2 THE CHICAGO ACADEMY OF SCIENCES. 
margins, as in haldemani, or wide, rounded and even patulous, as in 
columella and auricularia. It varies from one-fourth to four-fifths the 
length of the entire shell. The aperture is usually angulate above and 
may be rounded, ovate or effuse below. 
The OurTer Lip (7) is always thin at the margin, but in many 
species develops a heavy varix just within the aperture, a trifling dis- 
tance from the edge. This is (apparently) notably developed only in 
those species which bury themselves in the mud during times of 
drought. These varices show on the outside of the shell as white or 
black longitudinal bands, and they vary in number from two to six or 
more. They may be observed in such species as caperata, palustris, 
elodes, reflexa, parva, etc. 
The INNER Lip (6) is reflected over the columellar region, a por- 
tion being closely appressed to the parietal wall (5) while the lower 
part may be tightly appressed to the columella, thus forming a dis- 
tinct ascending columellar plait (stagnalis, auricularia, palustris), 
tightly appressed but not forming a plait (megasoma, haldemam, colu- 
mella) or reflected and turned back, forming a broad expansion which 
overhangs the umbilicus (bulimoides, techella, caperata, emarginata). 
The Axis or PILLAR (in the upper whorls) may be gyrate or 
twisted in the form of a spiral (stagnalis), or it may form a straight 
smooth column, as in bulimoides and obrussa. All gradations occur 
between these two extremes. 
The Umpsiticus (8) may be a mere chink or narrow slit behind 
the reflected inner lip, or it may be a wide and deep hole, overhung or 
emargined by the expanded inner lip. In no case is it a hollow tube, as 
in many of the groups of fresh-water and land shells. In one species 
(Galba randolpht) a bristle may be passed to the penultimate whorl, 
but not beyond, except in abnormal specimens. In almost all individ- 
uals the umbilical opening is closed by the columellar axis of the pre- 
ceding whorl. A difference should be made between the umbilical 
‘chink, which includes those shells in which the hole is but one whorl 
deep, and the true umbilicus in which the whorls revolve around a 
hollow tube, open to the apex. The Lymnezas belong to the former 
type. 
The Nucteus or PrRoTocoNcH is a small rounded knob of from 
1% to 1% whorls, and is without distinct sculpturing. Under a glass 
the surface appears to have a satin-finish appearance. The nucleus 
varies slightly in form in many of the species (see plate XLIX). In 
a few species (umbilicata, for example) the nuclear whorls appear to 
be very faintly substriate. 
