PLEISTOCENE FOSSILS 



127 



4. a) Shell keeled on outer margin Promenetus 



b) Shell not keeled on outer margin 5 



5. a) Shell funnel-shaped on top and bottom 6 



b) Shell funnel-shaped on bottom only Gyraulus 



6. a) Shell with internal teeth Planorbula 



b) Shell without internal teeth Helisoma 



7. a) Shell coiled to the left 8 



b) Shell coiled to the right 9 



8. a) Spire longer than aperture Aplexa 



b) Spire shorter than aperture Physa 



9. a) Edge of aperture sharp, not reflected 10 



b) Edge of aperture thick, reflected 36 



10. a) Shell longer than wide 11 



b) Shell wider than long 25 



11. a) Spire sharply pointed 12 



b) Spire bluntly pointed 17 



12. a) Aperture more than l/4 of the length 13 



b) Aperture less than l/4 of the length 16 



13. a) Aperture more than 1/2 the length 14 



b) Aperture less than 1/2 the length 15 



14. a) Whorls nearly flat-sided Lymnaea 



b) Whorls rounded Bulimnea 



15. a) Length of adult more than 3/4 inch Stagnicola 



b) Length of adult less than 3/4 inch Fossaria 



16. a) Aperture prolonged below into a short canal Pleurocera 



b) Aperture rounded below Goniobasis 



17. a) Aperture longer than spire 18 



b) Aperture shorter than spire 19 



18. a) Surface with both axial and spiral striae Pseudosuccinea 



b) Surface with axial striae only Succinea 



19. a) Aperture not reflected over umbilicus 20 



b) Aperture reflected over umbilicus 22 



20. a) Adult more than 1 inch high Campeloma 



b) Adult less than 1 inch high 21 



21. a) First two whorls coiled in same plane Cincinnatia 



b) First two whorls not coiled in same plane Amnicola 



22. a) Length and width almost equal Zoogenetes 



b) Length greater than the width 23 



