MOLLUSCS 115 
An examination of one or two shells will make the 
matter clearer, 
Let us take for investigation the well-known form Venus, 
any species of this genus will do, and specimens are avail- 
able on most of our coasts. 
The shell is brown in colour, nearly spherical in shape, 
and marked on the 
outside with concen- 
tric furrows—which 
in the form figured 
are crossed by lines 
radiating from the 
beak. The beak is 
placed towards the 
front—and_ the liga- 
ment is on the out- 
side of the shell, or 
Fig. 76.—Left valve Venus (outside). external. 
Inside, the impressions marking the attachment of the 
adductor muscles are plainly visible, and the pallial or 
mantle line is broken towards the back margin by a little 
opening or sinus. 
The hinge line is strengthened by the presence of three 
teeth which fit into as many corresponding grooves, and 
add greatly to the force with which the valves are held 
together. 
Another common bivalve is the Scallop (genus Pecten) 
found in considerable numbers on many of our sea beaches. 
In colour the shell is reddish brown, and in shape nearly 
circular. The valves are unequal and dissimilar, the right 
valve being convex and the left almost flat. The beaks 
are close together and eared—the ears on the right valve 
being most prominent. The outside of both valves is 
