226 THE FOEAMINIFEEA 



tropical areas in its best developed condition, al- 

 though small forms are occasionally met with even 

 on the shores of the British Islands. It is commonest 

 in shallow-water sands. As a fossil this species dates 

 from the Miocene. (Plate 12, fig. P.) 



Genus Miogypsiua., Sacco. 



Test consisting of a median spiral series of 

 chamberlets, with superimposed lateral layers of 

 acervuline segments. Oligocene, Miocene, mid (?) 

 Mecent. 



Example. — M. convplctnata., Schlumberger, ' Bull. 

 Soc. Geol. France,' ser. 3, vol. xxviii., 1900, p. 300, 

 pi. ii. figs. 13-16 ; pi. iii. figs. 18-21. 



Shell discoidal, undulate, with the contour very 

 irregular. The surfaces studded with protuberances, 

 the ends of pillars inserted between the chamberlets. 

 Test perforate. In the young individuals the central 

 protuberance indicates the position of the internal 

 spire. OUgocene {Aquitanian) of St. Etienne d'Orthes 

 (liandes). 



It is probable that the so-called Gijpsina vesicn- 

 laris, var. discus of Goes, occurring in coral areas of 

 the present day, is a degenerate form of Miogi/psina. 



Genus Polytrema, Eisso. 



Test parasitic ; encrusting or arborescent ; surface 

 areolated, colour usually orange, scarlet, or pink, 

 sometimes white. Interior partly occupied by small 

 chambers arranged in more or less regular layers, and 

 partly by non-segmented canal-like spaces, often 



