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Alasmodonta. Lateral teeth none; cardinal teeth simple, or slightly 

 divided. 



A. margaritifera, (Unio sinuata of Lnm'k.) A. rugosa, (Barnes.) S. J. vol. 6, pi. xiii. f. 21- 



Wood's Gen. Cone. pi. xxii. f. 1. 23. ' maro-inata, (Say.) 



' arcuata, (Barnes.) Sil. Jour. vol. 6, pi. xii. ' undulata, see Say's desc. and fig - , in A. C. 



f. 20. — old and young. ' confragrosus, (Say.) Am. Cone. pi. xxi. 



Symphynota. Shell fluviatile, bivalve; valves connate at the dorsal margin. 



S. Isevissima, (Lea.) T. A. P. S. pi. xiii. f. 23. S. gracilis, (Barnes.) Sil. Jour. vol. 6. 



' bialata, do. pi. xix. f. 24. ' tenuissima, (Lea.) T. A. P. S. pi. xi. f. 21. 



' alata, (Lara'k.) Barnes, in S. J. vol. 6. ' bilineata, (Lea.) Trans. Am. Phil. Soc. 



' complanata, do. do. page 278. — rare. vol. 4, pi. xi. f. 19. 



' compressa, (Lea.) T. A. P. S. pi. xii. f. 22. « inflata, do. do. pi. xiv. f. 28. 



CHAMACEA.— Three Genera. 



Shell inequivalve, irregular, fixed; hinge with one thick tooth, or without 

 teeth; two separate lateral muscular impressions. 



Diceras. Shell inequivalve, adhering; the beaks conical, very large, 

 diverging, irregularly spiral; one large, thick, concave, subauricular, promi- 

 nent tooth in the greater valve; two muscular impressions. 



1 fossil species. 



Chama. Shell irregular, inequivalve, fixed; the beaks curved and unequal; 

 hinge with one thick, oblique, subcrenate tooth, fitting in a pit in the opposite 

 valve; two distant, lateral, muscular impressions. Ligament external, sunk. 



C. lazarus, C. florida, C. arcinella, C. ruderalis, 



' damEecornis, ' limbula, ' radians, ' croceata, 



' gryphoides, ' aeruginosa, ' cristella, ' Japonica, 



' crenulata, ' asperella, ' albida, 8 fossil species. 



' unicornis, ' decussata, 



Etheria. Shell irregular, inequivalve, fixed; the beaks short, almost 

 sunk in the base of the valves; hinge without teeth, rather sinuous, unequal; 

 two distant, lateral, oblong, muscular impressions. Ligament external, tor- 

 tuous, partly penetrating the shell. 



E. elliptica, E. semilunata, E. transversa, E. Carteronii. 



' trigonula, 



