M8 Mr. H. J. Carter on the Fossil Foramiuifera of Sciade. 



ap])licd the term " central," and to the latter, " circumambient 

 cell." When the germ or central cell and its accompanying one 

 remain minute, that is, not more than the l-630th of an inch in 

 diameter, the chambers immediately around it are equally so, 

 but increase in magnitude with their distance from the centre ; 

 on the other hand, when they are large, the immediately sur- 

 rounding chambers are proportionately large, but gradually di- 

 minish to the usual size, after which they also begin to increase 

 slightly again with their distance from the centre, in the normal 

 way. Thus the structure of the centre may be compact or open, 

 but, from the open structure diminishing to a certain degree and 

 then enlarging again, it may be assumed that the former or 

 compact structure, where the chambers undergo an uninter- 

 rupted and gradual increase in size from the centre outwards, is 

 the normal form. After a certain distance from the centre, the 

 increase in size appears to cease, on account of the maximum 

 size of the chambers having been attained, when they again 

 begin to decrease in magnitude towards the circumference. 



The rows of chambers, whether arising from a minute or 

 large central cell and its accompaniment, have a tendency to a 

 cyclical arrangement from the first, and very soon complete one 

 (PI. XVII. fig. 1 in, n)j that is, they very nearly surround the 

 central chambers first for a few rows, which tend to keep on one 

 side, and then at last embrace it by completing the circle. For- 

 merly I thought they began multi-spirally, and I gave an illus- 

 tration of this (Ann. Nat. Hist. ser. 2. vol. xi. pi. 7. fig. 26) ; but 

 latterly I have found out that this illustration was taken from 

 the centre of a minute HeterostegiTm, as before stated, and that 

 Orbitoides dispansa tends to a cyclical arrangement in the centre 

 as much as, if not more than any other discoid Foraminifer. 

 As the rows extend outwards they bifurcate every now and then, 

 and every now and then one seems to stop altogether ; so that 

 this causes an increase and decrease in the number of rows 

 respectively ; but the latter is of course less than the former, 

 otherwise there would be no extension of the plane at all. This 

 irregularity, therefore, is attended by frequent interruption of 

 the circle, and thus leads to a more or less irregular aspect of 

 the rows generally throughout the plane. 



The chambers in the normal form (that is, where they com- 

 mence from a minute cell) are small and cubical in the centre 

 (PL XVI. fig. 1 h), but become elongated horizontally and com- 

 pressed vertically with their distance from it (fig. 1 // 1) ; so that 

 they soon assume a narrow quadrangular form {k i), which is 

 furthermore altered by becoming convex externally and concave 

 towards the centre, in which direction, also, their long axis is at 

 first situated ; but as the outermost rows of the full-grown test 



