e& 
15 
The common mussel, Mytilus edulis Linné, (figs. 6, 7) is 
smooth, varying in color from black to light yellow. The 
lighter specimens frequently have radiating green lines and 
stripes and are very beautiful. Mussels are considered edible, 
but Iwould not recommend them to anyone but book-reviewers 
and other natural enemies of mankind. 
Closely related to these are the 
Horse mussels, Modiola plica- 
tula Lam. They have the beaks 
a little distance from the narrow 
end of the shell, not at the end 
as Mytilus has. ‘The larger end 
of the shell is finely fluted, as 
well as a little triangle at the 
smaller end. They are found 
living where there is an admix- 
ture of fresh water. - 
Fig. 9g. Arca transversa. 
The Ark Mussel family or 
Fig. 8. Modiola plicatula. ~ Arcide have the beaks near the 
middle of the hinge line, the two adductor muscles equal, the 
hinge furnished with many very fine interlocking teeth, like 
fine comb teeth. The outside is fluted like a cockle. They 
