72 CATECHISM OF ICHTHYOLOGY. 



diameter, but they are by no means so palatable 

 as the small species. The oyster is remarkable as 

 producing that beautiful jewel called the pearl. 



Q. What is the Mytilus ? 



A. Of the Mytilus or Muscle, there are many 



varieties, some inhabiting rivers, others the sea j 



some excellent food, others nauseous and unwhole- 



ome. Unlike the oyster, it is not fixed to one 



ace, but can remove at pleasure, 



Q. What is the Pinna ? 



A. The Pinna is a shell fish which deserves no- 

 tice for this singular circumstance ; being blind, it 

 admits within its shell a species of naked crab, 

 which occasionally goes out to seek for prey j during 

 its absence, the shell of the Pinna remains open ; 

 the Cuttle fish seizes this opportunity to attack the 

 Pinna, when the crab, which goes to no great dis- 

 tance, hastens to the defence of its benefactor, the 

 shell is closed, and the enemy disappointed. 



Q. How many species of the Multivalves are 

 there ? 



A. Only three ; Chiton, Lepas, and Phloas. Of 

 the first, little is known ; the second is the Berna- 

 cle, found adhering to the bottoms of ships and to 

 piles driven into the sea, and the third is remark- 

 able for a phosphoric light which it emits, and 

 even imparts to the mouths of those who eat it. 



Printed by R. Gilbert, St. John's Square, London. 



