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Family Physida 
G9. Genus Physa 
19. Shell-large, sinistral with aperture occupying 
two-thirds the length of the shell. Fine 
growth lines, revolving lines faint or absent. .P. gyrina 
g. Shell small, not over 5 mm. in length, umbilicus small 
Family Amnicolidce 
G10. Genus Amnicola 
20. Shell low conic, apex rounded, four to five 
whorls A. limosa 
21. Shell inflated, more globose, more widely 
umbilicated than above A. porata 
22. Shell narrow and high, five to six whorls. . .A. lustrica 
h. Shell small, not over 6 mm. in width, widely umbilicated 
Family Valvatida 
Gil. Genus Vahata 
23. Shell thin, with rounded whorls without 
carinse V. sincero 
• 24. Shell thin, whorls usually bearing three 
carinse, on base, periphery, and shoulder of 
whorl, but occasionally one or more may 
be absent V. tricarinata 
