Join Date: Jun 2011
Location: Sunnyvale, California
Bikes: Bridgestone RB-1, 600, T700, MB-6 w/ Dirt Drops, MB-Zip, Bianchi Limited, Nashbar Hounder
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The second set of pics would have been more helpful to begin with. The two saddles are NOT compatible with each other. One has flat rails (right thumbnail) and the other has standard round rails (left). Most saddles these days use the style on the left. You have a different clamp and saddle on the right. Your seat posts are also different. The one on the right uses a collared clamp to secure saddle to seat post. The one on the left uses a single bolt integrated clamp.
There is the possibility that you can measure the seat post diameter of both bikes and if they are the same, then you can swap the whole seat AND seatpost. Otherwise, you'll need to get a new saddle clamp for round rails and check the top diameter of the clamp so it conforms to your bare seatpost.