NOTES ON RETICULARIAN RHIXOPODA. 53 



Foratninifera of a great variety of size and contour are 

 embraced under this one specific name. Between straight 

 and arcuate specimens no line can be drawn ; again, some 

 individuals are stout and few-chambered, each fresh segment 

 being considerabl.y larger than the previous one, whilst 

 others have many chambers, are thin, and taper very gra- 

 dually; some specimens are rough and sandy externally, 

 whilst others are nearly smooth, the sand-grains being 

 almost completely incorporated by the cement. In size the 

 variation is correspondingly wide ; minute specimens measure 

 but half a millimetre, Avhilst large ones sometimes attain fifty 

 times that length. The area of distribution is very wide; 

 the finest specimens have been found at stations in the South 

 Atlantic and in the North and South Pacific Oceans, at 

 depths of from 1400 to 2000 fathoms. 



Reophax membranacea, n. sp. PI. IV, fig. 9. 



Characters. — Test long, slender, tapering, arcuate, or 

 nearly straight ; consisting of several (five to ten) subcylin- 

 drical or elliptical segments joined end to end. Walls thin, 

 chitinous, beset with minute, adherent sand-grains ; often 

 transversely wrinkled. Length -L \\\ inch (1'4 millim.). 



It has long been known that, within certain limits, the 

 composition of the investment of the testaceous Rhizopoda 

 depends upon what may be termed accidental circumstances — 

 conditions, namely, such as the degree of salinity of the 

 w;iter, its depth, the nature of the bottom, and similar ex- 

 traneous influences. Illustrations of this fact have already 

 V)een adduced from the genera Miliola and Trochammina. 

 The former of these has normally a compact calcareous shell of 

 purcellanous texture, the latter a smooth calcareo-arenaceous 

 test ; but both of them by degrees lose their calcareous 

 nature in water holding a deficiency of inorganic salts in 

 solution, as in brackish pools and river estuaries, and become 

 chitinous or chitino-arenaceous. 



In one or two deep soundings from a very muddy bottom 

 minute moniliform Lituolce have been found with a delicate 

 investment of light brown tint and nearly transparent. The 

 test is very thin, and is only partially soluble in v/eak acids ; 

 it appears to consist of calcareous and chitinous matter, with 

 sometimes a few very minute adherent or embedded siliceous 

 sand-grains. The mineral constituents exist in sufficient 

 quantitv to eiFtrvesce slightly with an acid, and to render 

 the test brittle rather than flexible after it is dried; but the 

 surface is wrinkled transversely, in a manner strongly sug- 



