268 MOLLUSCA, 



found together, and fhey are most prolific. One may find them 

 at all times of the year. The shells are elongated and conically 

 oval, the spire being produced, while the snail's body is twisted 

 up in the spire of the shell They have a prominent head and 

 an oblong foot, notched in front and rounded behind. The 

 shells are extremely variable, one species {Limmeus pereger) 

 having at least fourteen varieties. In this country the two 

 species important to us are L. truncatulus and L. 'pereger. Both 

 are hosts of the liver-flukes {Distnmidw), especially the all- 

 important liver-fluke {^Distonmm hepaticum) vt'hich causes the 

 " liver-rot '' in sheep. 



L. truncatulus (fig. 140, a) is a pale ashy-grey turreted shell 

 with five or six whorls, the last whorl being large and expanded, 

 and occupying about three-fifths of the 

 shell ; the spire tapers to a very fine 

 point. It is found nearly all over 

 Britain and Europe, Afghanistan, Mo- 

 rocco, Algeria, the Canary Islands, &c. 

 This snail lays its ova or spawn upon 

 F,a. 140.-WATER-.NM.S mud around ponds, ditches, and 

 (Limntrida). streams. Each snail lays about 1500 



x.^e™^r"^vS™t"i^; "' ova, in batches of 30 to 100. Th^y 

 are deposited in strips of some gelatin- 

 ous substance. Incubation takes place in about two weeks. 

 This is the chief host of the liver-fluke. 



L. pereger (fig. 140, b), the other fresh-water snail, is almost 

 transparent yellowish - brown, and spiraUy striate, with five 

 whorls. This species often wanders far from water, and may be 

 found crawling up wiUow-trees and in damp meadows. They 

 are carnivorous in habits. Although the embryos of the liver- 

 fluke are found in this species, it seems it cannot complete its 

 changes in it. Were there no Liranseidae there would be no 

 liver-rot in our flocks ; but it is extremely diflicult to destroy 

 these molluscs. There is no doubt that the suggestion made by 

 Miss Ormerod of clearing out shallow pools of weeds, and re- 



