PHYSA. 125 
present known, but will probably be found to consist of 
some favourite food-plant. 
This species like many of the Zzmn@e@ has the habit 
of floating on the surface of the water with its footsole 
uppermost and exposed to the air. 
Var. I. mdjor (Charp.). Length 18 mm. 
Var. II. riéibra (Tryon). Dark reddish. 
Monst. decolldtum (Nelson). Decollated. 
Genus. —PHYSA Draparnaud. 
Mantle having lobes expanding over the shell. 
P. FONTINALIS (frequenting springs) Linné. Pl. VIL, f. 14. 
Sinistral, oval, very thin, glossy, semi-transparent, greenish horn- 
colour; whorls 4 to 5, tumid; spive very short, obtusely pointed. 
The deeply serrated mantle is extended over most of the shell. 
A.gmm. B. 63 mm. 
The “Bubble Shell” is more common than the last, 
and is more abundant where it occurs, and frequents 
running as well as still-water. It has a great partiality 
for the under sides of the water-lily. 
Though the last species and several other members of 
this family spread threads of mucus in the water, 7. 
fontinalis is facile princeps in the art. This *habit may 
be well watched in an aquarium, where the threads may 
be seen passing perpendicularly downward from the sur- 
face of the water, and upward from the bottom. The 
“See an interesting paper by Mr G. Sherriff Tye, in F.C., vol. 1. p. 104. 
