87 
nlament, which it attaches to some floating body, and 
by which it lowers itself dowm from the surface to 
the bottom of the pond ; but it only seems to resort 
to that occasionally, when no easier method of getting 
down is at hand, such as the stalks of acquatic plants. 
2, P. liypnorum can scarcely be classed among the 
pond mollusca, for it is generally found on plants in 
running streams. This species is also of a lively 
nature, and is said to repulse wandering animals with 
repeated blows inflicted by a rapid movement of its 
shell, the foot being the point of fixture. 
The third genus is Lymncea which has the shell 
conic-oval or elongated. 
1. luymncBa i:feregra or limosa has a spiral shell 
formed of five wdiorls, very thin, semi-transparent, 
and horn coloured. It is the commonest of all fresh 
water mollusca, and is found in almost every pond. 
2. LymnxBa truncatula has a longer shaped shell of 
five or six w^horls, mucli thicker and stronger than 
the shell of gperegra, and very often covered with a 
coating of hardened mud. It is found in the pond at 
the top of the North Inch and several other localities, 
but it is not nearly so common as the peregi'o.. 
3. - LymncEa palustHs a yellowish brown shell 
of from six to seven whorls, and is found a.11 over the 
district. All these three species are common through¬ 
out Britain. 
Of the fourth genus Ancylus, there are two species 
in the district,— 
1. A. fluviatiliSf or the fresh-w*ater limpet, can 
scarcely be called a pond mollusk, for it is generally 
found on stones in running streams. It is, how*ever, 
abundant in Loch Tay and Loch Tummel, and several 
other localities. Its food is fresh-water algte, and 
decayed vegetable matter. 
2. A. lacustris is a longer shaped species, is more 
active in its habits, and instead of being found on 
stones in running streams, it is got on stems of 
aquatic plants in ponds. It is found in Moncriefle 
Pond, and in a pond near Dupplin. 
It will be seen that the fresh-water mollusca are 
not veiy numerous, and would form an interesting 
and easy subject of study for any member, who. 
