davisii to Helicoprion. In 1902, Charles R. Eastman referred H. davisii to his new genus Campyloprion, but this proposal was never widely accepted. Karpinsky's identification of Edestus davisii as a species of Helicoprion would eventually be upheld by Curt Teichert, who described several more complete tooth whorls from the Wandagee Formation of Western Australia in the late 1930s. In 1907 and 1909, Oliver Perry Hay described a new genus and species of eugeneodont, Lissoprion ferrieri, from numerous fossils found in phosphate-rich Phosphoria Formation on the border between Idaho and Wyoming. He also synonymized H. davisii with his new genus and species. However, Karpinsky separated the two species once more and transferred them to Helicoprion in 1911. H. ferrieri was initially differentiated using the metrics of tooth angle and height, but Tapanila and Pruitt (2013) considered these characteristics to be intraspecifically variable. As a result, they reassigned H. ferrieri as a junior synonym of H. davisii. Outside the Phosphoria Formation, H. davisii specimens have also been found in Mexico, Texas, and Canada (Nunavut and Alberta). H. davisii is characterized by its tall and widely spaced tooth whorl, with these becoming more pronounced with age. The teeth also noticeably curve forwards.In a 1939 publication, Harry E. Wheeler described two new species of Helicoprion from California and Nevada. One of these, Helicoprion sierrensis, was described from a specimen (UNMMPC 1002) found in glacial moraine deposits in Eastern California, likely originating from the Goodhue Formation. Tapanila and Pruitt determined that the distinguishing shaft range of H. sierrensis was well within the variation found in H. davisii. H. jingmenense was described in 2007 from a nearly complete tooth whorl (YIGM V 25147) with more than four volutions across a part and counterpart slab. It was discovered during the construction of a road passing through the Lower Permian Qixia Formation of Hubei Province, China. The specimen is very similar to H. ferrieri and H. bessonowi, though it differs from the former by having teeth with a wider cutting blade, and a shorter compound root, and differs from the latter by having fewer than 39 teeth per volution. Tapanila and Pruitt argued that the specimen was partially obscured by the surrounding matrix, resulting in an underestimation of tooth height. Taking into account intraspecific variation, they synonymized it with H. davisii. H. bessonowi and synonyms Helicoprion bessonowi was first described in an 1899 monograph by Alexander Karpinsky. Although