ZB-47 Sub Machine Gun

The ZG47 was a postwar Czech development of the submachine. It's main thrust was to eliminate the protruding magazines that made other designs awkward to handle.  The magazine laid flat under the weapon, the shells pointed upwards and were fed through a wheel into the chamber. The wheel was turned by a rod attached to the bolt. The result was an odd mechanism that was expensive and required precision machining to work reliably.
 To hold the firearm, the right thumb was inserted in the larger hole with the trigger being in the smaller one. 

More here.

Manual with many illustrations here.