NOTES ON RETICULARIAN UUIZOPODA. 27 



and lastly, as it can be shown that Foraminifera have the 

 power of secreting silica even to the extent of forming a 

 continuous shelly investment, the easiest explanation of the 

 fact that so many composite tests are not disintegrated by 

 the action of acids, lies in the supposition that secreted silica 

 enters more or less into their composition. At the same time 

 it is quite clear that the precise nature of the investment 

 of many normally arenaceous types is a matter depending 

 largely on external or accidental circumstances. 



The fuller consideration of these and kindred matters will 

 arise naturally in the description of the organisms in which 

 they form characteristic features, so that without further 

 preface we may proceed to a review of the more interesting 

 forms belonging to this particular group of Khizopods. 



PsAMMosPH^RA FUSCA, F. E. Schulze. PI. IV, figs. 1, 2. 



Psammosphcera fusca, F. E. Schulze, l^l'^i. II. Jahresberichte d. Komm. 

 Untersuch. d. deutsch. Meere iu Kiel, p. 113, pi. 

 ii, fig. 8, a—f. 



This is one of the simplest of the arenaceous Foraminifera, 

 and although small specimens are not uncommon in deep water, 

 it remained undescribed until the publication of Professor 

 Schulze's memoir in the North Sea researches above quoted. 

 Tenor twelve years ago I found it in considerable abundance 

 in one of the " Bulldog" soundings obtained by Dr. Wallich, 

 but the specimens were all very small, and it was then difficult 

 to decide whether they were Foraminifera or not. It has been 

 the custom to consider that the tests of the arenaceous Rhizo- 

 poda are of necessity imperforate ; in other words, that except 

 the single conspicuous pseudopodial orifice the investment is 

 non-porous, and the fact of these specimens having no general 

 aperture seemed to throw doubt upon their nature. But it 

 is now evident that the term " imperforate " is only applica- 

 ble to a limited number of genera, and that some at least of 

 the sandy forms have more or less porous tests, though, 

 owing to the irregularities of the surface and their rough 

 texture, thfi orifices are traced with difficulty. 



Schulze's description of the species is quite accurate as 

 applied to large specimens. They are spheroidal bodies, from 

 two to four millim. {-^ to ^ inch) in diameter, without any 

 perforations visible to the naked eye, commonly free, but occa- 

 sionally adherent to small stones. The test itself is from '25 to 

 •5 millim. thick, and is composed of coarse sand-grains, united 

 by a cement of fine texture and of characteristic grey-brown 

 colour. Whilst the exterior is more or less rough, owing to 



