Deep blue sea shell

1st post! I bought this glass scallop shell at a thrift shop the other day because its blue colour is so deep and intense. It has peculiar marks on the base end which may be a hallmark, maybe a grip, or perhaps it’s simply part of the design. I’ve searched and can’t find anything like it on the web so I’m wondering if anyone here has seen such a thing?
Cheers!

Hello, I believe those marks are just design details. It was likely an insert for inside a metal shell dish - if you search on a site like Etsy, for "cobalt blue glass shell dish silver butter dish" it should come up :)

Thanks RooBarb, I'm confident that's it! I'm sure my search parameters where way off base.
Thanks again!