42. Columella folded or twisted; surface of shell with a malleated appear' 



ance; about 1" 



Lymnaea (Stagmcola) palustns (Mi.iller) Hammered Pond Snail 



Columella smooth; shell with lengthwise growth lines and often with 



fine spiral lines; about ^2'" 43. 



43. Inner edge of aperture slightly curved over the umbilical area 



Lymnaea (Galha) humilis Say 

 (Includes Lymnaea modicella Say) 

 Inner edge of aperture turned in a more or less triangular expansion over 

 the umbilical area 44. 



44. Shell solid; epidermis standing erect on the spiral lines 



Lymnaea (Galha) caperata Say 

 Shell thin; spiral lines impressed 



Lymnaea (Galha) ohrnssa Say 



45. Inner edge of operculum with small projections which fit into depres' 



sions in the base of the columella; fresh and brackish waters of the 

 Florida and Gulf coasts 



J\[eritina reclivata (Say) Wavy-lined Shell 

 Columellar area of aperture not serrate 46. 



46. Shell cup' or turban-shaped, with three whorls, very thin and trans- 



parent; inner side of aperture very broad; Alabama 

 Lepyrium showalteri (Lea) Turban Shell 

 Not so 47. 



47. Aperture circular; operculum circular, with multispiral (tightly wound) 



markings; body whorl slightly disjoined; usually less than %" 48. 



Aperture approaching oval; opercular markings concentric or slightly 



spiral; body whorl not disjoined 52. 



48. Shell much higher than wide; Atlantic states 



Lyogyrus pupoideus (Gould) 

 Shell about as wide as, or wider than, high 49. 



49. Whorls rounded 50. 

 Whorls keeled 51. 



50. Operculum with about ten spirals 



Valvata sincera Say Smooth Valve Shell 

 Operculum with about four spirals 

 Horatia micra (P. ^ F.) 



5 1 . Apex somewhat elevated 



Valvata tncannata (Say) Three-keeled Valve Shell 

 Apex low 



Valvata hicarinata Lea Two-keeled Valve Shell 



52. Opercular markings concentric (outer markings concentric, central 



markings spiral, in one species) 53. 



Opercular markings spiral 64. 



53. Inner margin of operculum reflected, making the opercular markings 



concentric half rings; shell heavy and usually with tubercles; Alabama 

 Tulotoma magnifica (Conrad) Knobby Shell 



119 



