184 FORAMINIFERA 



municating with the interior of the test which is filled with 

 columnar chambers and vertical pillars; wall calcareous, that 

 of the outer surface thin, imperforate; apertures numerous on 

 the ventral face. 



Eocene. India. 



This family contains species which although very similar in 

 their general characters may not have been derived from the 

 same ancestral source. Most of them evidently arose from a 

 Palaeozoic conical form comparable to the young of Am- 

 modiscoides, and as further developed in HowcMnia. 

 Tetrataxis represents an early stage in the series where 

 the division into chambers has taken place. In 



Valvulinella there is a further division into chamberlets. In 

 the higher forms, the flattened chambers are taken on with the 

 aperture on the broad flattened face consisting of numerous 

 pores. Dictyoconoides is a very peculiar form, and probably has 

 its affinities with the Rotaliidae or related families, but is left 

 here until more is known of its relationships. 



FAMILY 22. LAGENIDAE 



Test vitreous, with a glassy lustre; chambers simple, neither 

 biserial, trochoid, nor irregularly spiral, planispiral when coiled ; 

 wall calcareous with very fine perforations; aperture typically 

 radiate but in a few genera simple, in the radiate apertured 

 forms with a small chamberlet below the radiate aperture open- 

 ing into the main chamber by a simple rounded orifice. 



KEY TO THE GENERA 



I. Test mostly close coiled. 



A. Aperture with a rounded opening at the outer angle of the aper- 



tural face Robulus. 



B. Aperture entirely radiate. 



1. Sides typically convex Lenticulina. 



2. Sides typically flattened or concave Planularm. 



II. Test coiled in the early stages at least in the microspheric form. 

 A. Test much compressed. 



1. Ap6rture entirely radiate. 



a. Later chambers extending obliquely back on one side. 



Vaginulina. 



