The first material known from the genus were the prominent fin spines that curve anteriorly over the head of the animal. When first described in 1883 from the St. Louis Limestone, these remains were given the name Physonemus falcatus.
The first recorded examples of this genus featured prominent dorsal fins that curved towards the front of the animal's skull, a notable feature also observed in other related species. These remains were first identified in 1883 from the St. Louis Limestone and were subsequently named Physonemus falcatus.