LYMNZID© 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 
tc place it in close relationshgp 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 Lymnzas, page 91. 
Genus GALBA Schrank, 1803. 
Galba SCHRANK, Fauna Boica, III, pt. 2, pp. 262, 285. Sole example Bucci- 
num truncatulum Muller (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;' 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 imperforate; the inner lip frequently forms a heavy 
spreading callus. 
AnIMAL: Not differing essentially externally from the other 
Lymnzas. 
JAw: Superior jaw wide and low, arched, with a median swell- 
ing on the ventral surface. Lateral jaws very long. 
RaApuLA: Lateral teeth bi-or tricuspid. 
GENITALIA: Penis always shorter than penis-sac; prostate long- 
ovate or elongate-pyriform, very large, its duct generally short. 
DistrisuTion: Holarctic and Palearctic. 
A close study of the groups Galba and Stagnicola has convinced 
the writer that they both represent the same type of Lymn@a. The 
pillar is nearly straight in both groups (the difference of the axis not 
heing of generic value) and old individuals of both groups form a vari- 
cal thickening within the outer lip.*_ 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- 
xeid from Lymnea, 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- 
14Stagnicola. In Galba and Simpsonia it is not usually developed to so 
great a degree. 
E “This has been seen in obrussa, parva and modicella and may be observed 
in some individuals of any large series, 
