260 THE CHICAGO ACADEMY OF SCIENCES. 
A recent study of numerous species of this genus has 
convinced the writer that some classification other than the 
one in use must be found. The present grouping by shell 
characters is totally unsatisfactory on account of the extreme 
variability of the individuals. For example, different forms 
of L. emarginata Say var. mighelsi Binney, recently examined, 
can be placed in all of the so-called ‘subgenera usually recog- 
nized (Radix, Bulimnea, Limnophysa, etc.), and in fact the typ- 
ical emarginata is typical of Limnophysa, and the variety 
mighelst of Radix; all of the intermediate forms occur and 
absolutely connect the extremes. In view of this fact the 
writer has discarded all subgenera, using simply the generic 
term Limnza. Some divisions of value will undoubtedly be 
found when all of the species are examined anatomically for 
the genitalia, radula, etc. There is abundant work in this line 
for a naturalist having the time and material at his command. 
104. Limnza columella Say, pl. xxx, fig. 26. 
Limnea columella Say. Journ. Phil. Acad., Vol. I, p. 14, 1817. 
Limnea navicula V ALENCIENNES, Rec'd. Obs., Vol. II, p. 251, 1833. 
Limnea chalybea GOULD, Am, Journ. Sci., ed. 1, Vol. XXXVIII, p. 196, 
1840. (Variety.) 
Limnea acuminata ADAMS, 1. c., Vol. XXXIX, p. 374, 1840. 
Limnea strigosa LEA, Proc. Amer. Phil. Soc., Vol. IJ, p. 33, 1841. 
Limnea coarctata LEA, |. c¢., p. 83, 1841. 
Limnea casta LEA, |. c., p. 33, 1841. (Variety.) 
Succinea pellucida LEA, Proc. Phil. Acad., p. 109, 1864. 
Limnea columellaris ADAMS, Amer. Journ. Sci., ser. 1, Vol. XXXVI, 
p. 392, absq. descr. 
Limnea succiniformis ADAMS, MS., teste Haldeman. 
Shell: Ovate, somewhat pointed, thin, fragile, transpar- 
ent; color light greenish or yellowish horn; surface shining, 
covered with rather coarse growth lines, and encircled by im- 
pressed spiral lines; whorls four, rounded, rapidly enlarging, 
the last one three times the size of the rest of the shell; spires 
sharply conic, rather short; apex small, very dark brown; su- 
tures impressed; aperture ovate, dilated, expanded at the lower 
part; the aperture varies from long and narrow to wide and 
somewhat expanded; peristome thin, acute; columella narrow, 
twisted; terminations of peristome connected by a thin callus; 
umbilicus generally closed but sometimes very narrowly per- 
forate where the callus is not fully developed; the columella 
is so narrow that a view may be taken from the base nearly to 
the apex, as in Succinea retusa. 
7 ees rie ts 
. - . 
