Maxwell-Huygens, Newton-Cartan, and Saunders-Knox Spacetimes

I address a question recently raised by Simon Saunders [Phil. Sci. 80(2): 22-48 (2013)] concerning the relationship between the spacetime structure of Newton-Cartan theory and that of what I will call "Maxwell-Huygens spacetime". This discussion will also clarify a connection between Saunders' work and a recent paper by Eleanor Knox [Brit. J. Phil. Sci. 65(4): 863-880 (2014)].