AIR-BREATHERS 147 
and full, columella marked with very large and 
peculiar white folds. Surface light brown, length 
one-fourth of an inch. 
Siphonaria peltoides, Cpr., the Shield-like Si- 
phon-shell, has a limpet-shaped shell, small, thin, 
and low arched, with the apex a little to one side of 
the center. The color is light brown with more or 
less darker rays, and its length is one-fourth of an 
inch or more. The interior muscle-scar is divided 
on one side by a siphonal groove, but this mark 
is not always very distinct. This little mollusk 
lives on rocks between tides, and is quite rarely 
found. When disturbed it gives out a milky fluid. 
Gadinia reticulata, Sby., the Netted | 
Gadinia. The natural size of the shell is 
shown in Figure 126. It is low-arched es 
and has a nearly central apex, from 
which run radial lines to the edge of the 
shell. These rays are crossed by deep lines of 
growth, giving the shell a netted or reticulated 
appearance. Its color is pure white, and the shell 
is quite solid. I have found a few specimens liv- 
ing on mussel-bearing ledges, near low water line, 
but it is not often found alive. Dead shells are 
often washed up from the sea by the waves. Live 
Specimens are said to be abundant at Pt. Lobos, 
Cal., in a tide grotto. 
Leaving the sea for a time we now turn our at- 
tention to the air-breathing mollusks that live in 
fresh water. Though in general they come to the 
surface to take a breath of air, yet they are very 
tolerant of restraint, and some seem to be able 
to live in the water continually. They are quiet, 
Fig. 126 
