398 MOLLUSCA SUB-KINGDOM VI 
Family 7. Sphaeriidae. Dall. 
Shell as in the Cyrenidae, but small, with a feeble, short ligament, a simple pallial 
line, and no hinge plate; cardinal teeth usually two in each valve, variable, very thin, 
often nearly parallel to the hinge margin or defective in part of the series ; laterals as in 
the Cyrenidae, distinct. Upper Cretaceous to Recent. 
Sphaertum, Scop. (Cyclas, Brug.) | Branchial siphon complete; shell inflated, 
rounded. Upper Cretaceous to Recent. 
Sub-genus Lupera, Bgt. Shell compressed, trapezoid. Tertiary and Recent ; sub-tropical. 
Pisidium, Ptr. Shell inequilateral; branchial siphon merged with the pedal 
opening. Eocene to Recent. 
Superfamily 4. CARDITACEA. 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 with the Astartidae, with which it 
is contrasted most obviously by its prevaclingly radial sculpture and prolonged posterior 
cardinal tooth. 
Family 8. Carditidae. Gill. 
Shell as in the Astartidae, but usually with radial sculpture, the pedal adjacent to 
the anterior adductor scar ; ligament external, parivincular ; resilium usually tneluded 
in the ligament, rarely internal; hinge fully developed, with the laminae as in the 
Astartidae, and usually obsolete ; the anterior cardinal often obsolete, the posterior pro- 
longed parallel with the dorsal margin even below the ligament. Full cardinal formula 
L01010 
R10101 
The earlier forms approach the Astartidae and Pleurophoridae so closely that they ean 
hardly be discriminated. 
Marine. ‘Trias to Recent. 
Cardita, Brug. Elongate, quadrate, with prominent, very anterior beaks ; seulp- 

Fic. 714. 
Palacocardita crenata, 

Miinst. sp. Upper Fic. 715 
Trias; St. Cassian, nn ae 
Tyrol. Venericardia imbricata, 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, Cony. (Fig. 714). Like Cardita, but with a posterior lateral 
tooth. Trias and Cretaceous. 
Venericardia, Lam. (Fig. 715). Rounded or cordate; lateral teeth absent or 
obsolete. Cretaceous to Recent. 
