46 PERCY SLADEN TRUST EXPEDITION 
The walls and foramina are of about the same size in the other specimens, but the 
chambers as above stated are smaller, those from Providence varying between 80 and 
150», with an average of 105» and from Amirante 49—115 p with an average of 89 p. 

Fig. 1. Specimen of Gypsina plana, Carter, from 100—200 fathoms, oft Mauritius, nat. size. 
A vertical section through the incrustation shows the chambers arranged in rows 
parallel to the surface, the chambers of one row alternating more or less regularly with 
those of the row above. 
The typical form of the chambers as seen in such a section is more or less oblong, the 
upper and lower walls being slightly convex outwards; the surface walls do not differ 
from the others in any noticeable features, though on the whole they are somewhat flatter. 
The chambers are seen communicating with one another by gaps in the wall 
representing the foramina. 

Fig. 2. Vertical section, magnified about 120 diameters. 
On account of the presence of the irregular projections of more or less spherical 
nature, such a true vertical section is rather difficult to obtain, and the most usual one 
is a transverse section through one of these knobs. 
In such a transverse section the cells are seen more or less concentrically arranged 
round a common centre, especially in the outer layers, the inner ones being frequently 
