OF NORTH AMERICA. 199 



The writer has followed the suggestion made by Meek in 1876, 

 that this group should be raised to full generic rank. The strong axial 

 ribs, which are equidistant, are very distinctive. It is not particularly 

 related to Acella, although the shape of the shell has led several authors 

 to place it in close relationship with the slender Acella haldemani. The 

 nuclear and first post-nuclear whorls of haldemani are very different, 

 as is also the general shape of the body whorl. 



The only species of the genus (which is extinct) is described in 

 the chapter on fossil Lymnseas, page 91. 



Genus GALBA Schrank, 1803. 



Galba SCHRANK, Fauna Boica, III, pt. 2, pp. 262, 285. Sole example Bucci- 

 num truncatulum Miiller (vide Dall). 



SHELL: Turreted or elongated, whorls gradually increasing in 

 size, the last whorl generally of moderate size; spire usually long and 

 pointed ; outer lip typically not expanded, usually a thick rib being de- 

 veloped just within the edge in the adult; 1 axis not gyrate, forming 

 an almost straight pillar from spire to umbilicus; the columella is 

 strongly plicate in one group but entirely smooth typically; axis with 

 perforation or imperf orate; the inner lip frequently forms a heavy 

 spreading callus. 



ANIMAL: Not differing essentially externally from the other 

 Lymnaeas. 



JAW : Superior jaw wide and low, arched, with a median swell- 

 ing on the ventral surface. Lateral jaws very long. 



RADULA : Lateral teeth bi-or tricuspid. 



GENITALIA: Penis always shorter than penis-sac; prostate long- 

 ovate or elongate-pyriform, very large, its duct generally short. 



DISTRIBUTION : Holarctic and Palearctic. 



A close study of the groups Galba and Stagnicola has convinced 

 the writer that they both represent the same type of Lymnaa. The 

 pillar is nearly straight in both groups (the difference of the axis not 

 being of generic value) and old individuals of both groups form a vari- 

 cal thickening within the outer lip. 2 The genitalia are also of the same 

 type. The characters mentioned are quite different from those of any 

 of the preceding groups and at once differentiate this type of Lym- 

 naeid from Lymncea, Radix, Acella and Bulimnea. 



The genus naturally splits into three (possibly four) groups, 

 Galba sensu stricto, with usually a smooth shell, a non-plicate colum- 



'Stagnicola. In Galba and Simpsonia it is not usually developed to so 

 great a degree. 



2 This has been seen in obrussa, parva and modicella and may be observed 

 in some individuals of any large series. 



