538 



regular fyftem, from the very little knowledge hitherto 

 obtained of them ; and as the more durable parts of fuch 

 animals \s-ere fo eafilv preferved, and fo extremely covet- 

 ed from their attratlive beauty, it became neceffary to 

 throw them into fome fvftematic arrangement, in order 

 that the fpecies might be afcertained, and names given 

 them, for the more ready communication of naturalifts 

 on the fubjeft. Indeed, could we afcertain the feveral 

 fpecies of animals inhabiting (hells, we are inclined to 

 believe, they would flill continue to be divided and fub- 

 divided by the form and ftruclure of their coverings, as 

 much as the Tortoife, Echinus, or the more cruftaceous 

 animal the Cancer, whofe bones are external. It muft, 

 however, be admitted, that the animal inhabitants of 

 fliells may, as far as thev can be afcertained, be an ef- 

 fential aid in difcriminating fpecies. 



The animals inhabiting fhells, as far as we yet know, 

 are confined to a very few genera, as may be feen in our 

 generic defcription of fuch ; fome of which are found in 

 a mollufcous ftate, and are properly feparated. On the 

 contrary, as the tubes, or cafes, ufually called fabellce, 

 are of that fragile, imperfeft, and perifliable nature 

 without being readily definable ; a covering from agglu- 

 tinated pebbles, to a thin tranfparent film not preferv- 

 able; we mull fyftematize the animals and not their oc- 

 cafional coverings, (from which many of them retire at 

 pleafure, and all independent of them) and endeavour 

 to make fuch fubfervient to fpecific purpofes only. 



Let 



