10 FORAMINIFERA 



In a few groups such as illustrated in the genus Psammo- 

 sphaera, there is a high degree of selectivity. The North At- 

 lantic species although they build a simple, more or less globu- 

 lar, single chambered test show the following selective char- 

 acters: Psarymwsphaera fusca (PI. 3, fig. 13) uses only sand 

 grains of various sizes, those of one color sometimes being used 

 to the exclusion of others; P. parva (PI. 3, fig. 15) uses sand 

 grains of more or less uniform size and usually adds a single 

 large acerose sponge spicule which is built into the wall and pro- 

 jects on either side often to a distance greater than the diameter 

 of the test itself. That this is accidental can not be held, for the 

 specimens without the spicules are few and I have never seen 

 one with a short or broken spicule, but always with a very long 

 uninjured one; Proteonina testacea (PI. 4, fig. 8) builds its test 

 of other foraminiferal tests and lives as would be expected in 

 Globigerina-ooze; the tests vary in size and shape but sand 

 grains or spicules are not used even though in the same bottom 

 sample may be other genera and species largely made up of 

 spicules or sand grains; Psammosphaera howmanni (PI. 5, fig. 

 16) uses only mica flakes which cemented together by their edges 

 make a weak and irregular test, and the selective power must be 

 great for in most bottom samples the amount of mica flakes is 

 not great; P. riistica (PI. 5, fig. 15) uses acerose sponge spicules 

 for the framework of the test, fitting smaller pieces of broken 

 spicules into the polygonal areas in such a manner that they 

 completely fill the openings. If the material is ingested in the 

 protoplasmic body and then carried to the surface and cemented, 

 it is not difficult to account for the apparent mechanical ability 

 of the organism. That this selection occurs in single celled 

 forms which are but a speck of protoplasmic material is the 

 great wonder. 



The cement of the test may be apparently chitinous in the 

 most primitive forms and there is merely an agglutinating of 

 the materials to the outside of the primitive chitinous test. In 

 the majority of arenaceous forms from the Palaeozoic to the 

 present oceans, the cement is ferruginous and has a yellowish- or 

 reddish-brown color. This may be in a small amount as in 

 Rhabdammina (PI. 2, fig. 9) or in very large proportion as in 

 such genera as Ammolagena (PI. 9, fig. 17) where the arenace- 

 ous particles are very inconspicuous. Siliceous cement is used 



