Bruggen, A. C. van. (1980). Size clines and subspecies in the streptaxid genus Gulella Pfr. (Mollusca, Gastropoda Pulmonata) In southern Africa. Zoologische Verhandelingen. 180: 1–62.
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Bruggen, A. C. van
1980
Size clines and subspecies in the streptaxid genus <i>Gulella</i> Pfr. (Mollusca, Gastropoda Pulmonata) In southern Africa.