Historical Account of Testaceological Writers. 177 
limited in the choice of generic characters. But to the establish- 
ment of characters purely zoological the objections are still 
stronger than to the being guided by the general form of the 
shell. Independently of the very small extent to which our know- 
ledge of the Mollusca has hitherto been carried, it appears to us 
that, from the very nature of these animals when provided with 
a portable place of retreat from danger, they can never present 
those permanent and obvious points of distinction so indispen- 
sable to an apt and commodious investigation of all natural ob- 
jects. Wherein does the animal differ from an unshapcn mass of 
lifeless matter when coiled up within its shelly habitation ? And 
how are its natural shape and appendages to be examined, but 
by the knife of an anatomist ? In fact, it is reasonable to con- 
clude that innumerable testaceous animals must ever remain un- 
known to us, except by the exuvice accidentally thrown upon the 
shores after their death: many of them appear to inhabit in- 
accessible recesses of the ocean, and others part with life on the 
point of being removed from their native element. To place his 
system beyond the reach of those objections which presented them- 
selves to all that had been hitherto proposed, Linnaeus was obliged 
to strike out some principles of discrimination wholly different 
from any before exemplified; and that sagacity with which he 
seized new and admirable guidances to methodical arrangement, 
mother parts of the dominions of nature, fortunately assisted him 
also in this. After having convinced himself of the futility of 
forming a system of Testaceology solely on the structure of the 
animal, or even making the latter at all concerned in the specific 
distinctions, he astonishingly simplified the whole science by di- 
viding Testacea only into the three obvious families of Univalves, 
Bivalves, and Multivalves, with subordinate genera characterized 
by variations of particular parts of the shells. The hinge in bi- 
vol. vii. 2 a valves, 
