AEENACEOUS FORAMINIFERA 



8l 5 



Thurammina papillata (fig. 614, g) a not less remarkable imitation of 

 the Orbuline. This last is specially noteworthy for the admirable 

 manner in which its component sand-grains are set together, these 

 being small and very uniform in size, and being disposed in. such a 

 manner as to present a smooth surface both inside and out (fig. 614, A), 

 whilst there are at intervals nipple-shaped protuberances, in every one 

 of which there is a rounded orifice. A like perfection of finish is seen 

 in the test of Hormosina glcibulifera (fig. 614, c), which is composed 

 of a succession of globular chambers rapidly increasing in size, each 

 having a narrow tubular neck with a rounded orifice, which is 

 received into the next segment. In other species of the same genus 

 there is a nearer approach to the ordinary Xodosarine type, their 

 tests being sometimes constructed with the regularity characteristic 

 of the shells of the true Nodosaria, Plate XIX. ic,. whilst in other 





FIG. 615. Arenaceous Forarninifera : c<, I/, exterior and sectional views of 

 Slieophax sabulosa ; c,Rhabda mmina abyssm-itm ; d, cross section of one 

 of its arms; e, Rheophax scorpiurus ', /, Hormosina Carpenti ri. 



cases the chambers are less regularly disposed (fig. 615, f). having 

 rather the character of bead-like enlargements of a tube, whilst their 

 walls show a less exact selection of material, sponge-spicules being 

 worked in with the sand-grains, so as to give them a hirsute aspect. 

 A greater rudeness of structure shows itself in the ISTodosarine forms 

 of the genus Rheophax, in which not only are the sand-grains of the 

 test very coarse, but small Foraminifera are often worked up with 

 them (fig. 615, e). A straight, many-chambered form of the same 

 genus (fig. 615, a, b) is remarkable for the peculiar finish of the neck 

 of each segment ; for whilst the test generally is composed of sand- 

 graiiis, as loosely aggregated as those of which the test of Astrorhiza 

 is made up, the grains that form the neck are firmly united by fer- 

 ruginous cement, forming a very smooth wall to the tubular orifice. 

 The highest development of the 'arenaceous' type at the present 

 time is found in the forms that imitate the very regular naxtiloid 



