234 THE FOEAMINIFEEA 



genous conelike layers of shell. In the latter genus 

 the central disc, resembling Cycloclijpeus, is enclosed 

 between two layers of acervuline chamberlets, which 

 gives to the shell a lenticular contour. It is further 

 modified very frequently by the more rapid growth of 

 the shell along certain radial lines, which imparts a 

 stellate form to the test. 



Buh-family 1. Fusulinin.e. 



Test bilaterally symmetrical ; chambers extending 

 from pole to pole ; each convolution completely 

 enclosing the previous whorls. Shell-wall finely 

 tubulated. Septa single, or rarely double ; no true 

 interseptal canals. Aperture a single elongated slit, 

 or row of small rounded pores, at the inner edge of 

 the final segment. 



Genus Fusulina, Fischee. 



Test fusiform or subgiobular ; chambers entire, 

 or only subdivided by the infolding of the septal 

 wall ; aperture an elongated central fissure. Car- 

 boniferous and Permian. 



Example. — F. cylindrical Fischer, ' Oryctogr. 

 Gouv. Moscou,' 1830-37, p. 126, pi. xiii. figs. 1-5. 



The test of this important rock-forming species is 

 spindle-shaped and rounded at the ends. The shell 

 is marked wdth longitudinal furrow^s, and the slitlike 

 aperture is situated in the centre of the overlapping 

 angle of the septal plane. Carboniferous and Per- 

 mian. 



