w 
376 MOLLUSCA SUB-KINGDOM VI 
5 Fe bs 
Family 27. Megalodontidae. Zittel. 
Shells equivalve, sub-Mytiliform, closed, with feeble concentric sculpture or none; di- 
myarian, with amphidetic area, and external opisthodetic ligament, frequently supported 
hy nymphae; cardinal teeth strong, usually two or three, with a posterior lateral, all 
heavy and amorphous ; anterior adductor scars distinct, with a well-marked myophoriec 
ridge and pedal scar, the posterior adductor scars frequently bordered by an elevated crest. 
Marine. Devonian to Cretaceous. 
These shells, which are often very ponderous, sometimes bear a remarkable resemblance 
to some recent American Uniones. The myophoric ridge is common to very distinct bivalves 
of many unrelated groups. The true position of these forms cannot be regarded as positively 
fixed as yet. 
Megalodon, Sow. (Tauroceras, Lycodes, Schath.; Conchodon, Stopp.), (Figs. 647- 

Fic. 648. 
Fic. 647. Megalodon (Neomegatodon) 
triqueter, Wulfen sp. In- 
Megalodon (Eumegalodon) cucullatus, Goldf. Devonian; Paffrath, near ternal cast. Trias dolomite ; 
Cologne. 1/3. Bleiberg, Carinthia. 
649). Beaks prosogyrous; hinge plate very broad and massive, without laterals; the 

Fic. 649. 
Megalodon (Neomegalodon) Giimbeli, Stoppani. Rhaetic ; Elbigenalp, Tyrol (after Giimbel). 
two cardinal teeth separated by a deep socket ; anterior adductor scar small, semilunar, 
