474 Mr. D. W. Devanesen. Development of the Calcareous 



■v P 



2. 



3. 



4. 



,B.L. 



14. 15- 16 ' 



Text-Fig. 1. — Diagrammatic representation of the formation of a cone from a pair of 

 calcareous particles. 1. A. pair of calcareous particles. 2, 3, 4, 5, 6, and 7. Pro- 

 gressive stages in the formation of a pair of lamellae ; B.L., Basal end of a lamella 

 where growth takes place by accretion. 8. The pair of lamellae has attained its 

 maximum vertical growth, further increase taking place only at the lateral edges ; 

 the two lamelliC are undergoing slight bending due probably to the pressure of 

 lamellse subsequently deposited. 9 and 10. The inner lateral edges of the two 

 lamella; have commenced to grow ; A., The first spot where the latter come into 

 contact and fuse. 11 and 12. The inner lateral edges have approximated and are 

 gradually fusing ; the outer lateral edges have also begun to join ; it will be 

 noticed that both the commencement and the completion of the fusion of these 

 latter edges are later than those of the inner : this stage in the formation of a 

 cone may be called the " incipient cone " stage. 13. The flange F., at the top corner 

 of each inner lateral edge, has appeared. 14. The same flanges have joined, 

 forming the characteristic beak. 15. A complete cone ; BK., Beak. 16. Two 

 cones showing their relation to each other ; P.P., the spot where the fusion 

 between the apices of the two cones takes place, this being the foundation for the 

 formation of an axial rod — the " pars petrosa." 



The relative position of the two fellow lamellae of a pair deserves notice. 

 They are deposited in close proximity to each other, but do not touch, and 

 also at different levels so that they alternate. As growth proceeds, however, 



