Polygonal patterns produced by thrashing of tadpoles in silty sediments were observed by S. W. Maher (1962) in small ponds near Wartburg, Tenn.; the author has observed identical structures, with associated tadpoles, in small brooks on the island of Crete. Morphologic criteria are given for distinguishing tadpole polygons from interference ripple marks of inorganic origin. E. Hitchcock (1858) first described supposed tadpole marks from Triassic siltstone of Massachusetts, under the name Batrachoides. Later authors considered these to be interference ripple marks. Moreover, the name is preoccupied by Batrachoides Lacepede 1800, a fish. Benjaminichnus is here proposed to replace Batrachoides Hitchcock 1858 for recent tadpole structures and for any fossil biogenic structures with the same characteristics.