This is a 1920s Mabie Todd Blackbird Fountpen in black hard rubber. These pens are not uncommon and will be familiar to many. What makes this one interesting is the condition: both pen and box are pristine. Even the paper remains soft and flexible. I'll let the images speak for themselves.
https://images46.fotki.com/v147/phot...MGP0116-vi.gif
https://images43.fotki.com/v329/phot...MGP0115-vi.gif
https://images52.fotki.com/v1211/pho...MGP0117-vi.gif
https://images41.fotki.com/v1397/pho...MGP0119-vi.gif