38 



THE FOEAMINIFEEA 



processes, as in Calcariua and Tinoporus. This 

 exogenous shell layer, which was termed the in- 

 termediate or supplemental skeleton hy Carpenter, 

 is usually accompanied by a secondary stoloniferous 

 system, called interseptal canals. Carpenter regarded 

 this structure as a residual one, resulting from the 

 imperfect junction of the septa and the supple- 

 mentary skeleton, thereby causing certain portions 

 of sarcode to be surrounded or partially cut off, 

 although, in many cases, communication is probably 



Fig. 24. — External Layer in Cycloclypeus Carpenteri, showing 

 Cones of Kon-tubular Substance in the Tubulated 

 Shell-wall. Magnified. After Carpenter. 



kept up for nutritive purposes between them and the 

 sarcode in the chambers of the shell. 



The Shell Texture, 



There are two principal types of shell texture in 

 the Foraminifera, known as the porceUaiioni^ and 

 the 111] aline, which are usually taken as fundamental 

 in classifying this order of animals. Two other 

 prominent t3^pes of shell texture are also met with, 



