The first version has a bar attached to the "thumb piece" that extends along the bottom of the action for a couple inches.

https://www.bonhams.com/auctions/19797/lot/114/


The second version lacks this extension.

https://www.bonhams.com/auctions/22750/lot/81/?category=list


“I left long before daylight, alone but not lonely.”~Gordon Macquarrie