How to open a Narco music box?

Anybody know how to remove the clear plastic case from an old Narco music box? A picture of it is here: [suspicious link]

I've got one attached upside down to the bottom of a ceramic figurine, and it's playing very slowly. I've seen how the governor can be adjusted to speed up a music box, and I wanted to try that, but I'm not sure how to open it up. I tried prying it lightly with a screwdriver, but it didn't budge, and I didn't want to push too hard for fear of breaking either the music box or the figurine.

Any suggestions would be appreciated.

Thanks,
Eric