CLA.SS I 



PELECYPODA 

 Family 27. Megalodontidae Zittcl.' 



453 



> Shells equivalve, sah-mytüiform, closed, witli feehle concentric sculpture or none ; di- 



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

 hy nijmphae; cardinal teeth strong, usually two or three, ivith a posterior lateral, all 



Fig. 696. 

 MigiiJniliiii (Eumcijalodon) cucullatus Goldf. 

 near Cologne. i/^. 



Devonian ; Pattrath, 



tri'iurti i{\\'uUtiu). lutenial 

 niould. Trias dolomite ; 

 Bleiberg, Carinthia. 



Fio. 698. 

 Megalodon (Neomeij'ilniltiii) fiilmheli Stoppani. Rhaetic ; Elbigenalp, Tyrol (after Gümbel). 



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

 ridfje and pedal scar, the posterior adductor scars frequently hordered hy an elevated 

 crest. Marine. Silurian to Upper Jura. 



These Shells, which are ofteii 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 

 üxed as yet. Pachyrisma is thought by Böhm to be genetically related to Cardium, and the 

 genus Mcgalodon niay have been ancestral to primitive Chamacea. 



Megalodon Sow. {Tauroceras amd Lycodes Schafli. ; Conchodon Stopp.) (Figs. 696-698). 



^ Gümhel, C. W., Die Dachsteinbivalven. Sitzuiigsber. Akad. Wiss. Wien, 1862, vol. xlv. — 

 ITocnu's, R., Materialen zu einer Monographie der Gattung Megalodus. Denkschr. Akad. Wiss. 

 Wien, 1880, vol. xl. — Böhm, G. Megalodon, Pachyrisma und Diceras. JSer. Naturforsch. 

 Gesellsch. Freiburg, 1891, vol. vi. 



