1080 The American Naturalist. [ December, 
(4) CEMENTING MATTER. 
In all testaceous Rhizopods the siliceous elements are cemented 
by or sometimes lie on a substance which may be called chitinoid, 
or rather chitino-siliceous. This matter, often quite transparent 
and colorless, but sometimes colored,—yellow, dark purple in some 
Arcellas, pink in Heleopera rosea, chocolate-brown in Assulina,— 
is more or less abundant according to the species. Nearly absent 
in the Difflugias sensu stricto, and in very small quantity in 
Euglypha, Quadrula, etc., it varies considerably in thickness in 
the series of species, generally making an internal varnish to the 
inner side of the shells, thence penetrating between the plates or 
other siliceous elements, sometimes overlapping them at the out- 
side, and forming as it were relief veins or exudation droplets. 
But it never makes up the entire mass of the shell, and it is only 
very seldom (Hyalosphenia) that it constitutes the principal mass 
of the same. 
` I have called this matter chitino-siliceous, because, in fact, I am 
inclined to consider it as consisting of a mixture of chitinoid mat- 
ter and of an infinity of extremely small siliceous’ particles im- 
bedded in the magma. This is but a supposition, yet it may 
perhaps give an explanation of the following facts: This matter, 
in the pure state and without admixture of foreign elements, as it | 
occurs for instance in the genus Centropyxis, resists the action of 
red heat (blow-pipe) or of cold, concentrated sulphuric acid, but 
disappears completely in boiling sulphuric acid. This I would 
explain by saying that in both cases the chitinoid matter is dis- 
solved, but that whilst by mere heating the siliceous particles 
becomes soldered to each other during the process, the convection 
currents in the boiling sulphuric acid disperse them. The follow- 
ing experiment explaining the relations between the plates of the 
shell on the one hand and the connecting matter on the other, 
may at any rate give some probability to the explanation just 
given concerning the chitinoid matrix: I have found that the 
shells of all the testaceous Rhizopods resist both red heat 
(blow-pipe) and cold, concentrated sulphuric acid, but that this 
acid when boiling, after separating the plates from each other, 




