FAMILY OF CHAMACEA. 



81 



Fig. 101. UNIO. 



We also place in this same group certain marine mollusks, 

 which resemble the Unios in their organization and the general 

 disposition of the hinge, but in which the beaks (summits) of 

 the shell are more arched, and from which projecting ribs 

 radiate towards the circumference ; such are the genus CAR- 

 DITA, the form of which is more or less oblong or cordiform 

 (heart-shape) ; the CYPRICARDIA, in which the tooth beneath the 

 summit of theshell is divided intotwoor three ; the CORALLIOPHAGA, 

 in which the shell is thin and the lateral plate much effaced, &c. 



26. In the FAMILY OF CHAMACEA the mantle is closed 

 and perforated by three open- 

 ings only; through the anterior 

 one passes the foot (fig. 102, 

 p) ; the next (r) gives passage 

 to the water necessary for res- 

 piration, and the third (e) is 

 for the expulsion of effete 

 matters. As we have already 

 stated, the last two openings 

 are not prolonged into tubes, P ( 

 as in the next two families. 

 And the hinge is very analo- 

 gous to that of the Unios ; for 

 the left valve has a tooth near 

 the summit, and funher back, a projecting plate, which are re- 

 ceived into fossa? (pits) in the opposite valve. 



Explanation of Fig. 102. A Chama divested of its shell to show the dis- 

 position of its mantle : p. the foot ; r. opening for respiration ; e. the 

 opening for the passage of excrement. 



26. What are the characters of the family of Chama'cea ? 



, WITHOUT ITS SHELL. 



