Upgrading a theme to 1.8-What happened to pageshells?

I had overriden the default view in a 1.7 plugin, with a custom pageshell.php. Now I've decided to move development to 1.8, but now no pageshells. What's the equivalent in 1.8?

I'm sure it's documented somewhere, but I couldn't find it.

Thanks for any tips,

Chris