There are a couple of options for mounting:
- It comes with rubber feet on the bottom, and can just sit on top of a lid, provided there's some sort hole for the food to fall through
- You can pull out the rubber feet, and use the (provided) clamps to clamp it to the side of the tank (or other vertical surface). Again, you need a hole in the top of your tank for the food to fall through.
- There's a definite 'up/down' orientation; the food falls through the bottom of the feeder into the aquarium.
The feeder's lid doesn't lock in place, so I don't see a way to mount it to the top/inside of an aquarium lid, though you can probably put the feeder on some sort of shelf or bracket inside the tank.