60 MOLLUSCA. 
author several years ago, has now disappeared, having crumbled away 
under their tunneling. Hulls that appear solid may be crushed by the 
hand—completely honey-combed. ’In 1731 they nearly destroyed the 
piles in Holland, threatening the country with destruction, They 
attack floating wood, and so are carried all over the world. Docks at 
Tortugas, Fla., were rendered unsafe in twelve months. Palmetto is 
the most successful resistant. 
Watering-pot Shells (4sfergi//um).—In these shells 
the two valves are imbedded in the lower part of the tube, 
the beaks only being visible 
externally. The tube which 
incloses the siphon ends in 
shelly expansions or ruffles; 
at the other or anterior end 
it is club-shaped, and cov- 
ered by a disk like the nose 
or sprinkler of a watering- 
pot, and perforated with 
numerous holes in exactly 
the same way. They are 
found in tropical countries, 
buried in the mud or sand, 
the ruffled end containing 
the siphon exposed. 
SINGLE-SHELLED MOL- 
LUSKS. 
Fic. 63.—The interior of aunivalve Class I.—SNAILs, etc. 
(Periwinkle). jf, foot; mt, muscle (Gasteropoda, belly- 
for drawing back into the shell; 
footed). 
&, spittle glands; the glands for 
giving out slime are near the anus py 
tober PA, threat leading: 16: General Characteristics. 
stomach ; 7, tooth-bearer rolled —Mollusks that secrete a 
up; 4r, branchiz or breathing- single shell. They have 
gills, which, when the mantle is ears and eyes upon a dis- 
folded back in its place, lie over . r 
the throat; a, anus; 0, ovary car- tinct head. The foot is 
rying eggs. now a flat, creeping disk 
ping 
