Historical Account of Testaceological TJ^riteH. 177 



limited in the choice of generic characters. But to the estabUsh- 

 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 verj' 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 unshapen 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 Avith 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, 

 in other 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 Avhole 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, 



