Arthroacantha carpenteri (Hinde 1885) ?

Is the biggest fossil at the bottom a holdfast? I have something very similiar thats mostly encased in a hunk of limestone that also has a large calyx of a Silurian Cystoid. I havent been able to identify what the other thing is though, but this fossil you have looks nearly identical to it!

I believe that it's rather the bottom of the calyx. I really am not sure about the species, though.