376 



MOLLUSCA 



SUB-KINGDOM VI 



Family 27. Meg-alodontidae. Zittel. 



Shells equivalve, sub-Mytiliform, closed, with feeble concentric sculpture or none ; di- 

 myarian, with amphidetic area, and external opisthodetic ligament, frequently supported 

 by nymphae ; cardinal teeth strong, usually two or three, with a posterior lateral, all 

 heavy and amorphous ; anterior adductor scars distinct, with a well-marked myophoric 

 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, Ly codes, Schafh. ; Conchodon, Stopp.), (Figs. 647- 



FIG. 647. 



Mcijulodon (Eumegalodon) cmullatus, Goldf. 

 Cologne, Vi- 



Devonian ; Paffrath, near 



FIG. 048. 



Megalodon .(Neomeyalodori) 

 triqueter, Wulfen sp. In- 

 ternal cast. Trias dolomite ; 

 Bleiberg, Carinthia. 



649). Beaks prosogyrous ; hinge plate very broad and massive, without laterals ; the 



FIG. 640. 

 Megalodon (Neomegalodori) Gilmlxli, Stoppani. Rhaetic ; Elbigenalp, Tyrol (after Giimbel). 



two cardinal teeth separated by a deep socket; anterior adductor scar small, semilunar, 



