NOTES ON RETICULARIAN RHIZOPODA. 263 



One of the most important modifications of the normal por- 

 cellanous condition of the tests of the Miliol(E is exemplified 

 in the forms with rough, arenaceous exterior. There are 

 amongst the "Challenger" dredgings at least six tolerably dis- 

 tinct species possessing this character^ and probahlj' not more 

 than two of them have been previously described. One of the 

 two is the well-known Quinqueloculine form, Q.agglutinans, 

 d'Orb. ; the other an elongate, compressed, biconvex species, 

 of somewhat obscure structure {Spiroloculina celata, Costa), 

 the test of which is composed of uniform fine sand-grains, 

 the course of the chambers scarcely traceable on the exterior, 

 and the aperture minute and round. 



Descriptions of two of the new species are given on a later 

 page; the others, which it would be difiicult to render in- 

 telligible without the aid of figures, must be left for the present. 



Allusion has been made in my previous paper to the 

 changes that take place in the composition of the tests of 

 some of the 'Arenaceous Foraminifera which live in water 

 containing less inorganic matter in solution than that of the 

 open sea, and a like alteration is to be observed in the shells 

 of certain 3Iiliola under similar local conditions. The 

 brackish-water representative of this group, Quinqueloculina 

 fusca, has a chitinous or chitino-arenaceous test in place of 

 the normal calcareous shell, precisely resembling in its 

 chemical and physical characters that of the arenaceous 

 Tfoc/mwi?n?V?«,living under analogous deteriorating influences. 



But there is another modification of the chemical compo- 

 sition of the Milioline shell which has not before been observed, 

 which possesses even deeper significance, namely the substitu- 

 tion of clear, homogeneous silica for carbonate of lime. This 

 occurs in very few localities, at stations where the depth 

 registered isgreat (from 2500 to 4000 fathoms), and the bottom 

 consists of Radiolaria-ooze. The specimens are never abun- 

 dant, they are of small size, and consist of a very few inflated 

 segments somewhat irregularly arranged, so as to form 

 gibbous or subglobose shells. The walls are delicately thin, 

 so thin that the organism sometimes collapses on being taken 

 out of fluid and allowed to dry, opalescent or nearly trans- 

 parent, and when quite fresh iridescent. Placed in nitric 

 acid under the microscope there is not a trace of eflfervescence, 

 and no change in appearance is to be detected. It should 

 be remarked that the arenaceous Foraminifera from the 

 same bottoms, such as Trochammina (^Ammodiscus) incerta, 

 are, in like manner, unaffected by treatment with acids. 



The very close connection existing between the various 

 reputed Miliolinegenera,or rather, one might say, the absolute 



