The family Enidae is characterized by mostly tall shells with or without apertural teeth. Among the Turkish enids there are some genera with superficially similar shells.
For example, the shell of Borlumastus yildirimi, below (left),
looks quite like that of Imparietula leucodon, below (left).
Although I. leucodon tends to be slightly larger, the resemblance is striking.
However, their genitalia tell a different story. Imparietula leucodon has an appendix (a), which B. yildirimi lacks. Furthermore, in B. yildirimi bursa copulatrix (bc) has a diverticulum (d) and the epiphallus (e) has a flagellum (f), while both of which are absent in I. leucodon.
It appears that although the genitalia diverged during evolution, the overall shell morphology was maintained. Either that or the shell morphologies were initially different, but subsequently converged to similar morphologies.
1. The shell and genitalia pictures of B. yildirimi are from: Örstan, A. & Yıldırım, M.Z. 2004. Borlumastus, a new land snail genus from Turkey (Gastropoda: Pulmonata: Enidae). Basteria, 68:125-129. pdf
2. The shell picture of I. leucodon is from: Bank, R.A. & Neubert, E. 1998.
Notes on Buliminidae, 5. Systematic position of Arabian Buliminidae (Gastropoda Pulmonata) with the description of a new genus. Basteria 61:73-84;
the genitalia picture is from: Hesse, P. 1933. Zur Anatomie und Systematik der Familie Enidae. Archiv für Naturgeschichte NF 2:145-224.
3. Other abbreviations: p, penis; v, vagina; c, caecum; vd, vas deferans; go, genital opening; rp, retractor of penis; fo, free oviduct.