What is "stegomastodon"

Stegomastodon ('roof breast tooth') is an extinct genus of gomphothere, a family of proboscideans. It is not to be confused with the genus Mammut from a different proboscidean family, whose members are commonly called "mastodons", nor with the genus Stegodon, from yet another proboscidean subfamily, whose members are commonly called "stegodonts".