14 SlDEBOTTOM, Foraminifera from tJie Island of Delos. 



Polymorphina lactea, var. concava, Williamson. (PI. 3, 

 figs. 8, 9,) 



Polymorphina lactea, var. concava, Williamson ('58), 

 p. 72, pi. 6, figs. 151, 152. 



P. concava (Williamson), Brady, Parker and Jones 

 ('70), p. 236, pi. 40, fig. 32. 



This curious little foraminifer seems to have a place 

 of its own among the Polymorphinae. Williamson's 

 description of this species runs as follows : — " Its centre 

 consists of a small hyaline shell of the ordinary type, but 

 the last segment is spread out into a thin marginal 

 expansion ; highly concave on one surface, where the 

 previous segments are but faintly visible (fig. 152) and 

 equally convex on the other, where the earlier segments 

 of the shell are more conspicuous. The periphery is 

 always sinuous, and though very thin, is rounded and 

 obtuse. The last segment presents no visible septal 

 orifice. I am disposed to believe that during the forma- 

 tion of the ultimate segment, the individuals belonging to 

 this variety may have become parasitic upon some other 

 rounded bodies ; an opinion to which the variable contour 

 of the peripheral segment, contrasted with the uniform 

 appearance of the central ones affords some countenance." 

 Now, the last segment referred to in the above quotation 

 I think may be understood to have a floor which attaches 

 itself to the lower surface of the shell, and is shaped 

 according to the object to which it is adherent. This 

 forms a chamber, the sides of which spring like an 

 arched ceiling, until they reach the upper surface of the 

 shell, thus completing a chamber round the central test. 

 About twenty specimens were found, of which fifteen are 

 attached to various objects, generally on their more or 

 less flat surface, but in one case the test is attached in the 



