It appears to be a self unloading hopper/gondola car. It featured a conveyor that could unload coal or ballast. Here is a picture of one of these cars being used to load coal into the tender of one of Southern's excursion steam engines. http://www.rrpicturearchives.net/showPi ... id=1654926
The car in your photo may not be the same one in the link I posted. Yours looks like it might have a crane attachment rather than the conveyor...