A laterally activated lever is seen on BB Stylo pens, and is also said used on Held pens. The little dent holds the lever in place. Swing it to the side and compress the sac. I have not been able to find a patent for the lever. The patent date shown relates to the stylo ink delivery on the BB Stylo pen.
David Nishimura has an in depth blog post about BB Styo and Held. Vintage Pen News: Held and B.B. Stylo
