Alonso, M.R. & Ibáñez, M. (2007)

Anatomy and function of the penial twin papillae system of the Helicinae  (Gastropoda: Helicoidea: Helicidae) and description of two new, small Hemicycla species from the laurel forest of the Canary Islands 

. Zootaxa, 1482 (1), 1–23.