MUSSELS, AND! PECITENS 
Je) 
Or 
length is three or four inches, but a variety flabel- 
lus, Gld., found in British Columbia and in deep 
water off the coast of California, grows to a much 
larger size. 
Modiolus fornicatus, Gld., Arched Horse-mus- 
sel, has a very short and full shell, somewhat 
wedge-shaped, having a breadth more than half 
of its length. The naked shell is white, though 
sometimes tinted, and it is normally covered with 
a light brown epidermis, especially near the edges. 
This shell is sometimes found solitary, but at 
Fig. 16 
other times in large masses, grouped around the 
base of a seaweed, or in some similarly protected 
situation. The common length is about an inch. 
Modiolus plicatulus, Lam., the Plaited Horse- 
mussel, is really an Atlantic species, being ex- 
tremely abundant formerly in the ‘‘ Back Bay’’ of 
Boston, a spot now covered with beautiful streets 
and fine buildings. It doubtless came to Califor- 
nia with seed oysters, which were planted in San 
Francisco Bay, where it may now be found in con- 
siderable numbers, and where it may ultimately 
become as abundant as it was in Boston. It has 
a rather pretty shell, about two inches long, with 
a glossy epidermis. It is marked by a great num- 
ber of small but very distinct plaits or ribs, radiat- 
