12 G. M. DAWSON ON A NEW SPECIES OF 
species, “¢ primarily of a continuous lamina coiled upon itself, like a 
scroll constricted at the ends. The space enclosed by this ‘ primary 
lamina’ is divided into chambers by longitudinal septa. The septa 
are of ‘secondary’ growth ; that is to say, they are not continuous 
with the principal wall or ‘spiral lamina,’ but are rather offshoots 
from it” *. As seen in a transverse section of the test, these septa 
are not perpendicular to the spiral lamina, but very oblique to it ; and 
on further examination they are found to le nearly parallel to the 
surfaces of a supposed second scroll, concentric with the first, but 
not, like it, constricted at the ends. The lines of intersection of the 
*“‘ secondary ” septa and ‘“‘ primary ” lamina make, therefore, curved 
or oblique outlines on the surfaces of the latter. The septa show, 
however, as straight or nearly straight lines in longitudinal and tan- 
gential sections. 
A series of ‘‘ tertiary ” ingrowths further pass between the opposed 
surfaces of the “primary ” lamina and these and the “secondary ” 
septa. These processes are in the form of pillars, and are arranged 
in rows, longitudinally and transversely, appearing most regular 
in a longitudinal section. They are at right angles, or nearly so, 
to the “primary” lamina. The structure is further complicated by 
the fact that the “ tertiary ” columns, where they attach themselves 
to the spiral lamine at their distal extremities, expand into a more 
or less regular cross-shaped form, the arms of which, uniting with 
those from the neighbouring pillars, form a reticulated framework. 
This, owing to the regularity of position of the columns, may almost 
be considered as forming a system of crossed rafters supporting the 
“roof” of the space contained between each two consecutive folds of 
the “* primary ” lamina, while the columns do not show any such ex- 
pansion on the “floor.” The spaces between the expansions or 
rafters, constituting a series of imperfect chambers, are further filled 
with a loose cancellated growth, which sometimes depends more than 
halfway to the “ floor.” This represents the system of “irregular 
anastomosing tubes” and “parallel columnar or tubular processes ” 
occupying a like position in LZ. persica; but in the form now under 
consideration, probably owing to the greater size of the calcareous 
particles in proportion to that of the test, and its consequent rougher 
construction, no distinct tubulation is recognizable. 
The greatest number of convolutions of the “ primary” lamina 
actually observed is seventeen. Ten is a very common number in 
average-sized specimens. ‘The average breadth of the space enclosed 
between two successive conyolutions of the lamina is one hundredth 
of an inch; and this is maintained with considerable regularity, 
though in young specimens the first two or three whorls are much 
less. The “tertiary” processes or pillars, and the bars of the reti- 
culated framework connected with them, are generally in diameter 
from one four-hundredth to one three-hundredth of an inch, very 
rarely as much as one hundredth. 
The ‘“‘ primary” lamina, as in LZ. persica, is a thin and definite 
wall, generally appearing in microscopic sections as a well-defined, 
* Op. cit. p. 743. 
