108 THE FOEAMINIFERA 



CHAPTEK IX 

 THE FAMILY ASTEOEHIZID.E 



General Characters and Affinities. — Test invari- 

 ably composite, usually of large size and monothala- 

 mous ; often branched or radiate, sometimes seg- 

 mented by constriction of the ^Yalls, but seldom or 

 never truly septate ; polythalamous forms rarely 

 symmetrical. 



The various genera of this group are all arenace- 

 ous in their shell structure ; and this series, together 

 with the succeeding family of the Lituolid^ and 

 the portion of the family Textulariid^ consisting 

 of the arenaceous types, form the comprehensive 

 group of the Arenacea of Eupert Jones and the ' kiesel- 

 schalige Foraminiferen ' of Von Eeuss. The material 

 of which the test is composed comprises coarse or 

 fine sand-grains (quartzose), line arenaceous mud, 

 admixtures of calcareous mud and sand, sponge 

 spicules felted together or made coherent by sarcodic 

 cement, the agglomerated tests of other Foramini- 

 fera, or, in rare cases, merely of an investment of 

 chitinous substance with or without a meagre stiffen- 

 ing of line sand. 



The majority of the forms wdiich are comprised 

 in the Family AsTRORmziD.E, owing to their generally 



