LECTURE XL ^ 
183 
The Multivalves are distributed by Linnaeus into 
three genera, one of which, named Pholcis, has the 
general appearance of a bivalve but on close in- 
spection, will be found to dijffer; having small or 
accessorial valves or pieces at the back part of the 
siiell. The inhabiting animal resembles an Asci- 
dia. The most common species of Pholas is the 
P kolas Dactylus of Linnsus, a native of the Euro- 
pean seas : this species has the faculty of piercing 
and imbedding itself in calcarious rocks, in which 
it is generally found : the animal is considered as 
an edible shell-fish, and in some places is regarded 
as a delicacy. 
The next genus is of a very singular appear- 
ance, and is called Chiton. It is of an oval sloape, 
and is composed of several transverse pieces; those 
at each extremity having a rounded outline. The 
inhabiting animal is shaped like a Poi'is or Sea- 
SnaiL The species of Chiton are pretty numer- 
ous, and there is a considerable degree of general 
similarity between them. One of the largest is the 
Chiton squamosus, measuring about three inches in 
length, and of a greenish white colour. It is a 
native of the American seas ; but several of this 
genus are found also about the European coasts. 
