Handbook of Paleontology 129 



and some varieties require more sheltered places. The 

 two species are not found together. The Limpets 

 have flat tentlike shells and are well represented on 

 both coasts of the United States. The Tortoise-shell 

 Limpet (Acmaea testiidinalis) is exceedingly common 

 on the New England coast clinging to the rocks be- 

 tween tides. It ranges from the northernmost waters 

 to New York. When cleaned the shell shows a mot- 

 tled coloration of pale green, brown and white. A 

 smaller, more fragile variety, exceedingly common 

 along the New England coast, lives on eel-grass. It 

 has brighter coloring — reddish brown spots on a 

 white surface. 



The most noticeable bivalve is the Common Edible 

 Mussel (Mytilus edulis) which lives in colonies be- 

 tween tides from North Carolina to California and is 

 also common on arctic shores and the northern coasts 

 of Europe. It is exceedingly abundant along the New 

 England coast, so much so that in places it blackens 

 the shore. Great masses of these shells cover shallow, 

 sandy and muddy flats ; they are also found in gravelly 

 situations and in pebbly stations among large rocks. 

 The shell of this species is two and a half inches long 

 and violet in color, but the color of the epidermis is 

 black or deep blue. A variety found associated with 

 the typical form has a shell that is brightly rayed in 

 green and yellow. These mussels are attached by 

 strong, yellow-colored fibers, the byssus, secreted by 

 a gland in the foot. 



'Crustaceans are well represented in rock pools. One 

 of the conspicuous forms is the Rock Barnacle, Acorn 

 Barnacle or Sea Acorn (Balanus balanoides) that in- 

 habits the Atlantic shores of Europe and America from 



