con cue logy. 



REMARKS. 



The general divisions of Testacea or Shell Animals, 

 may be classed under the following Orders : Spirales, or 

 Shells which have a twisted spire : Acuminata?, or pointed 

 Shells, as the Patella, &c. : Bivalva?, or double Shells, as 

 the Cockle, &c. s and lastly, Mnltiloculares, or Shells 

 having bony compartments, as the Orthoceras, Nautilus, 

 &c. Those which were denominated by Linnncus^Multi- 

 alva?, are not found upon Analysis to consist of similar 

 component materials, and therefore ought properly to be 

 separated ; such are the Sabella?, Chitons, &c. These 

 latter are rather to be considered as Animals invested with a 

 horney or membranaceous Covering, rather than Testaceous 

 or Shell Fish ; to which may be added, a very considerable 

 difference in their internal Organization. 



Philosophers have been much perplexed to account 

 for the Manner of the growth of S3iell-fish ; and notwith- 

 standing that matter has received a very copious Investiga- 

 tion, it is still involved in considerable doubt. It was once 

 believed that the animal had the power of adding an exter- 

 nal Coat or Flap to the side of the Mouth, and which was 

 repeated at certain intervals, enlarging the circle and size 

 of the shell as the Animal increased in magnitude. Other 

 writers have supposed that the Animal had the power of 

 forming a new Covering for itself, and totally deserting the 

 former shell when it became too small. It seems more pro- 

 bable that the Shell has an internal Power of Growth or 

 Expansion, which exists from its beginning or birth, and 

 adapts itself by a general Expansion to the Size of the 

 Animal. Certain it is, that when the Animal is arrived to 

 its utmost size, it has the power of spreading over the 

 whole Surface of its Mouth a substance of the smoothest 

 Enamel, which serves at the same time to thicken and en- 

 large the Lip ; particularly the Strombus and Cowry. 



