462 PERCY SLADEN TRUST EXPEDITION 



Fig. 20. Transverse section through the base of a branch of Sporadotrema, showing a single circle of 



chambers with very thick and continuous outer walls perforated by foramina (/). Within the circle 



of chambers there is a core of calcium carbonate perforated by interlocular passages (i). x 6 



diameters. Compare this drawing with the photographs on Plate 31, figs. 14 and 17. 

 Fig. 21. Surface view of a portion of a stem of Sporadotrema, showing the irregular arrangement of the 



foramina (cc). x 50 diameters. 

 Fig. 22. Surface view of a portion of a Homotrema, showing the areolae (A) perforated by foramina and 



bounded by solid walls, x 50 diameters. 

 Fig. 23. Surface view of a portion of a Polytrema, showing the pillar pores (P) and the foramina 



perforating all the other parts of the surface (/). x 50 diameters. 

 Fig. 24. Drawing of a growing point of a specimen of Sporadotrema cylindricum, fac. Amirantiae, 



showing the young chambers (cc) at the edge with a cock's comb row of short tubes (T) opening 



freely on the distal margin, x circa 9 diameters. Compare this drawing with the photographs on 



Plate 31, figs. 15 and 16. 

 Fig. 25. Vertical section through a lamina of Sporadotrema mesentericum to show the tabula? in the 



foramina (/). These tabulae are probably never quite complete but perforated in the centre by 



a pore (compare fig. 33). x 20 diameters. 

 Fig. 26. Transverse section of a part of a branch of Sporadotrema to show the relation of the foramina 



to the chambers (c, c). x circa 18 diameters. 

 Fig. 27. Transverse section of a part of a branch of Polytrema to show the relation of the pillar pores 



(P) to the chambers (c) and the interlocular spaces (i). x circa 200 diameters. 



Fig. 28. Transverse section of a part of a branch of Homotrema to show the perforated outer walls 

 of the external chambers and the passages which establish communication between the chambers, 

 x circa 200 diameters. 



Fig. 29. Vertical section through the base of the stem of Sporadotrema cylindricum, fac. Amirantiae, 

 showing three of the initial chambers (i.c). These chambers can be recognised by their regular oval 

 shape and by the foramina which perforate their walls. Camera drawing x 10 diameters. 



Fig. 30. Chitinous tubes lining the foramina of Carpenteria raphidodendron. Copied from Mobius (13). 

 Plate VI, fig. 3. x 150 diameters. 



Fig. 31. Chitinous tubes lining the foramina of Polytrema miniaceum. Copied from Merkel (12). 



x 580 diameters. 

 Fig. 32. Chitinous tubes lining the foramina of Sporadotrema. x 150 diameters. 



Fig. 33. One of the joints in a foramen of Sporadotrema, very much enlarged, to show the narrow 

 shelf-like tabula. 



