
MOLLUSCS, VERMES AND HYDROZOA 

and of a greenish-yellow horn color. The three whorls are convex, the 
spire very much de- 
pressed and the suture 
spightly impressed. 
The body whorl takes 
up almost the entire 
length of the shell. 
The incurved aperture 
and the operculum are crescent-shaped, the body of a dusky grey color, 

FIG. 143. Neritina showalderi. Enlarged. 
the tentacles long and the eyes prominent. 
The Neritina are widely distributed in Europe and tropical countries 
but only these two are native to the United States. 
Viviparus. These snails inhabit marshy places, still water, rivers 
and streams. They have the whorl of the shell very convex, an angulated 
aperture and a horny operculum showing concentric lines of growth. The 
larger species of the Eastern and Middle States attain a length of shell of 
114 inches. The females of most of the genera have evenly developed, 
sharply pointed tentacles, while the males have the right thicker and more 
bluntly pointed. These snails live exclusively on dead animal matter, 
alge and conferve and are harmless to aquarium plants, though not as 
active as the Planorbes. They were formerly classed as the Paludina. 
V. Viviparus, Fig. 144, the most common species, inhabits ponds and 
still water. It has a thick, well-rounded oblong olive-green or brownish 
shell of four or five inflated, sharply defined whorls; a brunt apex and deeply 
Ate impressed suture. The 
+ ab body whorl is marked 
by three well-defined 
reddish-brown bands 
which diminish towards 
the smaller whorls. 
The thick snout and 
FIG. 144. Potomac Snail, Viviparus viviparus. long, curved, flexible 
tentacles and the body are bluish-grey with faint orange and yellow spots. 
The projecting eyes are placed upon short pedicels under the tentacles, 
and the foot is bluntly ovate and broad. The operculum is ovate and 
shows concentric rings. This snail is ovoviviparous, the eggs hatching at 
different periods in the oviduct, at which time the snail secretes itself in 
the mud or pebbles. It is common to America and Europe, and is popu- 
larly known as the “Potomac snail.’’ Abundant at Washington, D.C. 
V. georgianus, Fig. 145, 1s found in canals, lakes and slow streams, 
sometimes in ponds and ditches. The shell is brownish-green in color 

222 
