REPORT ON THE FOR AMEN1FERA 
XIX 
as in all the Lituolida:, the walls are built up of foreign particles, siliceous or other, 
combined by means of an inorganic cement so as to produce a strong and often 
highly finished test. Although a considerable amount of selective power is frequently 
manifested, the nature of the extraneous materials is necessarily more or less determined 
by the character of the sea-bottom. Siliceous sand forms by far the most commonly 
employed building material, and sponge-spicules, either entire or in fragments, are also 
frequently used ; but whilst a general preference is shown for siliceous particles, no uniform 
rule prevails, and the same species may be found in one locality building its test, of siliceous 
sand, in a second of coral fragments, and in a third of dead Globigerina- shells. 
From a chemical point of view, the chief questions of interest attaching to these 
arenaceous forms are those referring to the secreted inorganic matter or shell-substance, 
which serves to incorporate the extraneous particles of which the test is mainly constructed. 
The amount of inorganic “mortar” or “cement” varies exceedingly, not only in different 
species, but in individuals of the same species from different localities. 
In Rhizammina , which takes the form of long, flexible, branching tubes, the mineral 
particles appear to be attached to the organic envelope without the assistance of any 
secreted inorganic matter. 
Rliabdammina abyssorum, the test of which consists of rigid tubular arms radiating 
from a centre, furnishes an example of variability both as to chemical and physical 
characters. The following analyses are from examples obtained from different and 
widely separated localities. No. I. refers to specimens of light reddish-brown hue and 
rough exterior, dredged in the North Atlantic; No. II. to specimens of very dark colour, 
and comparatively smooth exterior (owing to the presence of a much larger proportion 
of cementing material) dredged in the Pacific, just south of the equator, between Papua 
and the Admiralty Islands. 
Rhabd ammina ab yssorum. 
i. 
n. 
Silica, . . . . 
94-7 
88-26 
Ferric oxide, . . . . 
2-4 
7-41* 
Carbonate of lime, 
2-9 
4-01 
100-0 
99-68 
* Including a small quantity of alumina not separately estimated. 
The closely related genus Hyperammina displays as great or perhaps even greater 
diversity in the texture and superficial characters of the test, and a corresponding 
variability as to the relative proportions of extraneous and secreted constituents. The 
chemical examination of Hyperammina friabilis, a large species with thick walls composed 
of loosely aggregated sand, gave results differing but little from those yielded by the 
rougher specimens of Rliabdammina , above quoted. 
