38 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 2, 



ginal chambers ; a, a, a, c, shell-wall of portions of the four chambers sepa- 

 rated by the septa 5, h, b, perforated by minute orifices, which are those 

 of the parallel vertical tubuli shown in fig. 15, and traversed iitegularly 

 by canals, c, c, which open into the chambers by distinct orifices, d, d, 

 and terminate in the intraseptal spaces. Magnified 60 diam. 



Fig. 17. Transparent section of Nummulina complanata, in a direction vertical to 

 the median plane, showing the several investing layers in close appo- 

 sition with each other, and not separated by prolongations of the mar- 

 ginal chambers. Magnified 6 diam. 



Fig. 18. Transparent section of Orbitoides (undescribed species), in a direction 

 vertical to the median plane, presenting, in the size of its chambered 

 layer, a close resemblance to the Nummulitic structure. Magnified 20 

 diam. 



Fig. 19. Vertical section of Orbitoides (undescribed species from Scinde), with a 

 very thin chambered layer, a, a, and the vertical channels (filled with 

 opake infiltration) of unusual size. Magnified 9 diam. 



Fig. 20. Vertical section of Orbitoides Mantelli, showing the chambered layer, 



a, a, occupying the median plane, and the investing layers, b, b, above 

 and below. Alagnified 60 diam. 



Fig. 21. Section of Orbitoides Mantelli through the median plane, showing the 

 form of the cells of the chambered layer, partly filled by calcareous infil- 

 tration. Magnified 60 diam. 



Fig. 22. Section of Orbitoides (undescribed species from Biaritz) in a direction 

 vertical to the median plane. Magnified 30 diam. 



Fig. 23. Section of Orbitolites complanata through the median plane. Magnified 

 60 diam. 



Fig. 24. Section of Marginopora {Orbitolites, recent Australian species, unde- 

 scribed) through the median plane, but passing through the more super- 

 ficial portion near the margin, at a, a, a. Magnified 10 diam. 



Fig. 25. Portion of the same, taken near a, a, and showing the form of the cells 

 near the surface. Magnified 60 diam. 



Fig. 26. Portion of the same, taken near the centre, and showing the form of the 

 cells nearer the median plane. Magnified 60 diam. 



Fig. 27. Vertical section of the same, showing the single layer, a, a, of superficial 

 chambers on each surface, and the structure of the intervening portion, 



b, b, of the disk. Magnified 60 diam. 



Fig. 28. Thin slice from the edge of the disk, showing the pores opening on its 

 margin. Magnified 90 diam. 



Fig. 29. Portion of the surface of the same, viewed as an opake object, showing 

 the superficial chambers, some of them closed in, others laid open by 

 the abrasion of their covering. Magnified 60 diam. 



Fig. 30. Portion of the surface of Orbitolites complanata, viewed as an opake ob^ 

 ject, showing the superficial chambers, closed in at the lower part of the 

 figure, laid open by abrasion at the upper part. Magnified 60 diam. 



Fig. 31. Portion of the surface of the chambered layer of Orbitoides Mantelli, 

 showing the chambers covered in and a few laid open. The investing 

 layers have here been removed. Magnified 30 diam. 



Fig. 32. Transparent section of Orbitoides Prattii, passing through the median 

 plane ; a, a, the investing layers ; b, portions of the median chambered 

 layer, showing at ¥ a very irregular arrangement of the chambers. Mag- 

 nified 12 diam. 



Fig. 33. Portion of fig. 32, a, more highly magnified, showing the form of the ceUs 

 of the investing layers, and the perforation of the shelly substance by 

 minute tubuli. Magnified 60 diam. 



Fig. 34. Portion of fig. 32, J, more highly magnified, showing the form of the cells 

 of the chambered layer. Magnified 60 diam. 



Fig. 35. Vertical section of the entire disk of Orbitoides Prattii, showing the 

 median chambered layer, and the investing layers above and below ; 

 at a is seen the large globular cell in which the chambers of Foramini- 

 fera always seem to commence. Magnified 10 diam. 



Fig. 36. Portion of the same section more enlarged, showing the chambered layer. 



