Dorsetensia is a narrowly coiled discoidal ammonite from the early Middle Jurassic, lower Bajocian, belonging to the family Sonniniidae of the superfamily Hildoceratoidea. The inner whorls are ribbed or smooth, outer whorl is smooth. The outer rim (venter) is narrow, with a keel running along the middle. The umbilicus, the opening in the middle of the shell exposing inner whorls, is of moderate size with a sharp, sometimes undercut edge.