Mayer & Grammelspacher Eureka rubber dart guns
Mayer & Grammelspacher 'Eureka' dart guns
No, they are not air pistols - rather they use a spring to launch rubber sucker-tipped darts, but because 'Eureka' brand guns were made by Mayer & Grammelspacher (Diana), they are part of the story...
This ad courtesy of Trev:
The 1911 Alfa catalogue had 'crossed dart pistols' to illustrate the brand and the M&G logo at the time included crossed rubber-tipped darts:
With thanks to Mick W for these pics, which show a Eureka gun, but one with 'Paris' markings (?):