I suggest contacting the folks at the UK Fossil Collecting Network:

https://ukfossils.co.uk/

The British Geological Survey also has descriptions of fossils from that unit:

https://www.bgs.ac.uk/mendips/fossils/fossils_jurassic.htm

but they don't list bivalves (or their casts) as being abundant.

What there is on them can be found here (scroll down):

http://www.southampton.ac.uk/~imw/liasfos.htm

It may also be part of an Ichthyosaur...

http://www.southampton.ac.uk/~imw/jpg/icve.jpg

If all else fails, try to get a non-destructive XRF test done with a portable hand-held unit. The chemistry of a fossil and fired-clay object should be quite different.

Thank you Erik, I will have a look at the fossil websites, to see if there's any possibility that its an internal cast of some sort. And I'm going to try to get hold of the stone again to have a closer look at its surface, both under a lens and a P-XRF unit.

Dave

From the second picture, I think it is not a meteorite, because the shape of the edge. I also don’t think it is a fossil. I think it is a pottery ware.   

From the second picture, we can see a hole. It is used for Firing pottery, putting a pottery ware on it to keep it separating from another.

I AGREE WITH DR. Erik 

Dear Chun Liu, yes, I agree, I had also noticed the small near-circular indentation on the concave side, and thought that this must be a tool mark, rather than a naturally-caused mark. Also, after thinking through a bit more, I believe you may be right in saying this would be fired pottery, rather than sun-baked. I would assume that sun-baked clay would have already disintegrated on exposure within humid near-surface soil for any length of time. Regards, Dave

It is a fired pottery. Firebrick also has the feature. Some Volcano burns clay have the feature, some meteorites also contain this kind of substance.

It is not today’s pottery. It is an ancient pottery ware. i have a same one, it is flat round which is called 陶珠.

D.M. Evans

Observando el ejemplar ilustrado considero que se trata de la camara de un  Nautiloideo, como lo ilustro en la siguiente imagen.

D.M. Evans

Observando el ejemplar ilustrado considero que se trata de la camara de un  Nautiloideo, como lo ilustro en la siguiente imagen.

DM Evans:

It does not give impression of being a fossil fragment. First determine mineral composition and then put a tiny fragment under the SEM to see ultrastructure for possible artefact clues.

Best

Syed

Ciao Dave, mi è capitato di campionare un giacimento fossilifero di nautiloidi (Aturia Bronn 1938) in Sicilia per conto del Museo di paleontologia dell' Università di Palermo, e di studiarne la morfologia. Il reperto che mostri nelle foto è sicuramente il setto di un nautiloide simile al genere Eutrephoceras. Nella parte concava è visibile, come descritto nella fig. allegata al messaggio di Luis Encarnación Silva, il sifone, il margine dei setti in questo genere non presenta evidenti estroflessioni. Inoltre se dovessi cercare al SEM particolari strutture, probabilmente non le troverai perché di norma si trovano di questi fossili i modelli interni in cui non permangono i microcaratteri delle struttura.

Saluti Luca.

most probably an isolated chamber of a nautiloid

Not a fossil, and probably something artefacial

Is it interesting for me to know the reasons why the find is not a fossil, or why is it an artifact? My best regard.

It has nice symmetry to it like a fossil shell would, but you say it has the texture of sandy clay, so it's not a shell.  And I agree it has a shaped and polished look to it.  And as said here, maybe the internal mold of an ammonite chamber, but I've never seen one look quite like that - they usually have certain complexities not seen here.  Do they find those simple, isolated chambers in the area? If not, it looks a lot closer to rock than fossil.

An infilling of a chamber of a nautiloid.  

Indeed this is the mould of a single nautiloid chamber.  Because the shell of nautiloids is made of aragonite, and therefore readily soluble in certain compositions of seawater as well in ground waters, nautiloid fossils often fall apart into the moulds of their individual chambers, or camerae.  Ploughing (and other sorts of erosion) readily separates them.  The smooth surface is merely the mould of the smooth septum of the original shell. 

The interesting question of how material gets inside the empty chamber in order to produce the mould would take a much longer answer!

Tim

It is a isolated chamber of a nautilid.

The isolation could be cause in destroying by weathering. Or by incomplete filling of the chambers. I show you an example from the lower lias from SW Germany.

Norbert

Thanks for all your answers, everyone. It seems most likely that it is the inner mould of a nautiloid chamber, with its central siphon tube and lack of convoluted septum. However, there is some doubt, especially over the material it is made of. I will obtain the specimen from my nephew who found it and will see what some of my colleagues at the Natural History Museum can say about its shape and its material make-up (e.g. with environmental SEM). I hope this will answer the residual questions.

David

Not a shadow of a doubt.  These are relatively common in the Middle / Upper lias junction bed in this area.  Show it to Zoe in Palaeo.

I don’t think it is an isolated chamber of a nautilid.

From the pictures, we still can see some character of isolated chamber of a nautilid before it was fossilized. It is hard shell. But the specimen before hardened is soft and flexible.

Only pottery and meteorite have had the character.

If it is pottery, we still can see the wisdom of the user. The edge shaped like this is for decreasing touch area.

I also think it is an inner mould of a nautiloid chamber. In an article "The Eocene expansion of nautilids to high latitudes" are presented several variations of this type of structure.

"The Eocene expansion of nautilids to high latitudes"

 https://www.researchgate.net/publication/263551049_The_Eocene_expansion_of_nautilids_to_high_latitudes

Article The Eocene expansion of nautilids to high latitudes

I recommend Norbert's answer

Best Regards