IN THEIR ROLE AS WORLD-BUILDERS. 5> 



simple type Lagena, which are still existing, and of world-wide 

 distribution. These and the Spirillina Groomii of Chapman 

 (= S. vivipara Ehrenberg) are therefore probably the oldest 

 living types now in existence. 



Of greater interest is the recording by Chapman (14) and 

 Vine (15) of two genera of arenaceous Foraminifera, viz. Hyperam- 

 mina and Stacheia from rocks of the Wenlock series. These 

 constitute, so far as we are aware, the earliest evidence of the 

 existence of arenaceous Foraminifera. The geological record 

 does not furnish any evidence in support of the theory, so fre- 

 quently postulated, that the earliest Foraminifera were types 

 Avith adventitiously constructed tests \ nor do we see any reason 

 for accepting this theory. The property of secreting mineral 

 salts from the surrounding medium is common to organisms of 

 all grades, whereas the power of selecting and utilising foreign 

 material seems to indicate a later and higher stage of develop- 

 ment. There appears to be no geological reason why the 

 composite tests of arenaceous Foraminifera should have escaped 

 fossilisation, when the delicate shells of -calcareous genera were 

 preserved, had the two groups been in existence together in pre- 

 Silurian times. 



The Devonian period, according to Chapman (16), presents 

 but a single record of Foraminifera, viz. those discovered by 

 Terquem (13) at Paffrath in the Eiffel. Chapman comments 

 on the singular absence of Foraminifera in the Devonian seas, 

 where the conditions for their existence appear to have been 

 favourable. 



With the next period, however, the Carboniferous, the Fora- 

 minifera first begin to justify the title of our paper as Worldr 

 builders. Various genera make their appearance in such 

 numbers as to form enormous deposits. In the lower Carbonif- 

 erous strata the large arenaceous species known as Saccammina 

 fusuliniformis (McCoy) = S. Carteri (Brady) (17) is the principal 

 constituent of enormous areas of limestone in Great Britain and on 

 the Continent (PI. 1, fig. 2). The upper Carboniferous limestone, 

 on the other hand, is in most regions of the world largely built up 

 of the shells of Fusulina, a perforate foraminifer belonging to 

 the family Nummulinidae. Other genera which are largely 

 concerned; in the formation of Carboniferous limestones are 

 'Endothyra\i^\. 1, fig. '6) and Archaediscus, while in this period 



