248 ELEMENTARY ZOOLOGY 



along coasts are found here and there great mounds 

 made of heaps of clam-shells which have become covered 

 over with soil and vegetation. Such mounds are the old 

 feasting-places of the early coast inhabitants, and the 

 archaeologist often finds in these "kitchen-middens," as 



FlG. 104. A group of marine Pacific Coast molluscs; in upper left-hand 

 corner. Piirpura saxicola; next to the right, Littorina scutiilata,', 

 farthest to right, limpets, Acmara spectrum; left-hand lower corner, 

 Mytilus calif orni anus; in right-hand lower corner the black shells just 

 above the large clam-shell, Chlorostomum fitncbralc. (From living 

 specimens in a tide pool in the Bay of Monterey, California.) 



they are called, various relics of the early natives of the 

 continent. 



Even more widely known that the clams are the oysters 

 (Ostrea virginiana], also members of this class of mol- 

 luscs. The oyster is carefully cultivated by man in many 

 countries. It has its two shells or two shell-halves dis- 

 similar, one valve being hollowed out to receive the body, 

 while the other is nearly flat. The oyster is attached to 

 the sea-bottom by the outside of the hollowed-out valve. 

 When first hatched the young oyster swims freely by 

 means of its cilia; after a few days it attaches itself to 



