Evans/Welty hump filler

The closest relative to the ubiquitous crescent filler is the Evan’s hump filler. The rotating collar is nearly identical, but it fits into a notch at the edge of the hump.  The design was initially used on the Welty WAWCO branded pen, and later on the Evan’s branded pen, based in Waterloo, Iowa. The Evan’s imprinted pens appear more often than WAWCO, and their production is likely from the mid to later 1910s.  These seem to be exclusively in black hard rubber, and were marketed as lower end, more affordable pens.