110 THE FOEAMINIFEEA 



without any definite aperture, for the sarcode Hows 

 out between the interstices of the coarse sand- 

 grains which form the investment. 



An agglomerated series of spherical or sub- 

 spherical chambers results in a form like the genus 

 Horosplicvra. In Saccainmiiia the walls of the test 

 are more firmly cemented, and a distinct orifice is 

 present. In the fossil species, found in the Carboni- 

 ferous limestone {8. fusiiliniformis), the shell-wall 

 is partly arenaceous and partly calcareous ; or, 

 perhaps more correctly, consists of calcareous grains 

 with a partially calcareous cement (subarenaceous) ; 

 and there is a tendency for the subglobular or 

 fusiform segments to form a connected series of 

 chambers united by a short stolon or necklike 

 prolongation, instead of breaking off as a separate 

 individual after reproduction, as in the recent 

 >S'. sphcEvica. On the other hand the recent 

 /S. socialis shows some affinity towards the fossil 

 form in its tendency to assume a lateral plan of 

 serial budding, the segments being formed side by 

 side, with their apertures directed outwards. 



Other similarly rudimentary types have their 

 tests composed of sponge spicules selected by the 

 organism from the surrounding mud ; these may be 

 more or less closely felted together, and mingled in 

 some cases with a small proportion of the mud. 

 These spicular forms are chiefly found in the sub- 

 family P1LITLININ.E. 



The tubular modifications of the Astrokhizid.e 

 frequently consist of a simple tube with constric- 



