The Memory Snake is an unused item in Mother 3 (Earthbound 2), in which is assumed to be similar to the Ruler in Mother and Earthbound. The Memory Snake is not a key item(unlike the Rope Snake, as it is more of a joke item than anything else). The Memory Snake is blue in colour, and seems longer than the Rope Snake. It is also very straight, like a ruler.
The Memory Snake might be related to the Rope Snake in some way, since they are both similar looking.