LAMELLIBRA.NCHIATA. 533 



Family Cardiadcp. 



Pedal orifice large ; siphons usually short ; foot large, sickle- 

 shaped. Shell equivalve, cordiform ; cardinal teeth 2, lateral teeth 

 1, 1, in each valve. 



Genera Cardium, Hemicardium^ Lithocardiiim, Serripes, Adacna^ 

 Conocardium. 



Family Lucinidce. 



Mantle usually widely open below, with one or two siphonal aper- 

 tures ; foot long, cylindrical, or ligulate, sometimes byssiferous. Shell 

 orbicular, closed; hinge-teeth 1 or 2, lateral teeth 1-1, or obsolete. 



Genera Lucina^ Cryptodon, Corbis, Ungulina, Kellia, Montacuta, 

 Lepton, Galeomma. 



Family Cycladidm. 



Mantle open in front; siphons more or less united; foot large, 

 tongue-shaped. Shell suborbicular, closed ; hinge with cardinal and 

 lateral teeth. 



Genera Cyclas, Cyrena, Pisidium. 



Family Cyprinidce. 



Mantle-lobes united behind by a curtain pierced with two siphonal 

 orifices ; foot thick or compressed, tongue-shaped. Shell equivalve, 

 closed ; cardinal teeth 1-3, and usually a lateral tooth in each valve. 



Genera Cyprina, Ciree^ Astarte, Crassdtella, Isocardia, Cypri- 

 cardia, Megalodon, Cardinia, Cardita. 



b. Siphons long ; pallial line sinuated. 



Family VeneridtB. 



Mantle with a rather large anterior opening ; siphons unequal, 

 more or less united ; foot tongue-shaped, compressed, sometimes 

 grooved and byssiferous. Shell regular, closed ; hinge with usually 

 three diverging teeth in each valve. 



Genera Venus^ Cytherea, Artemis^ Lucinopsis, Venerupis, Petri- 

 cola, Glaucomya. 



Family Mactridce. 



Mantle more or less open in front ; siphons united with fringed 

 orifices ; foot compressed. Shell equivalve, trigonal ; hinge with two 

 diverging cardinal teeth, and usually with lateral teeth. 



Genera Mactra, Gnathodon^ Lutraria, Anatinella. 



Family TellinidcB. 

 Mantle widely open in front ; foot tongue-shaped, compressed ; 

 siphons separate, long and slender. Shell usually equivalve and 



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