
OUR COMMON FRESH-WATER SHELLS. 533 
merous teeth; while those air breathing snails, which have 
an operculum usually have a long slender tongue and have 
‘only seven teeth in a row, and in this feature they resemble 
the group now under consideration. Fig. 80 represents one 
row of teeth taken from Melantho decisa. This species con- 
tains about forty rows of teeth, and as these teeth always 
hook backward they act admirably as a rasp in licking up 
their food. The members of this family found in the United 
States represent four well marked gen- Fig, 80. 
era containing about twenty species. C 
The two principal ones are Vivipara and sl AK 
Melantho. In Vivipara the shell is gen- 
erally thinner, more globose, the ingeni teeth are always 
strongly notched; see Fig. 81. (Compare this with the 
teeth of Melantho decisa, Fig. 80). The disk of the animal 
does not project beyond the snout. See Plate 9, fig. 2. It 
will be noticed that there are two distinct folds, one on each 
side of the aperture of the shell, and these form regular con- 
duits for the water to enter and bathe the gills for respira- 
tion; the water entering by the right ~ and finding 
ig. 81. 
In Melantho the shell is 
not so globose, but is 
more solid, and the lin- 
gual teeth are smooth, 
or only slightly serrated. 
The foot also projects far beyond the snout, as in the figure 
of Melantho decisa, and the folds which conduct the water 
to the gills do not form regular tubular conduits as in 
Vivipara. We will now mention briefly the more prominent 
species, figures of which will be found in the plate. 
- Vivipara intertexta Say, Plate 9, figs. 2, 3, 4, has a very 
globose shell, yellowish green or brownish horn color, hav- 
ing numerous nearly obsolete revolving lines. The species 
3 been found in Louisiana, South Carolina and Iowa. Vi- 
