I spotted this in the gravel in the front garden of my Mother's neighbour in Romsey, Hampshire. I have no idea where the gravel originated.
Looking at other postings here and images on the InterWeb, I'm pretty certain this is a Cretaceous sponge fossil, but I'd be grateful for authoritative confirmation.
If so, is it possible to identify the species?
Yes, it is a sponge, but it is difficult to ID as far as species.
The gravel is quite likely to be derived from the chalk (quite possibly via erosion, redeposition and quarrying), hence a Cretaceous age is very likely. And sponges are one of the most common fossils of the flints in the chalk. From its age and spherical shape, I would guess it might be Porosphaera, of which some species are mentioned here - http://www.cretaceous.de/Porosphaera.html
They come up for ID/discusion on NaturePlus now and them, eg.
Thanks for your quick reply.
Is the smooth 'cap' on the top and bottom of the fossil likely to have been part of the original sponge's structure, a later deposit/accretion, or perhaps due to erosion? Most of the examples of Porosphaera I've looked at (since you replied) don't appear to have that feature. There is a distinct edge to it, easily felt with the fingernail.
I also have a couple of sea urchin fossils, dug from the clay in my Dorset back garden when excavating the footings for a largish shed, which were identified by the Dorset County Museum some years ago.