LECTURE XI. 
iiig beyond its usual limits^ is capable of destroying 
the most boasted efforts of human industry. About 
the year 1730 the most flourishing republic in 
Europe was made to tremble at the name of this 
seemingly insignificant creature j the Dykes of 
Holland during that year exhibiting such marks 
of decay in many parts, where they had been 
attacked by these animals, originally introduced 
by ships from the East Indies, that great appre> 
hegasions were entertained of the Dykes giving way, 
and exposing the country to the ravages of the 
ocean. 
The last Linnsean genus of the Univalves, the 
Sabdhiy is improperly placed among the shelly 
tribe; since the tubular structure, by Linnaeus 
called the shell, is merely composed of aggluti- 
nated grains of sand, lined by a connecting mem- 
brane. The inhabiting animal is allied to the 
genus Nereis among the naked Mollusca. 
Proceeding to the Bivalve Shells, we shall ob- 
serve that the chief instances in which the inhabit- 
ing animal differs in character from the rest, are 
those of the genera entitled Anomia and Pinna. 
Of these the genus Anomia is inhabited by an ani- 
mfJ whose nature is not yet fully ascertained; and 
