190 



Marine Investigations iu South Africa. Vol. V. 



siliceous grains are so arranged in building up the wall that they 

 form a network of minute chambers communicating freely with each 

 other, and perforated with tubular-like passages opening out freely 

 into a main central chamber, supplemented and strengthened at 

 intervals by the extension of a portion of the walls into the interior ; 

 in the form of septa, constructed, like the remainder of the test, of 

 cemented sand-grains (PL XX., figs. 8, 9). 



These chambers, having free communication with each other, are 

 generally quite filled with green sarcode, containing nuclear (?) 

 corpuscles. Diameter of the central chamber variable (m. di. J„ inch 

 = 1-26 mm.), internal chitinous lining absent. The pseudopodial 

 apertures are situated at the extreme or peripheral ends of the 

 pinnate outgrowths (see woodcut), formed sometimes of three or 



a^ 



~ A. 



... .,??#' 



Front view of a peripheral end of one of the pinnate outgrowths of Botcllma 

 pinnata, sp. nov., after it has been treated with dilute hydrochloric acid. 

 Magnified 12 diameters; a, a, pseudopodial apertures. 



fouj- transverse slits, or more generally of irregular spaces between 

 the agglutinated sand-grains. These apertures are almost closed in 

 with a light brown cement made up of carbonate of lime and ferru- 

 ginous material, from which extend minute transparent spicules also 

 formed of carbonate of lime, produced to all appearance by the 

 organism itself as a protective agent. These portions are of a 

 much paler colour than any other part of the test, due to a higher 

 percentage of lime at these points than elsewhere, giving a bright 

 and life-like effect to the whole structure. 



On the test being laid open longitudinally, the main central 

 chamber is seen to start from a large primordial cell, from whence a 

 main passage runs through the whole structure, branching off into 



