Motion is a significant feature of the visual world that animals depend on to survive, either by capturing prey or escaping predators. Retinal ganglion cells (RGCs) are neurons that are responsible for processing complex features of the visual scene and transmitting that information to the brain as electrical signals called spike trains. Two pieces of visual information are needed to determine the motion of an object: its position and speed. Out of the 40 identified types of RGCs in the mouse retina, the ON alpha and PixON RGCs are most likely to encode motion, as they are abundant in the region of the retina that looks forward at prey items. In this study, we recorded the responses of ON alphas and PixONs to a motion stimulus—moving bars of light projected at 5 different speeds over the retina—to determine whether a significant difference between their responses could explain their contribution to motion encoding in the mouse retina. Cell-attached recordings of spike trains triggered by the moving bar stimulus, as well as voltage-clamp recordings of inhibitory and excitatory inputs to the RGCs, supported the notion that there was a fundamental difference between the ON alpha and PixON responses to speed. The firing rate of ON alpha cells tended to increase as the speed of the bar increased, while the firing rate of the PixON fired at a similar rate in response to all speeds. Our result suggests that the brain may combine positional information from the PixON with speed information from the ON alpha to build a complete picture of motion. Understanding how the retina encodes motion is an important step forward in identifying the circuit mechanisms of the retina to build retinal prosthetics that can restore vision lost from the destruction of RGCs.