48 MOLLUSCA OF SOMERSET. 
LIMN#ZA PALUSTRIS, Miller. (Plate V, 5.) 
A frequent species in marshes, margins of ponds and slug- 
gish streams. 
North. 
Rhines about Glastonbury, Shapwick, Highbridge, ete..! 
Weston district ; F. A. Knight. 
Clevedon ; Miss L. C. Jones. 
Ashton ; Wheeler. 
Kenn Moor; Cundall. 
Bath Canal; Kenneth McKean. 
Bath ; Jenyns Mus. Coll. 
South. 
Middle Chinnock, several ; J. Ponsonby. 
Old Canal, Wellington ; W. Gyngell. 
Var. elongata. Moquin- Tandon. 
Pennard Moor, Glastonbury ! 
Var. conica, Jeffreys. 
Yatton; MecMurtrie. 
Var. roseolabiata, Jeffreys. 
Clevedon ; Misses Hele. 
Yatton ; Bristol Mus. Coll. 
LIMNZA TRUNCATULA, Muller. (Plate V, 7.) 
Generally distributed ; frequent on the banks of ditches, 
streams, canals and rivers. This species is of special interest 
in that one stage in the life history of an only too well known 
parasite, Fasciola hepatica, the cause of the dreaded liver rot 
or “fluke” of sheep, is spent upon it. Fasciola hepatica is a 
flat worm which, in the embryo stage, leads a free aquatic life. 
Passing into the body of the mollusc, it spends the sporocyst 
stage in the lung cavity. Next, what is known as the redia 
stage is passed in the viscera, chiefly the digestive gland. It 
then escapes from the snail and the free cercarian stage is 
spent upon grass, on which it encysts itself. The grass is 
eaten by sheep, and the mature sexual stage (Distoma hepa- 
ticum) is developed from the cercarian stage in the bile ducts. 
This snail is most abundant in marshy clay lands subject to 
periodic flooding. The infection of the sheep usually takes 
place during a wet autumn, and the disease is at its height in 
the succeeding winter. Three million sheep died of the 
“fluke? in England in the winter of 1879-80. 
Var. elegans, Jeffreys. 
Frequent with the type in the Wincanton district. 
