You have what is referred to as a "back-action lifter".
You can find a little information about it if you go to the main page at
www.parkerguns.org and click on the link on the left side named "Parker Grades". When the link comes up, scroll down near the bottom of the page a read the section "Dollar Grades, T-latch and Back-action". Admittedly, there isn't a great amount of information there but it should get you started.