xiv The Molluscan Family Planorhidae 



IV. Distribution in Time and Space 37 



A. Geological History and Distribution 37 



B. Geographical Distribution 38 



Dispersal of Species 39 



V. Historical Sketch of Classifications 41 



VI. A New Classification of the Family Planorbidae . 45 



General Discussion 45 



Anatomical Keys to Groups 46 



Systematic List of Genera and Subgenera Recognized in 



This Work 48 



VII. Systematic Account of the Subfamilies, Genera, and 



Subgenera — Recent and Fossil 50 



Subfamily Planorbinae H. A. Pilsbry, 1934 50 



Genus Planorbis Geoff roy, 1767 51 



Genus Anisus Studer, 1820 (Gray, 1847) 55 



Subgenus Anisus SS 57 



Subgenus Costorbis Lindholm, 1926 61 



Subgenus Bathyomphalus (Ag.) Charp., 1837 .... 62 



Genus Odontogyrorbis Lorenthey, 1906 64 



Genus Gyraulus (Ag.) Charp., 1837 65 



Subgenus Gyraulus SS 66 



Subgenus Torquis- Dall, 1905 72 



Genus Armiger Hartmann, 1840 75 



Genus Taphius H. and A. Adams, 1855 79 



Genus Tropicorbis Pilsbry and Brown, 1914 80 



Subgenus Tropicorbis SS 85 



Subgenus Obstructio Haas, 1939 85 



Subgenus Lateorbis F. C. Baker, New Subgenus ... 85 



Genus Afroplanorbis Thiele, 1931 86 



Genus Syrioplanorbis F. C. Baker, new name for 



Heterodiscus West 88 



Genus Biomphalaria Preston, 1910 89 



Genus Australorbis Pilsbry, 1934 90 



Genus Anisopsis Sandberger, 1875 94 



Subfamily Segmentininae F. C. Baker, New Subfamily ... 96 



Genus Segmentina Fleming, 1817 96 



Genus Hippeutis (Ag.) Charp., 1837 100 



Genus Polypylis Pilsbry, 1906 104 



Genus Helicorbis Benson, 1855 106 



Genus Trochorbis Benson, 1855 108 



