NATURAL HISTORY. ti 
The shell, which is perfectly transparent, 
consists of a single piece, no hinge or joint 
being perceptible; it, notwithstanding, pos- 
sesses sufficient elasticity to permit the animal 
to open it at pleasure, in a manner similar to 
the common muscle (Mytillus edulis). The two 
edges of the opening are seen in the drawing 
near ¢, plate 3, figure 3, which represents a 
magnified side view of this creature. The two 
eyes (a) are of different magnitudes, and their 
black colour forms a striking contrast to the 
surrounding parts. They are embedded in the 
shell, and consequently protected by it. The 
rostrum, or beak (4), is pointed, and partakes 
of the general convexity of the shell. Beneath 
this. is situated another process, similar in ap- 
pearance, but shorter; atits extremity are three 
setaceous bristles, which probably perform the 
office of palpi; below these are situated the 
two antenne (c), each terminated by similar 
bristles, butlonger. The false feet, or branchee, 
are four in number, and disposed in a single 
row within the shell; they are hirsulate, and 
terminate like the antenne. When in motion 
they cause the animal to revolve, which it can 
accelerate by the action of the process (d) 
against the water. At other times the false feet 
