Kociolek, J.P. and Stoermer, E.F. (1988) Taxonomy, ultrastructure and distribution of Gomphoneis herculeana, G. eriense and closely related species (Naviculales: Gomphonemataceae) Proc. Acad. Nat. Sci. Phil. 140: 24-97 http://www.jstor.org/stable/4064935