120 THE NAUTILUS. 



(I) The first lateral tooth of the radula has three cusps, the 

 others two. 



The epiphallus longer than the penis. Color pat- 

 tern of the mantle conspicuous. Adult with a 

 flaring lip (Subgenus Radix) L. auricularia p. 179 



(II) The lateral teeth of the radula with two cusps. 



(1). 1st cusp grooved : epiphallus less than penis. (Subgenus 

 Acella) L. haldemani. . . . .p. 192 

 (2). 1st cusp ungrooved. 



(A) Axis gyrate : epiphallus J of penis (Subgenus 

 Lymnaa} Stagnalis Group. . . .p. 136 



(B) Axis not gyrate. Epiphallus equal or less than the 

 penis but over . (Subgenus Gaiba). 



(a) with not evident spiral sculpture 



Galba Group . .... p. 200 



(b) with evident spiral sculpture, 

 (aa) Ratio between two and three 



Palustris Group . . . . .p. 298 

 Ratio between 1^ and two. 



(aaa) Ovate shell, narrow inner lip, no true 



umbilicus Catascopium Group . . p. 377 

 (bbb) Bulbous shell, wide inner lip and umbil- 



cus Emarginata Group . . .p. 408 



(III) Lateral teeth with three cusps. 



(1) Axis gyrate. 



(A) Epiphallus less than the penis ; shell succiniform 

 Subgenus Pseudosuccinea Columella Group . p. 162 



(B) Epiphallus less than the penis. 



(a) Shell thin and transparent color pattern of 

 mantle visible through shell lip flaring in 

 adult ratio less than 1|. (Subgenus Radix) 



L. auricularia . . . . p. 179 



(b) Shell solid bulimiform ratio greater than 

 1^. (Subgenus Bulimnea). 



L. megasoma . . . . .p. 183 



(2) Axis not gyrate (Subgenus Pseudogalba). 



Epiphallus usually shorter than the penis. 



(aa) Inner lip flattened out and excavated. 



L. umbilicata . . . . .p. 236 



(bb) Inner lip erect. L. parva . . .p. 243 

 (b) Epiphallus usually longer than the penis, 

 (aa) 10 mm. long, has 5 whorls 



L. humilis. . . . . . p. 25 



(bb) 10 mm. long, has 4 whorls 



L. obrussa. . . . . .p. 270 



