CONCHIFEBA. 



259 



The Conchifera may be classed in accordance with 

 the following Table : 



[Having the mantle open, and without tubes or OSTRACEA 

 special apertures Oysters. 



Open in front and having] 



but one separate aperture I MYTILACEA. 

 for the escape of effete | Mussels, 

 matter J 



Not p r o- 

 longed so 

 as to. form 

 tubes. The 

 mantle 



Closed and pierced by three' 

 apertures, the first of 

 which serves for thet 

 passage of the foot, the! 

 second for respiration, j 

 and the third for the exit 

 of excrementitious mate- 1 

 rials J 



CHAMACEA. 



Clams.' 



Prolonged so 

 as to form 

 tubes. The 

 mantle 



Open in front and present- j CARD I ACE A, 

 ing two tubes behind . j Cockles. 



Closed and having in front 

 or below only a single 

 opening forthe passageof 

 the foot, and two tubes! 

 behind 



INCLUSA, 



Borers. 



The first family of the Conchifera includes Oysters 

 (Ostracea) ; these have no foot, and the mantle is 

 entirely open; the shell is irregular, thick and 

 foliated, and is generally fixed to some foreign body 

 by the outer surface of one valve. The hinge is 

 toothless, and the ligament is internal. 



The Common Oyster. " The living luxury " is too 

 well known to need description. 



The Tree Oyster (Ostrea arborea), which in Africa is 

 met with clinging in clusters to the exposed roots of 

 the mangrove-trees that fringe the margin of all the 

 great rivers in tropical climates, is, according to 

 Adanson, as delicate and well tasted as our own. 

 The negroes lop off a branch loaded with the shells, 



