185 



CHAPTER XIII 



THE FAMILY LAGENID^E 



The simplest type of shell in this family is the mono- 

 thalamous Lagena, which is a flask-shaped, sub- 

 spherical, or flattened chamber with a single orifice. 

 The various generic types comprised wdthin this 

 family are the result of a successional growth or bud- 

 ding of a series of lageniform chambers joined 

 together in various ways and on certain definite plans. 

 When, for instance, the chambers are attached in a 

 moniliform series by their ends, we have a form like 

 Nodosaria ; in a curved series, MarginuUiui ; in a 

 spiral series, CristeUaria ; in alternating double or 

 triple series, PohjnwrjjJiuta, and so on. 



The type of shell-structure is the hyaline or vitre- 

 ous ; the shell-wall is finely perforated and usually 

 thin. There is no trace of a double shell-w^all or double 

 septum, as in the Rotaline and Nummuline types 

 of shell-structure. But although the shell-wall is 

 simple in its construction, it is often variously orna- 

 mented on the surface with hexagonal meshwork, 

 strong riblets, fine stride, or series of punctations, 

 which, however, do not show the laminar structure 

 seen in the exogenous shell-growth of the Eotalines 

 and other forms of an advanced type. 



