General Classijication of the Pelecypoda. 



97 



taxodont form. Dall noticed tlio same origin for the 

 Auisoinyariau teeth ; but he read it as excluding them 

 from any coauectiou with the Taxodoiita, whose teeth he 



Fi"-. 3. 



Young stages oi Area. (After Bernard.) 

 C = baud of crenulations; Li = primary ligauiental pit; L=;ligaineat. 



A nr 



L_^ 



Fig. 4. 

 L.9 



p nr 



pn 



Avicula microptera (after Bernard^, showing the dysodont teeth, wliicli 

 anteriorly show a tendency to produce cardinals. 



conceived as arising perpendicular to the hinge-line. Con- 

 firming the fact that the dysodont stage precedes tiie taxo- 

 dont, Bernard cites the case of the development of those young 

 Ann. (I; Mag. N. Hist. Ser. 8. Vol. x. 7 



