Fascinated as I am by detail, I think it would be fun to try to illustrate as many "Scroll" / "Celery" / "Ribbed Shell" feet, handles and general prunts as we can find. Close up images and info on the number of ribs and whether there are extensions or apendages to, or as part of, the main ribbed shell deisgn would all be needed.
If we could do this we may start to come up with a decent reference collection that might also be able to be tied in with known registered designs.
In Mervyn Gulliver's Victorian Decorative Glass, British Designs 1850-194, there is a starter showing some registered designs of "Ribbed Shell" feet etc. for the various Richardsons dynasty, Thomas Webb & Sons and Boulton & Mills.
As for Barbara's dish, I certainly think the decoration is on the "fancy" side which suggests American to me - maybe it is Northwood, but I wouldn't know. What is interesting, though, is that the Ribbed Shell feet have those extra bits of fancy, waved-scroll sections rising up the side of the bowl. Are those extensions integral with the feet or overlaid?
I think Leni's vase is English (Stourbridge, for want of a more precise attribution). The "odd" thing to me is that the feet are really nice but the rigaree and the "Continental" style of flat, sliced-off rim seem to be slightly out of keeping. As a pure guess, I'd suggest Boulton & Mills.