CLASS I 



PELECYPODA 



453 



Family 27. Megalodontidae Zittcl.^ 



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

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

 by nympha^e ; cardinal teeth strong, usually tivo or three, with a posterior lateral, all 



Pio. 696. 

 Megalodon (Ewinegalodon) cncullatus Goldf. 

 near Cologne, i/j. 



Devonian ; Paft'rath, 



Pig. 69T. 

 Megalodon(Neomegalodon) 

 triqurU'r (Wulfeii). Internal 

 mould. Trias dolomite ; 

 Bleiberg, Carinthia. 



Fk.;. G9S. 

 Megalodon (Neomegalodon) griimfteHiStoppani.'^Rhaetic Blbigenalp, Tyrol (after Giimbel). 



heavy and amorphous ; anterior adductor scars distinct, loith a well-marhed myophoric 

 ridge and pedal scar, the posterior adductor scars frequently bordered by an elevated 

 crest. Marine. Silurian to Upper Jura. 



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. Pachyrisma is thought by Bohm to be genetically related to Cardium, and the 

 genus Megalodon may have been ancestral to primitive Chamacea. 



Megalodon Sow. (TcMiroceras and Lycodes Schafli. ; Conchodon Stopp.) (Figs. 696-698). 



1 Gllmbel, C. W., Die Daehstelnbivalveu. Sitzungsber. Akad. Wiss. Wien, 1862, vol. xlv. — 

 Hoernes, ii., Materialen zu einer Monographic der Gattung Megalodns. Denkschr. Akad. Wiss. 

 Wien, 1880, vol. xl. — Buhm, O. Megalodon, Pachyrisma und Diceras. Ber. Natiirforsch. 

 Gesellsch. Freiburg, 1891, vol. vi. 



