It's a 1960s-on Stronglight crank (MARQUE DEPOSÉE, rather than the simpler, pre-60s DEPOSÉ) which looks to either have been shortened or maybe meant for a child's bike. I've never seen one like it before

This is how they are usually proportioned, with the flutes of equal length:

[IMG]Untitled by Dawes-man, on Flickr[/IMG]