314 THE CHICAGO ACADEMY OF SCIENCES. 
mud, the author cannot state positively, but his opinion is that it marks 
periods of hibernation and has nothing to do with the annual growth 
of the shell. The presence of this varix is not, however, a sign of 
maturity as has been stated, for it may be found in a shell of three 
whorls. One specimen from Halma, Minnesota, has four varices 
placed close together on the body whorl. 
Fully adult palustris has seven full whorls; the majority of speci- 
mens, however, have from four to six whorls. Individuals of four 
whorls are frequently seen with the aperture and spire about equal, 
which appear at first sight distinct from palustris. In some speci- 
mens the body-whorl is flattened and a heavy varix is formed. These 
shells are two-thirds grown having formed the varix preceding the 
formation of the last body-whorl. A form of palustris occurs in Lake 
George, Florissant, Colorado (pl. XX XIII, figs. 14-18) which is re- 
markably flattened from front to back, and the inner lip in the mature 
shell is reflected in such a manner as to form a broad, smooth projec- 
tion which emargins the umbilicus, leaving a conspicuous chink. The 
spire and aperture are about equal in length. These shells were er- 
oneously identified by the writer as swmassi Baird. Some of the speci- 
mens in this lot are heavily malleated. The genitalia and radula do 
not differ from those of palustris. 
The surface of many of the large, fragile forms, as at Alpena 
and in Owasco Lake, is strongly malleated. These shells may be taken 
as typical palustris. The shells of palustris vary considerably in their 
thickness, some being as thin as paper while others are quite thick 
and solid. The columellar plait also varies markedly in prominence in 
different individuals. Specimens from California (pl. X XXIII, fig. 
24) are frequently very wide and corpulent, the body whorl being al- 
most globose. Such a form is shown by Binney in his fig. 61. Several 
specimens have been seen which have the first five whorls jet black 
while the last two are rich horn-colored, the line of demarcation be- 
tween the two being very strong. A collection from Deuel County, 
South Dakota, contains a number of individuals which are heavily 
striped in zebra fashion. A single reversed specimen has been col- 
lected by Dr. William A. Nason, at Stony Point, near Alpena, Michi- 
gan. It consists of four whorls and measures 9.50 mill. in length. 
No attempt has been made to correlate the European varieties of 
palustris with those of America. They have been developed along 
parallel lines, but cannot be said to be identical, though resembling 
each other very closely. The varieties corvus, turricula, decollata 
(Jeff.), roseolabiata, fusca and many others have their counterpart in 
