158 



On the Class ificalton of the Pelecypoda 



however, as set forth by the author will hardly commend it 

 to practical malacologists. 



Pelseneer's scheme appears so decidedly in advance of the 

 others that after consultation with my friend and colleague 

 Mr. E. A. Smith it has been decided to adopt it in future 

 volumes of the ' Zoological Record/ retaining Fischer's 

 families as far as possible for the present for the sake of 

 convenience in reference. 



Since, however, the ' Zoological Record ' does not admit of 

 the new arrangement being shown in its entirety, it seems 

 fairer that it should in the first instance be published where 

 it will be available to all in a handy form. 



Hitherto only the relationship of the main groups has been 

 published, and that in a " tree " which should be studied in 

 conjunction with the linear arrangement that here follows ; 

 for in the latter of course the essential features of the " tree " 

 cannot be reproduced, though some help is sought to be given 

 by " indenting " those families which lie on the divergent 

 branches and placing them between '* rules," after the method 

 familiar in a railway time-table. 



The three families not in Fischer are printed in italics. 



Class PELECYPODA. 



Order I. SEPTIBRANCHIATA. 



Fani. 1. Poromyida; {Poromya and 

 Silenia). 

 2. Cuspidariidae. 



Order II. EULAMELLIBRAN- 

 CHIATA. 



Subord. i. Anatinacka. 



Fam. 3. Clavigellidfe. 



4. Pholadomyidee. 



5, PraecardiidPB. 

 0. Grammysiidfe. 



7. Anatinidaj (excepting 



Poromya). 



8. Arcomyidfe. 



9. Ceromyidse. 



10. Lyonsiidae (excepting 



Silenia) . 



11. Verticordiidfe. 



12. Chamostreidfe. 

 l.'l Pandoridse. 



Subord. ii. Pholadacea. 



Fam. 14. Teredin'dse. 

 15. Pholadida>. 

 10. Gastroclia3uid{». 



Subord. iii. Myacea. 



Fam. 17. Solenidse. 



18. Glycymerida3. 



19. Myidfe. 



20. Lutrariidce. 



Subord. iv. Cardiacea. 



Fam. 21. Radiolitidae. 



22. Hippuritidpe. 



23. Caprinidse. 



24. Monopleuridte. 



25. Cliamidfe. 



26. Tridacnidje. 



27. Lunulicardiid;e. 



28. Cardiid*. 



Subord. V. Veneracea. 



Fam. 29, Psammobiidse. 



30. Cyrenellidaj. 



31. Rangiidse. 



32. Cyrenidse. 



33. Glaucomyidae. 



34. Petri colidse. 



35. Veneridse. 



36. Pachydomida;. 



37. Cyprinidae. 



38. Megalodontidas. 



