Here's an Eclipse bag I had a few years ago displayed on my old Mondia using an uncommon attachment system. The black clamp on the seatpost is called an SPT = Seat Post Thing, also by Eclipse. Nice to have another option - basically acts as an oversized seat pack.
At one point in the not-so-distant-past I had 3/4 of these bags. Today I'm down to one near-NOS one in blue.
DD