Thanks, David, and to everyone else who helped answer my questions. It's interesting to learn a little more about the planet's transformation and how it influenced the different life forms.
The fossil is in such nice condition I really wanted to identify it. It sure resembles Gryphaea arcuata more than it does other species of Gryphaea. I wanted to learn why/how our little Utah shell seemed to be the same species as one from such (now) distant places as 
 England, Germany, or France. 


---- David Campbell <[log in to unmask]> wrote: 

=============
North America actually started splitting from Europe and Africa in the late
Triassic (hence the Triassic to early Jurassic basins along eastern North
America, which have some fossil freshwater clams in them).  However, as
continents move about as fast as your fingernails grow, the Atlantic was
still pretty narrow in the mid-Jurassic, or even Cretaceous, and there was
some land connection off and on through Greenland between Europe and North
America until much later.  So the Jurassic early north Atlantic was
certainly narrow enough to allow planktonic larvae to get across.  There
are several species of Gryphaea, so a bit of research would be needed to
check definitely which species are possibilities.

In the Jurassic, some ocean connections west or southwest to the Pacific
were present from time to time bringing the ocean to what is now the
montane West.  The often Gulf of Mexico to Arctic interior seaway was
primarily a Cretaceous feature.  However, the Gulf of Mexico was opening,
too, and Central America was well in the future, so the species could have
traveled along the south coast of North America all the way to the
Pacific.  Incidentally, seawater that was trapped in the early rift valleys
as the Gulf of Mexico opened evaporated to make the salt deposits noted in
another thread.


On Fri, Jan 8, 2016 at 5:10 PM, Batt, Richard <[log in to unmask]>
wrote:

> G. arcuata is very common in Texas (the so-called "Devil's Toenails") and
> further north, and there are  other species from parts of the Cretaceous
> there and in the Western Interior.
> Since North America and Europe were still connected until much later in
> the Cretaceous, and the shallow Western Interior Seaway would have been
> continuous through Texas and across the Mississippi Embayment aulacogen
> feature, across Florida and up the east US coast onto GreAt Britain and
> Europe ( still at the time all part of the same continent) it would make
> sense that species such as this could have had a continuous distribution.
> When I was doing amonite work I came across some shallow-water nektobenthic
> ammonite species found in both Colorado and Europe, and the shallow
> nektobenthic ammonites did not undergo any post-mortem transport.
>
> Sent from my iPad
>
> > On Jan 8, 2016, at 4:56 PM, "[log in to unmask]" <[log in to unmask]>
> wrote:
> >
> > I notice that Grypaea arcuata has been found in Britain and Europe.
> Would our Gryphaea necessarily be the same species? Were the seas and/or
> landmasses so connected during or just prior to the Jurassic that the one
> found in Utah could be from a group that became isolated as the land masses
> rose, dividing the seas?
> >
> >
> > ---- Allen Aigen <[log in to unmask]>
> wrote:
> >
> > =============
> > Gryphaea is marine.
> > Allen
> >
> >      From: "[log in to unmask]" <[log in to unmask]>
> > To: [log in to unmask]
> > Sent: Friday, January 8, 2016 10:52 AM
> > Subject: Re: [CONCH-L] Fossil snail with operculum-link to photos
> >
> > Perhaps they are related. Was G. arcuata a terrestrial, fresh water, or
> marine critter?
> >
> > ---- John Wolff <[log in to unmask]> wrote:
> >
> > =============
> > They look like Gryphaea arcuata (Lamarck, 1801) I have from England's
> > Lower Sinemurian, Jurassic (200-150Ma).  I believe they are called
> > "Devils' toenails"
> >
> > John
> >
> > At 08:33 PM 1/07/16, you wrote:
> >> ASU has just received this lovely fossil snail from Fred Skillman,
> >> an amateur entomologist who found it in a wash on private land near
> >> Delicate Arch, Arches National Park, Utah. It is such a treasure for
> >> me because it actually has what appears to be fossilized animal and
> >> an operculum which became separated when he was cleaning off
> >> caked-on dirt. I just had to share with all of you. We think it may
> >> date back to the Jurassic.
> >>
> >> To see 5 photos just copy and paste the following link onto your
> >> search engine.
> >>
> >>
> https://drive.google.com/drive/folders/0B-Vz8pRKgeC8M1NLa1k4U2VZNDg=============
> >>
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-- 
Dr. David Campbell
Assistant Professor, Geology
Department of Natural Sciences
Box 7270
Gardner-Webb University
Boiling Springs NC 28017

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