CLASS I 



PELECYPODA 



475 



Family 7. Sphaeriidae Dall. 



Shell as in the Gyrenidae, but small, with a feeble, short ligament, a simple fallial 

 line, and no hinge plate ; cardinal teeth usually two i^i each valve, variable, very thin, 

 often nearly parallel to the hinge margin or defective in part of the series ; laterals as in 

 the Gyrenidae, distinct. Upper Cretaceous to Eecent. 



Sphaerium Scop. {Gyclas Lam., non Brug.). Branchial siphon complete ; shell 

 equilateral, inflated, rounded. Upper Cretaceous to Recent. 



Subgenus EujJera Bgt. Shell compressed, trapezoid. Tertiary and Recent ; sub-tro])ical. 



Gorncocyclas Ferussac {Pisiditim Pfeilf.). i Shell inequilateral ; branchial siphon 

 merged with the pedal opening. Eocene to Recent. 



Superfamily 4. CAEDITACEA Menke. 



This group appears to have branched off from the Astartoid radical in the early 

 Mesozoic, forming in one sense a sort of parallel series loitli the Astartidae, with tvhich it 

 is contrasted most obviously by its prevailing radial sculpture and prolonged posterior 

 cardinal tooth. 



Family 8. Oarditidae Gill. 



Shell as in the Astartidae, but usually with radial scihlpture, the pedal adjacent to 

 the anterior adductor scar ; ligament external, parivincular ; resilium usually included 

 in the ligament, rarely , internal ; hinge fidly developed, with the Icominae as in the 

 Astartidae, and usually obsolete ; the anterior cardinal often obsolete, the posterior pro- 

 longed parallel with the dorsal margin even beloiv the ligament. Full cardinal formula 



p • M&rine ; dioecious, frequently viviparous. Trias to Recent. 



The earlier forms approach the Astartidae and Pleurophoridae so closely that they can 

 hardly be discriminated. 



Gardita Brug. Elongate, quadrate, with prominent, very anterior beaks ; sculji- 



Pio. 763. 



Palaeocardita cre.nnta 

 (Munst.). Upper 

 Trias ; St. Cassian, 

 Tyrol. 



Fic. 704. 

 Venericardia imhricata Lam. Eocene ; Grignon, near Paris. 



ture radial and usually imbricated, commonly with a lunule ; inner margins dentate ; 

 cardinals long and oblique. Trias to Recent. 



Palaeocardita Conr. (Fig. 763). Like Carditct, but with a posterior lateial 

 tooth. Trias and Cretaceous. 



Venericardia Lam. (Fig. 764). Rounded or cordate ; lateral teeth al)sent or 

 obsolete. Cretaceous to Recent. 



