Brackish-water Fi oraminifera. 277 
The latter species has, in place of the normal porcellaneous 
shell, an investment consisting of a horny membranous basis 
solidity of the test, that prolonged treatment with an acid does 
not materially change its form or appearance; nor, beyond 
slightly increasing its transparency, does it appear to produce 
any alteration in its minute structure. A portion of the cara- 
pace of a specimen in its natural state is represented, highly 
magnified, at Pl. XI. fig. 3a, and a similar piece, decalcified 
by strong acid, is shown in fig. 3b; both are from prepara- 
cm mounted in Canada balsam, and viewed by transmitted 
ight. 
The Lituolida with variable but essentially composite tests 
have their best brackish representative in Trochammina in- 
lata. Under similar enfeebling conditions, they show a ten- 
dency to change in the same direction. e deposit of calca- 
in size; on the contrary, the finest specimens of 7r. inflata we 
have seen were of this membranous sort. 
The chemical nature of the investment is similar to that of 
Quinqueloculina fusca. Large specimens have been treated 
With nitrie and hydrochlorie acids, and strong solution of 
caustie potash, without sensible change, preserving sufficient 
solidity and firmness to permit of being mounted in Canada 
balsam, at the end of the process, without fracture. 
The Lagenida do not appear to subsist where they are un- 
able to produce their normal hyaline shell: no examples have 
been met with in the gatherings furthest removed from the 
sea; and in the other localities they do not differ from marine 
Specimens. 
monly thin-shelled and dark-coloured ; and it has more than 
Once occurred to us whether these brackish organisms, which 
