PLATE XV. 

 Okbitolites. 



Diam. Page 



Figures 1-5. — Orbitolites marginalis, Lamarck, sp., . . x 30 214 



Illustrating the various stages of growth. 



Figs. 1-4. Young specimens ; fig. 4, viewed by transmitted light. 



Fig. 5. Adult shell ; a, lateral aspect ; b, peripheral aspect. 



6, 7. — Orbitolites tenuissima, Carpenter, . . . x 20 212 



Fig. 6. a, Central portion of a disk, lateral aspect; 



b, peripheral aspect of the same, showing the 



marginal pores ; c, portion further removed from 



the centre, with less distinct septation ; </, 



another portion, the annuli of irregular width 



and not subdivided into chamberlets. 

 Fig. 7. Central portion of another specimen, viewed 



by transmitted light. 



