GASTROPODS. 
05 
up like a rope, in the same plane. They frequent stagnant pools and ditches, or 
slowly running water, in all parts of the world. The well-known P. corneus is 
not only by far the largest of the eleven British species, but also larger than any 
common pond-snail ( Limncea). 
other known form, although some of the South American types approximate 
closely. When disturbed, it emits a purple-coloured fluid, probably as a means 
of defence. 
In Physa the animal is always sinistral, having the respiratory and genital 
orifices on the left side. The tentacles are cylindrical, and the eyes are at their 
1, Limncea glabra ; 2, L. palustris ; 3, L. stagnalis ; 4, L. truncatula ; 5, L. peregra ; 6, L. vulgaris: 
7, L. ovata ; 8, L. auriculciria. 
inner base, as in Limncea. The mantle is furnished on each side with more or less 
elongate lobes, which, when the mollusc is crawling, are folded back upon the 
exterior of the shell. In their habits these snails resemble the preceding genus, and 
they are almost cosmopolitan in their distribution. Physopsis, a Central and South 
