ILLUSTRATIONS 



PLATES Exp™ 



Page 



1. Atribonium 175 



2. Atribonium 175 



3. Atribonium 176 



4. Sedenticellula, Septacamera, Camarophorinella 176 



5. Sedenticellula 177 



6. Cyrolexis 177 



7. Cyclothyris, Camarophorina 177 



8. Camerisma 178 



9. Psilocamara, Coledium 178 



10. Coledium 179 



11. Coledium 179 



12. Coledium 179 



13. Coledium 180 



14. Coledium 180 



15. Coledium 180 



16. Coledium 181 



17. Coledium 181 



18. Coledium 182 



19. Stenoscisma 182 



20. Stenoscisma 183 



21. Stenoscisma 183 



22. Stenoscisma 183 



23. Stenoscisma 184 



24. Torynechus 184 



FIGURES 



Page 



1. Reconstruction of arrangement of principal muscles in Stenoscisma- 

 tacea, based on Stenoscisma 19 



2. Interior of pedicle valve of Stenoscisma 24 



3. Phylogeny of the Stenoscismatacea 30 



4. Longitudinal section of Atribonium simatum 42 



5. Serial sections of Atribonium simatum 42 



6. Scatter diagram of Atribonium simattim 44 



7. Serial sections of Atribonium cooper orum 46 



8. Serial sections of Atribonium gregeri 49 



9. Scatter diagram of A tribonium gregeri 50 



10. Scatter diagram of Atribonium pinque 59 



11. Serial sections of Camerisma prava 67 



12. Serial sections of Camerisma girtyi 68 



13. Serial sections of Camerisma sagmaria 70 



14. Serial sections of Sedenticellula hamburgensis 74 



15. Serial sections of Psilocamara renfroarum 80 



16. Serial sections of Camarophorina antisella 84 



iv 



