Littorina saxatilis

Rob Durrant These found under a stone on an exposed beach in a small mid-shore pool, where were abundant Littorina saxatilis and Gibbula umbilicalis. Shares qualities of both, and presumably Gibbula of some sort. What, please?

Simon Taylor I'd say these are young Gibbula umbilicalis

Dave Rolfe I would agree. Assuming it is mainland Britain, if it were the channel Islands I may say G.pennanti.

Rob Durrant Thanks, Simon. To me, the raised lines on the shell surface and the patterning being speckled more than lines differentiated these from all the other G. umbilicalis around, but it was mainland, Dave.

Ian Smith If you look at the G. umbilicalis account at http://www.flickr.com/photos/56388191@N08/9871482474/in/set-72157635756387204 and scroll down to "similar species" and click on the links, you will see why these are young Phorcus lineatus.

Jan Light I agree with Ian's ident. The genus name that might be more familiar to some is Osilinus or even Monodonta.

Rob Durrant Certainly the Monodonta tooth is very clear on one of the images, which I did notice; but am not sufficiently knowledgeable about whether other species might share that characteristic.

Rob Durrant I will reread your very thorough study on Flickr, Ian Smith, just had a glance at the relevant section. Again, thanks for that resource. Eventually I will learn! But I am somewhat encouraged when it isn't always obvious even to those far more expert than me :D

Ian Smith Identifying 3D curved objects from 2D images is much more difficult than with object in hand. "he who never made a mistake never made a discovery" (Samuel Smiles).

Julia Nunn I think they are Littorina saxatilis and Gibbula umbilicalis. They don't look like any juvenile Phorcus/Osilinus/Monodonta I have ever seen.

Julia Nunn I agree that one of the pics looks very like G. pennant - I was about to ask the same question about the area they were found

Simon Taylor I am happy to concur that these are juvenile Phorcus. I wasn't 100% happy with the ribs. Presumably there were adults at the site too.

Rob Durrant I can't say I was aware of any, Simon. Not to say there weren't; but I was very conscious of large numbers of G. umbilicalis. It was a beach of strata running perpendicular to the prevailing waves and even barnacle cover was not great; so I was concentrating on the few crevices and undersides of the few stones that I could manage to lift. Pretty low down the shore, at least lowest part of mid-shore. Don't you think that the tooth is the most telling feature, given that juveniles of both species, as Ian's extensive collection of images shows, can present very similar appearances?

Dave Rolfe I have to confess I did not notice the tooth, but having done so and also having read others views I also have to agree that it does look like juvenile P. lineatus.