ORDER GASTEROPODA. 57 



transversely into several distinct moveable pieces, to give 

 greater freedom to the animal in its movements." 



The Chitons, like the neighbouring genera, frequent 

 the rocks between high and low water mark, but are 

 much more active in their movements. Pull, a learned 

 Neapolitan, in describing the anatomy of a Chiton, says, 

 that the interior of the mouth or throat of this animal is 

 covered with a multitude of teeth, — some simple, and 

 others with three points, and that these teeth are dis- 

 posed in numerous longitudinal ro'>ys. 



CLASS CONCHIFERA. 



The Conchifera differ from the Molluscous animals that 

 bear shells, in a very great degree; for, although the 

 substance of the body is soft, unlike the Mollusca it is 

 inarticulate, always enclosed in a shell of two valves, 

 without head or eyes,— a mouth, if it may be so called, 

 concealed from view, and without any hard parts, and 

 the whole body enveloped in a large mantle, or hood, 

 formed of two thin lobes, generally perfectly free, but at 

 times united in front; these are the principal distinguish- 

 ing characters of this class. 



In earlier systems, when shells were classed without 

 much reference to the animals that inhabited them, the 

 only distinction made was the number of pieces of which 

 the shell was formed, and they were arranged under the 

 heads of univalves, of one piece, bivalves, with two pieces, 

 and inultiialves, with moie than two pieces. Tiiis ar- 

 rangement was inconvenient, a*, in some cases, it se- 



