Gastropod or something similar?

[cameronsfossilcollection]

Hey again, this is a very tiny ~.5cm shell that I found some time ago at the regular road cut at the Lost River exposure of the Mahantango Formation. I would guess it’s a Gastropod or something similar but if it could be narrowed down any further I would be elated. Thanks guys!

[Rockwood]

The shape does seem asymmetric enough to be a gastropod, and the growth ridges would seem right. I'm not sure it's complete enough to rule out the idea that the straight edge is a hinge though. 

[Ludwigia]

It could also be from a brachiopod.