412 



MOLLUSCA 

 Family 26. Cardiidae. Fischer. 



SUB-KINGDOM VI 



Shell substance cellulo-crystalline, ivith the external layer more or less tubular ; valves 

 equal, free, gaping slightly behind, the beaks prosocoelous, the margins usually serrate or 

 radially striated; adductor scars sub-equal, the pedal distinct and usually distant; 

 ligament and resilium parivincular, external, short, set in a groove ; area obscure ; com- 

 plete hinge armature consisting of an anterior and posterior lateral in the left, and two 





FIG. 752. 

 Cardiiim productum, Sow. Turonian ; St. Gilgen, Salzburg, 1/1- 



anterior and one posterior lateral in the right valve, any or all of which may be absent ; 

 cardinal formula ^ 101Q , the teeth simple, smooth, never bifid, one cardinal in each valve 

 usually persistent, the others inconstant. Trias to Recent. 



Cardium, Linn. (Figs. 752-754). Cordate, inflated, radiately ribbed or striated, 



FIG. 753. 



Protocardia bifrons, 

 Reuss. Turonian; 

 Strobl-Weissenbach am 

 Wolfgangsee, Austria. 



Vi- 



Cardium (Discors) discrep'ans, Bast. 

 Bordeaux, 1/1- 



Miocene ; Dax, near 



with prominent beaks. Represented by about 200 recent and over 100 fossil species. 

 Trias to Recent. 



A very large number of sub-genera and sections have been proposed, based chiefly on the 

 external sculpture. Some of the more conspicuous groups are the following : 



Protocardia, Beyr. (Fig. 753). Cretaceous. Discors, Desh. (Fig. 754) ; Lacvicardium, 

 Swains. ; Serripes, Beck ; Hemicardium, Cuvier ; Papyridca, Swains. Tertiary and Recent. 

 Didacna, Eichwald, estuarine, leads toward the next family. 



