FROM THE FUNAFUTI ATOLL. 19 
H. simplex, VOrbigny, 1846, Foram. foss. Vienne, p. 211, pl. xii. 
figs. 12-14. 
H. helvetica, Kaufmann, 1867, Geol. Beschreib. des Pilatus, p. 153, 
pl. ix. figs. 6-10. 
_ HI. depressa, var. simplex, VOrbigny, Goés, 1882, Retic. Rhizop. 
Caribb. Sea, K. Svenska Vet.-Akad. Handl. vol. xix. no. 4, p. 117, pl. viii. | 
fig. 303. 
H. depressa, VOrbigny ; Brady, 1884, Rep. ‘Chall.’ vol. ix. p. 746, 
pl. exii. figs. 14-20; Egger, 1893, Abhandl. bayer. Akad. Wiss., math.- 
phys. Cl. ii. Bd. xviii. Abth. ii. p. 241, pl. xx. figs. 34, 35; Goés, 1896, 
Bull. Mus. Comp. Zool. Harvard, vol. xxix. no. 2, Memoir xx. p. 79. 
As Dr. H. B. Brady has already pointed out in his monograph 
on the ‘ Challenger’ Foraminifera *, H. depressa can be arranged 
in two series according to their form and external characters. 
After a careful study of the Funafuti specimens, I have been 
able to identify these two series with the dimorphic forms A and 
B respectively. The megalospheric form (A) embraces the 
involute, bi-convex type, with the asymmetric (spiral) flange ; 
whilst the microspheric form (B) is represented by the com- 
pressed and explanate specimens. The difference between the 
primordial spheres of the two forms is not very great, but it is 
constant, their diameters being in the ratio of 3: 2. 
The megalospheric form is far more common than the micro- 
spheric, for in most samples it is in the proportion of about 500 
to 1, or even greater. 
The megalospheric form in H. depressa attains a larger diameter 
in full-grown specimens than the microspheric, which is unusual 
amongst the Foraminifera yet examined with regard to dimorphism, 
but nevertheless instances are known: for example, in Adelosina 
polygonia, Schlumberger, the megalospheric shell is slightly larger 
than the microspheric (1°5 to 1-4 mm.). 
From so large a collection of specimens as we are now dealing 
with, possibly one of the most extensive from any particular 
locality, one may obtain a very complete idea of the extent of 
variation in a species from a given area. H. depressa im its 
megalospheric furm varies greatly as to size and thickness, ai.d 
the microspheric form varies curiously in its internal septal 
arrangement, to be noticed below. The two forms, however, 
are in themselves so distinct as to present little difficulty in 
relegating them to either series. 
Form B has a thin and transparent, or translucent, shell-wall, 
and thus the septation can be clearly seen. The earlier portion 
shows no secondary septation dividing the chambers into chamber- 
* Rep. Chall, vol. ix. p. 746, pl. cxii. figs 17, 18 19, 20. 
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