492 



MOLLUSCA 



PHYLUM VI 



The hinge characters of the less specialised forms hardly differ from the Diogenodonta, 

 but they are grouped here on account of their ohvious aßnities, as shown hy other 

 characters. 



Superfamily 12. VENERACEA Menke. 



Teleodonts with normal gills united to form a complete anal Chamber, the mantle 

 lobes free behind the siphonal region, sub-equal adductors, an external parivincular liga- 

 ment seated in a groove, and the shell substance densely cellulo-cry stalline with incon- 



spicuous epidermis. Complete hinge formula r^wr — —f. — q-.^-./-. 0^, of which a large 



part is usually deßcient. 



Family 31. Veneridae Leach. 



Valves equal, free, closed, with prosogyrous beaks, variably sculptured, with the 

 margins more or less dentate, except in the smooth species ; adductor scars peripheral, 

 pedal distant ; pallial sinus more or less sinuated, area very distinct ; resilium usually 

 external, embraced by the ligament ; hinge-plate developed ; formula of the cardinals 



KÖToToT' '^'^^^ ^ Single obsolete lateral in one valve ; the cardinals frequently bifid, 

 usually radially 



and sub-equal in size, except the posterior left one, which is often 

 obsolete or obscure ; supplementary cardinals or 

 rugosities are present in specialised forms. Jura 

 to Recent ; maxinuim in Tertiary and later. 



The faniily must be divided into at least four 

 subfamilies, as follows : — 



a. Venerinae : typical, with produced siphons, 

 not byssiferous, the yoimg not retained within the 

 mather after leaving the egg. 



h. Circinae : with separate short siplions, cor- 

 relative nearly simple pallial line, sub - internal, 

 partially amphidetie resilium, and compressed beaks. 



c. Tapetinae : with long but partly separated 

 siphons, a byssus present at least in the young ; 

 hinge with no lateral teeth, otherwise like the 

 Venerinae. 



d. Gemminae : minute Shells, with more or less 

 separated siphons, no byssus, obsolete lateral laminae, 

 and sheltering the nepionic young within the cavity 

 of the mother. 



a. Pronoella Fisch. (Pronoe Ag., non Guer. 



Men.). Compressed, pallial sinus very shallow ; 



a posterior lateral and tliree cardinals in eacli 



valve. Jura. 



Like the preceding, but the riglit valve wdth only 



two cardinals, the hinder one bifid ; pallial sinus very shallow. Cretaceous. 



Dosinia Scop. {Artemis auct.). Orbicular, lentiform, concentrically sculptured, 

 with a deep, well-marked lunule : cardinals 3:3; pallial sinus deep, ascending, 

 pointed. Cretaceous to Recent. 



Eocyclina Dali. (Cyclina Desh.). Cretaceous to Recent. Sunetta Link {Meroe 

 Sclium.) ; Grateloupia Desm. Tertiary and Recent. dementia Gray. Oligocene to 

 Recent. 



Venus Linn. (Fig. 808). Oval or rounded, plump, cordate, thick ; concentrically 

 or radially sculptured, with denticulate margins ; hinge-plate broad, with tliree 

 cardinals in each valve and no lateral teeth ; pallial sinus short, angular. Jura to 



Fig. 807. 

 Cyprimeria discus (Math.). Upper 

 Cretaceous ; Gosau Valley, Austria. 



Cyprimeria Conr. (Fig. 807). 



