54 THE LIFE OF THE MOLLUSCA 



under surfaces of big stones. The Mussels, as well 

 known, attach themselves to the rocks by their stout 

 byssus threads, their clustered masses affording 

 secure shelter to many lesser animals ; while in 

 mangrove swamps the Oysters will attach them- 

 selves to the branches of the trees that dip in the 

 water at high tide — a fact which was observed and 

 recorded by W. Smith at Sierra Leone in 1726. 



Periwinkles, Top Shells (Trochidse and Turbinidse), 

 and other holostomes, haunt the tangled masses of 

 seaweeds ; while among the siphonostomes are the 

 Dog- Periwinkles (Purpura), Dog- Whelks (Nassa), etc., 

 all stout-shelled forms capable of withstanding con- 

 siderable buffeting amid the waves. The Piddock, 

 or PholaSj Saxicava, Lithodomus, and other boring 

 molluscs, excavate burrows in various rocks, in coral, 

 and even the shells of their bigger confreres. Others, 

 like Tapes and Coralliophaga, too lazy to make their 

 own retreats, take possession of the deserted burrows 

 of others. The latter generally selects the crypt of 

 a dead Lithodomus, which it closely resembles in 

 shape (Plate XXXII. , Figs. 17 and 18), and the 

 shells of successive generations of Coralliophaga, 

 packed one within the other, will be found lying 

 between the valves of the original architect of the 

 home. In the cracks and crevices of the rocks the 

 Octopods hide. The majority of the Pelecypods, 

 such as the Cockles, Ark-Shells, Tapes, etc., remain 

 more or less buried in the sand or silt, the Razor-fish 



