234 



ZOOLOGY 



shell was used as money (" wampum ") by the Indians. The 



shell is extremely heavy, and 

 usually nearly circular in outline 

 (Fig. 223). 



The arks (Arcidae ^) and their 

 allies include several species hav- 

 ing a more or less elongated 

 hinge-joint crowded with many 

 small teeth. Our common East- 

 ern species {Area pexata, Fig. 



224) has bright red blood and is commonly known as the 



" bloody clam." 



The mussels (MytilidiB ^) are the familiar blue black, wedge- 



FiG. 224. — Area pciata, the liloody 

 clam. Nat. size. Photo, by 

 W. H. C. P. 



Fig. 22.5. — Bit of bed of mus'5i4s lying at base of the marsh-grass iSpartina), 

 exposed at low tide. At rising tide a swift current flows over this bed. 



^ area, an ark. 



' mytilos, an edible mussel of the Greeks. 



