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CHAPTEK XI 

 THE FAMILY TEXTULAKIID^ 



In this family the usual texture of the test is 

 arenaceous ; hut this is hy no means a rule, for nearly 

 all the smaller species are hyaline, and in some cases 

 this type of shell-structure is typical of an entire 

 genus. 



The relationships of the various types constituting 

 this family are very apparent from the fact that the 

 connecting links are numerous, and the plans of 

 growth, though diverse, are of definite conformation. 

 The general plans on which the shells are constructed 

 are either as a double series of segments placed 

 alternately in relation to each other, and in the same 

 plane of growth, or as a triserial group of segments ; 

 in certain genera the double or triple series is spi- 

 rally tw^isted ; in others the arrangement is confused. 

 There is also a tendency for certain forms to take 

 on, at different stages, diverse lines of growth, 

 usually from the more complex to the simpler ; as, 

 for example, Bifjeiicrii/ci, which begins with a biserial 

 arrangement followed by a uniserial set of segments ; 

 or Clai'JiJii/n, which is at first triserial and afterwards 

 uniserial. 



The sub-family of the Textulaeiin.e consists of 

 those forms which are either biserial or triserial, and 



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