[Bu Theo. Carreras. 
THE ROCK-SHELLS JN SITU. 
Three kinds are here grouped together. In the background is the Magilus, who has extended his shell to prevent interment 
in the steadily growing coral. To'the left is the Common Piddock in his burrow, showing the hinge-plates which strengthen his 
hard but brittle shell. To the right is the Date Mussel, which, in order to suit itself to its burrowing habits, has departed from 
the usual mussel shape and developed into a long cylinder with rounded ends. 
