Size clines and subspecies in the Streptaxid Genus Gulella PFR. (Mollusca, Gastropoda pulmonata) in Southern Africa

CONTENTS 1. Introduction.................. 3 2. Systematic part................. 6 Gulella adamsiana................. 7 Gulella darglensis................. 14 Gulella elliptica................. 19 Gulella farquhari................. 27 Gulella infrendens................ 33 Gulella planti...................................... 39 Gulella vicina....... ....... 44 Gulella zuluensis................. 49 3. Concluding remarks................ 54 4. Summary................... 58 5. References.................. 58 6. Index to trivial names in Gulella............. 62 1. INTRODUCTION The concept of subspecies has been applied to terrestrial molluscs at a comparatively early stage. Mayr (1942) quotes the works of Rossmässler (1826), Kobelt (1881), the Sarasin brothers (1899), Gulick (1905), and particularly Rensch (since 1929) as examples of proponents or precursors of this concept. Since the 1930s the polytypic species has been generally accepted among students of land snails. However, so far it has played a relatively minor role in comprehensive works on African (Afrotropical) land molluscs, such as Pilsbry (1919), Connolly (1939) and Bequaert (1950) 1). Undoubtedly a fragmented topography (e.g., island areas such as Indonesia)