COCKLES. 269 
mary ones called cardinal are oblique, and one 
lateral remote on 
each side. The 
valves are almost 
always — covered 
with well marked 
ribs — alternating 
with furrows, 
which radiate from 
the beaks to the 
margins. ‘These 
ribs are sometimes 
studded with spin- 
ous seales. The 
ligament is exter- 
nal and conspicu- 
ous though short. 
The animal is 
shaped much like 
the shell, being 
round and swollen, 
with the mantle 
open in front, the 
edges of which are 
usually plain, but 
strongly fringed in 
the neighbourhood 
of the two siphons; 
the latter are short, 
slightly separated 
and fringed around 
the edge. The foot 
is very large, cy- 
lindrical, with a 
FOOT-MUSCLES OF COCKLE. 
conical tip directed forwards. It is bent, with an 
