120 PROTOZOA. 



Eocene). At this period in the earth's history we find the 

 ISTummulites existing in extraordinary profusion, and building 

 up the wide-spread and massive series of calcareous deposits 

 which are known as the " Nummulitic Limestone." Accord- 

 ing to Sir Charles Lyell, " the Nummulitic Limestone, with 

 its characteristic fossils, plays a far more conspicuous part 

 than any other Tertiary group in the solid framework of the 

 earth's crust, whether in Europe, Asia, or Africa. It often 

 attains a thickness of many thousand feet, and extends from 

 the Alps to the Carpathians, and is in full force in the north 

 of Africa, as in Algeria or Morocco. It has also been traced 

 from Egypt, where it was largely quarried of old for the 

 building of the Pyramids, into Asia Minor, and across Persia, 

 by Bagdad, to the mouths of the Indus. It occurs not only 

 in Cutch, but in the mountain-ranges which separate Scinde 

 from Persia, and which form the passes leading to Cabul ; 

 and it has been followed still further eastwards into India, 

 as far as Eastern Bengal and the frontiers of China." In. the 

 later Tertiary period, the genus underwent a striking de- 

 generation ; and it is represented at the present day by only 

 a few small forms, which are found in arctic, temperate, and 

 tropical seas. 



Very closely allied to Nummulina, and of equal or even 

 greater geological importance, is the genus Fusulina, the 



typical forms of which (fig. 

 24) are spindle-shaped in 

 figure, and may be compared 

 to a Nummulite drawn out 

 at its umbilici. According to 

 Brady, however, some spe- 

 cies of Fusulina are discoidal and symmetrical, and thus not 

 distinguisTiable in form from Nummulina ; while in other 

 species the test is spherical. In internal structure, and es- 

 pecially in the minute tubulation of the shell-substance, the 

 genus approaches Nummulina, but a regular interseptal 

 " canal-system " appears to be wanting, and the chambers 

 are broken up into chamberlets. Most of the Fiisulince are 

 of considerable size, often from a third to a half of an inch in 

 length, and they often constitute massive beds of limestone, 



