I do not believe I have ever heard it called any thing else other than a third bite . Many makers used this method and as many of the smaller firms bought their actions from machinists such a Joseph Asbury ,the famous "JA" seen on so many gun actions and barrels it was a fairly standard feature on guns with a Scott spindle . An adaptation for guns with cam lever where the the lever had an extended finger as it would with across bolt but much heavier engaging in a slot. There was also a variation like the "hidden" third bite that employed a smaller extension with a sliding wedge also engaging in a slot in the extension this being operated by a peg connecting it to the top lever .