144 DIVERSIONS OF A NATURALIST 



Though " shells " are often numerous on parts of the 

 seashore, some beaches (as, for instance, at Falmouth, 

 at the mouth of the Eden of St. Andrews, and at Herm 

 in the Channel Islands) being so placed in regard to the 

 currents and waves of the sea that great quantities of 

 shells of dozens of species are thrown up, and even 



c. 



d 



FIG. 19. Some British Marine Bivalve Molluscs. 



a, The smaller Piddock, Pholas parva, which bores into chalk, clay, 



and hard rock. Natural size. 



b, The Razor- shell, Solen siliqua. The muscular foot is seen protruding 



from the shell. One-third the natural size, linear. 



c, Venus verrucosa. Natural size. 



d, Cardium echinatum. Two-thirds the natural size, linear. 



e, Pinna pectinata, the " cappy longy." One-fifth of the natural size, linear. 



" make up " the beach, yet there are not so very many 

 Molluscs which live commonly on the shore between tide- 

 marks. The shells which are accumulated as shell- 

 beaches have come from animals which lived in quantity 

 at depths of ten or twenty fathoms, whence they can be 

 brought up alive by the dredge. There are, however, 

 certain bivalves and certain univalves which are com- 

 monly to be found in the living state between tide-marks. 



