Operculum oval; outer opercular markings concentric rings; shell not 

 tuberculate 54. 



54. With the outer opercular markings concentric, the central ones spiral; 



whorls usually faintly keeled; about V2''; Ohio southwards 

 Lioplax subcarinata (Say) Keeled Mud Snail 

 Opercular markings concentric; whorls usually smooth 55. 



55. Spire very much shorter than the aperture; shell with revolving bands 



of color; about 2"; Georgia and Florida 



Pomacea paludosa (Say) Infusoria Snail 

 (Ampullaria depressa Say) 

 Spire about as high as the aperture; color banded or plain; smaller; 

 eastern and central states 56. 



56. Operculum limy; color greenish'yellow; about Y2" 



Bythinia tentaculata (Linn.) 

 (Buhmus tentaculatus (Linn.) ) 

 Operculum horny; getting to be larger 57. 



57. Upper part of aperture forming an angle of about seventy degrees; shell 



usually dark or with revolving bands of color - — • Dark or Banded Mud 



Snails 58. 



Upper part of aperture forming an angle of about fifty degrees; shell 



usually plain greenish — Green Mud Snails 60. 



58. Spire slightly shorter than the aperture; umbilicus present, except in 



southern forms; Mississippi drainage 



Vnnparus intertextus (Say) Brown Mud Snail 

 Spire usually longer than the aperture; umbilicus absent or a very narrow 

 chink 59. 



59. With four dark bands; N. Y. to Michigan 



Vwiparus contectoides Binney Banded Mud Snail 

 (Paludina vwipara (Say) ) 

 Without bands; Mississippi drainage 



Vivipariis suhpurpureus (Say) Purple Mud Snail 



60. Shell rather thin; upper whorls usually eroded; northeastern and north- 



central states 



Caynpeloma decisum (Say) 

 Shell solid to heavy 61. 



6L Whorls usually rounded; aperture usually about as long as the spire; 



apical whorl sunk within the second whorl 62. 



Whorls usually somewhat flattened; aperture often shorter than the 



spire; apical whorl raised above the second whorl 63. 



62. Shell usually reddish beneath the epidermis; east-central and central 



states 



Campeloma rufuiyi (Haldeman) 

 Shell white beneath the epidermis; shell very thick and heav>'; N. Y. to 

 Texas 



Campeloma ponderosum (Say) 



63. With six whorls; upper Mississippi River 



Campeloma integrum (Say) 



120 



