REPORT ON THE FORAMINIFERA. 
XVII 
area of the North Atlantic , 1 the subject was mentioned and the supposed source of error 
pointed out ; and since then Mr. Schmelck has been good enough to forward me a 
memorandum of an independent analysis of Biloculina, made by himself, which is as 
follows : — 
Carbonate of lime, . . . . . . . 92 , 05 
Insoluble in hydrochloric acid, . . . . . . 7 '61 
99-66 
The difference between the various genera of Miliolinince is purely morphological, 
and, chemically speaking, whatever is true of one is pretty sure to apply in a greater or 
less degree to all. It is therefore interesting to remember in connection with the presence 
of silica in Biloculina , that at certain Stations in the abyssal area of the North Pacific 
and elsewhere, manifestly unfavourable to the existence of calcareous organisms, 
Miliolinince are occasionally found, the tests of which are scarcely affected by acids, the 
normal calcareous shell being partially or sometimes wholly replaced by a thin, 
translucent, siliceous investment. 
It is well known of course that some few species of Miliolina are normally encrusted 
with siliceous sand ; but the porcellanous forms to which reference has been made are 
such as have white calcareous shells with polished exterior, and thin sections of the 
test exhibit a perfectly homogeneous texture. 
Orbitolites complanata, var. laciniata. 
i. 
n. 
hi. 
IV. 
Silica, ...... 
0-58 
0-3 
0-14 
0T1 
Carbonate of lime, ..... 
86-46 
88-2 
88-74 
87-91 
Carbonate of magnesia, .... 
12-52 
8-8 
9-55 
10-50 
Alumina, with phosphates of lime and magnesia, 
2-7 
Alumina and ferric oxide, .... 
0-68 
... 
100-24 
100-0 
98-43 
98-52 
Of the more complex Porcellcmea the genus Orbitolites has naturally been selected 
for chemical examination, not only on account of the size of the specimens, but because 
of the abundance and importance of the type as a constituent of the coral-reef fauna. 
The separate analyses of two specimens of Orbitolites complanata, var. laciniata, gave the 
somewhat different results recorded in Columns I. and II. of the preceding table. A number 
1 Norwegian North Atlantic Expedition, 1876-1878. Chemistry. — II. On Oceanic Deposits, by l^udwig Schmelck. 
Christiania, 1882. 
(ZOOL. CHALL. EXP. PART XXII. 1884.) Y C 
