128 



EXPLANATION OF PLATE XVII. 



Fig. 1. Horizontal section of Amphistegina gibbosa ; magnified 76 diameters. P. 106. 



2. Vertical section of the same, made through the centre of the object. 



3. Small portion of the external margin of a horizontal section of Amphistegina 



Antillarum ; magnified 170 diameters. P. 111. 



4. Vertical section of a Nonionina from the Philippine Islands ; magnified 45 



diameters. P. 112. 



5. Vertical section of a small portion of the same species ; magnified 160 dia- 



meters. 



6. Horizontal section of portions of two convolutions of the same species ; mag- 



nified 54 diameters. 



7. Horizontal section of part of the external parietes, viewed by transmitted 



light as a transparent object, and showing the translucent, supraseptal 

 spaces (a). 



8. Vertical section of Orbiculina (Orbitolites) complanata from the Philippine 



Islands ; magnified 70 diameters. P. 115. 



EXPLANATION OF PLATE XVIII. 



Fig. 9. Portion of the same section, still more highly magnified. 



10. Horizontal section of the same species, showing the primordial cell and some 



of the early additional growths; magnified 100 diameters. P. 115. 



11. Vertical section of an undescribed species of Orbiculina from Tonga 



(Friendly Islands) ; magnified 20 diameters. P. 117. 



12. Portion of the same section ; magnified 100 diameters. 



13. External surface of a portion of the same, showing the superficial fossae. 



The part to the right hand (b) of the figure is in its normal state. On the 

 opposite side (a) the surface is slightly ground down, in order to reveal the 

 conformation of the base of each fossa. Magnified 140 diameters. 



14. Horizontal section of the central primordial cell of the same species, with its 



early additional growths ; magnified 60 diameters. P. 119. 



15. Young state of Orbiculina adunca, viewed by reflected light ; magnified 20 



diameters. P. 120. 



16. Similar representation of a matured individual of the same species from 



Cuba ; magnified 20 diameters. P. 121. 



17. Vertical section of a portion of the same species, made along the line b (fig. 



16) ; magnified 160 diameters. P. 121. 



18. Superficial horizontal section of the same portion, viewed from within ; mag- 



nified 170 diameters. P. 122. 



19. Vertical section of one umbilical region of Polystomella crispa, viewed by 



transmitted light, as a transparent object. Its inferior border descends a 

 little lower than the median plane of the organism. Magnified 100 dia- 

 meters. P. 123. 



