You are missing the RACK which counts the hours. The rack interacts with the snail as shown in your one picture. The rack HOOK appears in this same picture. But you may also be missing other parts. Can' t tell. I have uploaded a couple pictures of one of these Howards which I hope will help.
The the image on the left, above, shows the snail (shown in your picture), and the bottom end of the rack where it contacts the snail, just prior to the strike starting. A/ is the indexing pin, B/ is the rack, and C/ is the snail.
The right image shows the top end of the rack with the triangular teeth, the rack hook (preventing the rack from dropping), and the gathering pallet which lifts the rack one tooth with each half revolution. I don't have a picture of the complete rack. A/ is the gathering pallet, B/ is the top end of the rack, and C/ is the rack hook.
