FORAMIXIFERA OF TASMANIA. 345 



stone is broken, and are therefore chiefly seen in section, the white 

 lines of the chambers showing up very distinctly on the dark 

 ground of the stone in which they are set. 



The prevailing foraminifer (which occurs in this bed in astonish- 

 ing numbers) undoubtedly belongs to the genus Nubecularin. 

 This is evident, not only from its exhibiting the mode of growth 

 characteristic of the genus, but is confirmed by the transparent 

 sections, which show the test to be imperforate, whilst the objects 

 give by transmitted light the dark-brown color that is eminently 

 characteristic of the porcellaneous group to which Nubecularia 

 belongs. The minuteness of the objects, coupled with the hard- 

 ness of the matrix, renders it almost impossible to obtain examples 

 of this form in a free condition, and it is not easy to mark off with 

 clearness specific distinctions where the data are limited almost 

 entirely to transparent sections. This is especially the case when 

 dealing with a genus of so protean a habit of growth as the one 

 imder discussion ; j'et for reasons assigned below we have thought 

 it advi.=able to give a varietal value to the features which distinguish 

 these remote geological representatiA'es of the genus from the 

 closely-related modern Nubecularia lucifuga. It is with pleasure . 

 that I associate the name of Mr. Thomas Stephens, M.A., F.G.S., 

 with this interesting foraminifer, for reasons that will be apparent. 



NUBECULARIA LUCIFUGA, Var. STEPEEXSI, Var. Nov. 



Habit of growth closely resembling the type. Initial chamber,, 

 globular. Subsequent chambers, elongated and slightly inflated. 

 Chambers arranged, either on a spiralline plan, in rectilinear order,, 

 or in irregular acervaline masses. Walls of the test, thin, uniform 

 in thickness, and sharply defined in outline. Septal divisions 

 marked on exterior surface by sunken lines. 



A comparison of transparent sections of recent examples of 

 N. lucifuga, and the form now under description, reveals a striking 

 difference in the partitional walls. In the recent examples the 

 walls are thick, irregular, and sometimes membranous, Avhilst the 

 fossil form jjreserves a remarkably uniform thickness in its septal 

 partitions. In existing examples the sutural lines are generally 

 more or less obscured by an excessive deposit of shell substance on 

 the exterior surface. The Tasmanian specimens, on the other 

 hand, do not thicken the periphery by secondary deposits of shell 

 substance, as is frequently the case with living forms. The present 

 descriptions can only be taken as provisional. Should a portion of 

 the rock in which they are contained be discovered sufficiently 

 fi-iable to yield the Nubeculariw in a free condition, it may be 

 found that they are practically identical with the recent species, 

 or the differentiation may receive a higher value, reqiiiring a 

 specific rather than a varietal distinction fi-om the existing species. 



The geological range of the genus is extensive, although it has 

 apparently found its maximum development in existing seas, and 



