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 

 T i(ras™\m'\w«SCT(\&\m\M!H spightly impressed. 



J. ^TOwSfflv^^fflw The body whorl takes 



up almost the entire 

 length of the shell. 

 FIG. .43. mrithasho^aid^n. Enlarged. yj^^ incurvcd aperture 



and the operculum are "crescent-shaped, the body of a dusky grey color, 

 the tentacles long an'd 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 

 lyi 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, 

 algae and confervse 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 



impressed suture. The 

 body whorl is marked 

 by three well-defined 

 reddish-brown bands 

 which diminishtowards 

 the smaller whorls. 

 The thick snout and 



FIG. 144. Potomac Snail, Fi-viparus Timiparus. lon£ CUTVCd 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, is found in canals, lakes and slow streams, 

 sometimes in ponds and ditches. The shell is brownish-green in color 



