100 A HISTORY OF RECENT CRUSTACEA 
one that hunts the Pinna, and, in accordance with this 
designation of the genus, Oppian tells the story that when 
oysters open their valves to take in the mud and water on 
which they live, one of these crafty little crabs picks up a 
pebble and thrusts it in, so that the oyster is prevented 
from closing its shell again, and the crab enters and feeds 
upon its nutritious flesh. Gesner in the sixteenth century 
expressed his confidence that this was mythical, smce you 
never find any bites upon the mussels, pectens, pinnas, 
and oysters that are attended by these crabs. 
The name Pinnotzres means one that watches or guards 
the Pinna, and there can be little doubt that it was the 
form used by Aristotle, seeing that he also speaks of it as 
Pinnophijlax, a word of precisely the same meaning. Not 
only Aristotle, but many succeeding writers of renown, such 
as Cicero, Pliny, and seemingly Linnzeus himself, accepted 
the opinion that there was a compact between the mollusc 
and the crustacean for their mutual benefit. Whenever 
little fishes swam in between the expanded valves of the 
mollusc, it was supposed that its companion gave it a little 
friendly nip, upon which the valves snapped together, the 
prey was secured, and shared between the confederates. 
A similar policy was pursued to exclude the intrusion of a 
dangerous foe. The great antiquity of the belief is at- 
tested by the fact that the Egyptians in their hieroglyphics 
made use of the pinna and crab to symbolise the helpless- 
ness of a man without friends. That the belef was un- 
tenable was pointed out by many naturalists from Gesner 
down to Cuvier, on the ground that molluscs do not feed 
on little fishes, and that the residence of the crebs within 
the valves was sufficiently explained by the prevailing 
softness of the carapace in this family. This indeed ap- 
plies chiefly to the females, and it is the females that 
appear to be most frequently found thus domiciled. 
It is so much the nature of crustaceans to take refuge 
in any sort of cleft.or cranny that the first entrance of the 
Pinnotheres into any sort of bivalve can be easily under- 
stood. When the residence proved to be peculiarly secure, 
the shell of the crab wonld by degrees lose a hardness that 
