Subject: Hormotoma
> >
> > > Dear (probably Old Seashells and Andy);-
> > >         What I have here is a Hormotoma gracilis (maybe
> Homotoma?). It
> > > measures 13.48mm long and is about 400 million years old. Since
> a
> > > fleeting glance makes it look like an Epitonium (or Cerith or
> other
> > > coiled critter) I wondered if there is some descendency from the
> fossil
> > > that I have. Inquiring minds want to know.
> > >             Art