84 THE SHELL-FISH OF THE COAST. 
on the interior of the shell connects the adductor 
impressions. This sinual inflection, or ‘pallial sinus,’ 
is one of the most important characters to be noted 
in the shell, since it serves to indicate a prominent 
feature in the structure of the animal. 
We recognize two hard-shell clams on our coast, 
one having an obliquely oval shell, the quahog 
(Venus mercenaria), and the other, with a more nearly 
SURF-CLAM (Mactra solidissima). 
triangular or equilateral shell, the Mactra (Mactra 
solidissima). ‘The former is the edible species, al- 
though by some the Mactra is not completely de- 
nied a hearing. The latter, also known as the 
‘sea-clam’ or ‘surf-clam,’ inhabits the sandy coasts, 
where it lies buried just beneath the surface; 
but it may be occasionally seen skipping about 
