1 36 PROTOZOA. 



a supplemental skeleton (forming the so-called " marginal cord "), 

 which, together with the septa, is penetrated by a well-developed 

 and ramified "canal-system" (see fig. 26, d). By the researches 

 of Brady, we know now that the range of the genus Nummulina 

 in time must be carried back to the Carboniferous, one small form 

 (viz., Nummulina pristina, fig. 37) having been detected in the 

 Mountain Limestone of Belgium. A few " Nummulites " have also 

 been detected in strata of Jurassic and Cretaceous age, but the maxi 

 mum development of the genus is recorded in the early Tertiary 

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

 find the Nummulites existing in extraordinary profusion, and build- 

 ing up the widespread and massive series of calcareous deposits 

 which are known as the " Nummulitic Limestone." According 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 under- 

 went a striking degeneration ; 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. 39) are spindle- 

 shaped in figure, and may be 

 "SSSSgSSSr- compared to a Nuramulite drawn 



out at its umbilici. According 

 to Brady, however, some species of Fusulina are discoidal and sym- 

 metrical, and thus not distinguishable in form from Nummulina ; 

 while in other species the test is spherical. In internal structure, 

 and especially 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 Fusulina are of considerable size, 

 often from a third to a half of an inch in length, and they often con- 

 stitute massive beds of limestone, which have been justly paralleled 



