92 



THE OCEAN WOULD. 



nautilus shape which misled the earlier naturalists. In some cases 

 all the convolutions are visible, as in Operculina (Fig. 16). In others, 

 the external convolute conceals those previously formed, as in Num- 

 mulitis lenticularis (Fig. 17), Cassidulina (Fig. 18), Textilaria 



Fig. 14. Orbulina 

 universa. 



Fig 16. Operculina. 



Fig. 15. Dentalina 

 cornmuuis. 



Fig. 18. Cassidulina. 



Fig. 19. Textilaria. 



Fig. 17. Nummulitis 

 lenticularis. 



Fig. 20. Spiroloculina. 



(Fig. 19), and Alveolina oblonga, d'Orbigny (Fig. 25), the latter 

 forming part of the eocene formation in the quartz and greystone 

 rocks of the neighbourhood of Paris; one figure representing the 

 . shell entire, and the other a vertical section, while the small figure 

 between represents it in its natural size. 



In the fourth group the shell is spiral, with the chamber equilateral, 

 with a larger and smaller side, the position being alternately reversed 

 as the segments are multiplied, as in Cassidulina (Fig. 18). In 

 the succeeding group the new segments are arranged alternately on 

 opposite sides of the central line, as in Textilaria (Fig. 19), thus 

 forming two alternating non-spiral parallel segments, each connected 

 by a single orifice. 



