6o 



MOLL USC A, 



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 (Aspergillum). 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. 



FIG. 63. The interior of a univalve 

 (Periwinkle), f, foot ; m, muscle 

 for drawing back into the shell ; 

 g, spittle glands ; the glands for 

 giving out slime are near the anus 

 tube ; ///, throat leading to s, 

 stomach ; r, tooth-bearer rolled 

 up ; br, branchiae or breathing- 

 gills, which, when the mantle is 

 folded back in its place, lie over 

 the throat ; a, anus ; 0, ovary car- 

 rying eggs, 



Class I. SNAILS, etc. 

 (Gasteropoda, belly- 

 footed). 



General Characteristics. 

 Mollusks that secrete a 

 single shell. They have 

 ears and eyes upon a dis- 

 tinct head. The foot is 

 now a flat, creeping disk 



