IX MOLLUSCA 115 



Limnaea palustris [the Bog Snail) (see Fig. 65). — This is a 

 smaller species, with shell ^ to 1 inch long. Whorls 6 or 7, 

 and narrower than in stagnalis; shell browner and thicker, 

 mouth narrower. Eather too fond of delicate plant food to 

 be a desirable inhabitant of a tank ; also apt to escape from 

 the tank unless covered ; 60 to 80 eggs are laid in a roughly 

 cylindrical capsule. 



Limnaea peregra {the Wandering Snail). — Shell f inch long ; 

 5 whorls. Body whorl, and also the mouth of shell, very 

 large ; outer lip a little reflected ; very common. Feeds on 

 decomposing animal matter as well as on vegetation; apt 

 to leave the water, migrating to damp meadows or even 

 finding its way up willow trees ; 60 to 80 eggs are laid in an 

 elliptical capsule. 



L. auricularia (the Ear-shaped Snail). — Is similar to peregra, 

 but the body whorl and mouth of shell even larger relatively 

 and more contracted by the penultimate whorl (Fig. 65). 

 Shell f inch to l^ inches long; 4 or 5 wliorls. Not so 

 common as peregra, but found in most parts of Britain ; eggs 

 laid in a double series embedded in a long band of jelly. 



L. truncatula (the Dwarfed Limnaea). — Shell |- to | inch 

 long. Whorls 4 to 5 ; suture deep, umbilicus distinct as a small 

 chink behind the reflected lip of the shell. Found in rather 

 muddy water, but also out of the water. (For connection with 

 the life-history of the Liver-fluke see p. 96.) Eggs laid 

 12 to 20 together, in jelly capsule in the mud; hatched in 

 16 to 20 days.i 



" The Flat-coil Snails." — These are aquatic 

 Planorbis ^^^^^^ having flat spirally coiled shells, each whorl 

 lying on the outer side of the one before, but in 

 close contact with it. The colour of the body and shell is 

 usually dark, and the single pair of tentacles non-retractile, 

 long, and thin. The foot is smaller and shorter than in 

 Limnaea with a blunter end. The breathing aperture is on 

 the left side, and the lobe of the mantle, close to the 

 aperture, is itself vascular and may function as a respiratory 

 gill below water ^ (Fig. 66, C). 



Planoi'bis arrneus (Common Trumpet Snail or Bam's-horn). — 



' There are several other species of Limnaea, but these are not very 

 common. 



2 J. W. Taylor, vol. i. p. 304, 



