Text copied from TM9-1885-2 German Explosive Ordnance 1953 :

Description: The mine consists of a wooden box which contains a ½pound demolition block fitted with a ZZ42 igniter and detonator. The box is covered by a hinged lid.

Operation: Pressure on the box lid pushes the pin out of the igniter, freeing the striker and causes detonation of the igniter cap, detonator and explosive charge.

Remarks: A modified Schümine with a special large lid and sloping front, designed to employ the ZZ35 igniter, was also encountered. The sloping front engages on an actuating pin pushed through the normal wire hole in the top of the igniter. The modified mine has a hole in the lid so that a cord can be tied to the safety pin and the igniter armed from a safe distance.

The photos below © Pat.
They show 3 different schü-mines. I have another variation in my own collection, made from normal wood ánd plywood.

Made from normal wood. 

Made from plywood.  

Made from pressed board.