54 HENRY B. BRADY. 



gestive of a membrane covering a soft or plastic mass. Unfor- 

 tunately the species is very rare, and the specimens exceed- 

 ingly small, so that material does not exist for any close 

 investigation as to the chemical nature of the test, nor is 

 sufficient known of the condition of the -sea bottom, in these 

 cases, to account for the deviations from the normal type of 

 structure. 



The best examples hitherto procured of R. memhranacea 

 are from 1900 fathoms, off the coast of South America, in 

 about the same latitude as Buenos Ayres. 



Reophax spiculifera, n. sp. PI. IV, figs. 10, 11. 



Characters. — Test elongate, straight or arcuate ; consisting 

 of a few (three to six) cylindrical segments. Shell-wall 

 composed of siliceous spicula arranged side by side, and 

 firmly cemented together. Spicula often protruding more 

 or less from the base of the segments. Length -^^ inch 

 (I'O millim.). 



This is one of the many species of Foraminifera that give 

 evidence of considerable selective power in respect to the 

 material employed for the construction of their tests. That 

 it is selective power, and does not depend upon the absence 

 of the angular sand-grains, which are the ordinary con- 

 stituent of the composite shells of the Lituol<s, is rendered 

 pretty certain by the fact that other species occur in the 

 same soundings in their normal sandy condition. Again, 

 the orderly arrangement of the spicula side by side and 

 the neat and compact masonry of the walls cannot be acci- 

 dental, contrasting strongly as it does with the indiscrimi- 

 nate use of sponge-spicula amongst sand-grains and various 

 other extraneous bodies, seen in the tests of the rough 

 Lituoline forms. 



Reophax spiculifera is, comparatively speaking, a minute 

 species, being seldom more than -^l inch (1 millim.) in 

 length. It occurs at several of the " Challenger" stations 

 in the South Pacific, at depths varying from 250 to 2300 

 fathoms, generally on muddy bottoms. 



Ge?m5— TROCHAMMINA, Parker and Jones. 



The genus Trochammina was established by Messrs. 



Parker and Jones,' for a group of arenaceous Foraminifera 



characterised primarily by their thin, smooth, finely-cemented 



tests. Although the name was originally applied to a Rotali- 



» ' Annals and Mag. Nat. Hist.,' 1859, ser. 3, vol. iv, p. 347. 



