Lamarck's Geneta of Shells. ^17 



elongated, tubular, exsevtile, and usually armed with hard 

 parts. Mantle various, either ^vith the margms free, at the 

 sides of the body, or ^vith the lobes united into a bag which 

 partly envelopes the animal. 



Branehi^ various, rarely symmetrical, circulat.on double, 

 one particular, the other general. Heart unilocular, occa- 

 sionally with two divided, very remote auricles. No gan- 

 glionated medullary cor-l, but a few dispersed gangha, and 



different nerves. 



Body sometimes naked, either with no internal solid parts, 

 or enclosing a shell, or some hard substance; sometimes fur- 

 nished with an external covering, or ensheathing univalve shell. 

 Shell never composed of two opposite valves united by a 



ill II 2*6 



The distinguishing character of the mollusca, is that they 

 have no vertebr«., are wholly without articulations in all their 

 parts, and have a more or less prominent head at the anterior 

 portion of the body. 



The body of these animals is fleshy, soft, and eminently con- 

 tractile, and endowed with the power of reproducing the parts 

 that may have been destroyed. It is covered with a soft skin, 

 moistened by a viscous glutinous fluid, which continually 

 exudes from it; the skin forms the true covermg of the amraal, 

 and is wholly independent of the solid testaceous envelope. 

 The blood of the mollusca is white or bluish ; their muscles 

 are white and very irritable, attached beneath the skm to , 

 the substance of the mantle. The body is elongated some- 

 times oval, slightly depressed, sometimes straight, and some- 

 times spiral at the hinder part. They have no true lungs, but 

 respire by the branchiae. Their mouth is generally furmshed 

 with hard parts; in some it is short, and has two jaws ; m 

 others, it consists of a retractile trunk, with small teeth at its 

 internal orifice, but no jaws. The mollusca, which are fur- 

 nished with the trunk, as the buccina, volute, ^•^•' ^'■^ /=^.'^- 

 Bivorous, using it to perforate the shells of other shell-fish, m 

 order to prey on the animal within. Those with strong horny 



