48 PERCY SLADEN TRUST EXPEDITION 
kind, there being no evidence of the so-called pillar pores of Polytrema nor any other 
large spaces or passages of any kind. 
Compared with the foramina of the Polytrema group these are of relatively large size 
(5p in this form and 1 pw in Polytrema) and relatively few in number. 
The walls are seen in thin sections to consist of fibrous crystalline calcite; each 
chamber has not its own individual wall, but is built up, so to speak, on the layer 
below (Figs. 4 and 5). 
No coiled initial chambers have been observed, but this is possibly due to the large 
size of the specimens making search very difficult, and it is more than probable that the 
mass did arise from some such coiled chambers as are found in other sedentary fora- 
minifera. Once started on its encrusting mode of life it simply enveloped everything it 
came across, as is well seen in some sections (unfortunately too thick to photograph) where 
the foraminifer is seen surrounding Polytrema. Here the chambers immediately round the 


Fig. 6. Section showing a shell of Polytrema in the centre surrounded by the chambers of Gypsina. 
Polytrema are smaller and flatter than the ordinary ones, but do not differ otherwise, and 
gradually merge into quite typical perforate chambers. 
Some of the spirit material was decalcified and sections of the remaining soft parts 
were obtaimed. These, however, were not very successful, as the material shrank 
considerably on being embedded in wax, and they showed no further details except that 
in one series there was a suggestion of an initial chamber, but this was unfortunately not 
clear enough to make a definite statement about. 
Briefly, then, the foraminifer may be described as follows: Sedentary, of large size, 
the surface marked into clearly defined areolze about 120 in diameter and with the walls 
of each chamber perforated by a few large foramina—5 p» in diameter. Below the surface 
are seen rows of chambers communicating by perforations in the walls and not by large 
open passages. There is no general aperture and no supplemental skeleton of spines and 
tubercles as in Tinoporus. 
A point worthy of notice in connection with this foraminifer is the occurrence of large 
