242 



8UBKIKGDOM MOLLUSCA. 



Mollusca vera 



HEAD AND FOOT . 

 PRESENT ; 



Bl- LATERALLY SYMME- 

 TRICAL ; FEET AROUND 

 THE HEAD. 



LATERALLY UNSYMME- 

 TRIOAL; FOOT BENEATH 



THE BODY 



HEAD ABSENT ; FOOT PRESENT ; 



Molluscoidea. j 



SHELL, DORSAL, AND 

 VENTRAL VALVE. 



LEATHERY, ELASTIC COV- 

 ERING ; SIMPLE OR 

 COMPOUND. 



COMPOUND ; MOSS-LIKE. Polyzoa. 



CLASSKS. 

 Cephalopoda. 



Gasteropoda, 



Lamellibranchiat 

 Brachiopoda. 



Tunicata. 



CLASS I. CEPHALOPODA. 



General Characteristics. The Cephalopoda (head- 

 footed) have muscular tentacles or arms around the mouth ; 

 beaked, horny jaws; two large eyes: arms covered with 

 sucking discs ; and a bag of ink, with which most species 

 blacken the water to hide from pursuit. 



CEPHALOPODA. 



ORDERS. 



TWO-GILLED. Dibranchiata, Argonaut, etc. 



FOUR-GILLED. Tetrabrancbiata, Nautilus, etc. 



ORDER DIBRANCHIATA. 



General Characteristics. The Dibranchiates (two- 

 gilled), have an ink-gland and the power of changing color 

 like a chameleon. 



Fig. U16. 



Argonauta argo, Paper Sailor. \. 



The Argonautidae (sailors) are named from the fabulous 



