SPIBJFER MUCRONATUS VAR. THEDEORDENSIS S. AND G. 



175 





Ephebic. 



Neanic. 





Nepionic. 











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3 



£ 



% 



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p 



5 



% 



'53 



w 



o 



5 



30 



28. 



19.6 



1.43 



10 



22.4 



10.4 



2.2 



9 



13. 



6.1 



2.1 



8 



31 



34.8 



17.3 



2. 



12 



32. 



9. 



3.5 



10 



7.4 



3.7 



2. 



7 



32 



37.8 



20.5 



1.8 



13 



33.2 



9.2 



3.6 



9 



5. 



2.9 



1.7 



5 



33 



41.6 



22. 



1.9 



14 



39. 



9.3 



4.2 



11 



4.2 



2.8 



1.5 



7 



34 



39. 



20. 



1.95 



13 



37.2 



9.9 



3.76 



10 



10. 



5. 



2. 



8 



35 



33.4 



20.1 



1.7 



12 



28.8 



7.7 



3.8 



10 



6.4 



3.9 



1.6 



6 



36 



32.6 



17.6 



1.9 



10 



18. 



6.6 



2.7 



8 



6.4 



4. 



1.6 



5 



37 



40.4 



20.8 



1.9 



12 



39. 



9.4 



4.1 



9 



10. 



4.4 



2.3 



7 



38 



41.8 



17.8 



2.4 



16 



36.4 



9.5 



3.8 



10 



5.6 



3.4 



1.6 



7 



39 



35.6 



18.9 



1.9 



10 



34. 



12.1 



2.8 



11 



6.4 



3.3 



1.9 



7 



40 



34. 



16.8 



2. 



11 



31. 



7.8 



3.9 



11 



6.6 



3.6 



1.8 



5 



41 



37.8 



14. 



2.7 



14 



35.8 



9.6 



3.7 



12 



7.6 



3.3 



2.3 



6 



42 



32.6 



17.7 



1.8 



11 



28.4 



7.3 



3.8 



9 



6.6 



3.9 



1.7 



7 



43 



32. 



18.6 



1.7 



11 



26.2 



10.5 



2.5 



9 



7. 



4.1 



1.7 



7 



44 



26.6 



16.4 



1.6 



12 



21. 



6.2 



3.4 



10 



5.6 



3.8 



1.5 



5 



45 



34.8 



17.4 



2. 



12 



30.4 



8.9 



3.4 



12 



5.6 



3.7 



1.5 



6 



46 



36.2 



20. 



1.8 



13 



31.2 



8.8 



3.5 



13 



7. 



3.5 



2. 



7 



47 



36.8 



19. 



1.9 



11 



32.6 



12.7 



2.6 



11 



6. 



3.5 



1.7 



7 



48 



37. 



20. 



1.8 



13 



32.4 



6.9 



4.7 



11 



7. 



3.5 



2. 



6 



49 



38. 



17.2 



2.2 



15 



32. 



9.5 



3.4 



10 



12. 



6.1 



2. 



9 



50 



41.2 



19.3 



2.1 



12 



39.2 



10. 



3.9 



11 



6.8 



3.6 



1.9 



6 



51 



38.2 



20.3 



1.9 



12 



33.4 



8.9 



3.8 



11 



5.6 



3.2 



1.8 



6 



52 



32.6 



19.2 



1.7 



11 



28. 



6.9 



4. 



11 



5. 



3.1 



1.6 



5 



53 



29.4 



19.2 



1.5 



11 



27. 



7.5 



3.6 



11 



8. 



4. 



2. 



7 



54 



35. 



20. 



1.8 



11 



33.6 



8.8 



3.8 



10 



7.4 



3.8 



1.9 



8 



55 



30. 



19.8 



1.5 



14 



27.8 



9.5 



2.9 



9 



7.8 



4.7 



1.7 



6 



56 



26.4 



19.2 



1.4 



9 



21.6 



10.6 



2. 



8 



8. 



4.5 



1.8 



6 



57 



42. 



21. 



2. 



13 



39.2 



8.2 



4.7 



7 



5.8 



4. 



1.5 



7 



58 



36.4 



19.8 



1.8 



15 



33. 



9.6 



3.4 



14 



7. 



3.5 



2. 



7 



59 



41. 



18.5 



2.2 



13 



39. 



10.8 



3.6 



13 



9.4 



4.8 



1.8 



6 



This variety is already well developed in the coral layer, where char- 

 acteristic individuals occur. In this horizon the variation is perhaps 

 somewhat greater than in the higher ones, if our collections adequately 

 represent this feature. Along with normal individuals of variety thed- 

 fordensis occur others, which retain the primitive mucronatus character 

 for a sufficiently long period to permit their being classed under that 

 species. These individuals are more elongate than the normal form of 

 the variety thedfordensis, but they never reach the extreme elongation 

 characteristic of variety arkonensis. The plicated sinus and medially 



