6 E. HERON-ALLEN AND A. EARLAND ON THE FORAMINIFERA 



occur the first records of two genera, Amphistegi?ia and Nura- 

 mulites, which in later times were destined to play an important 

 part in the formation of the world's crust. 



The Permian and Permo-Carboniferous rocks show a decline 

 in the importance of the Foraminifera. Perhaps it would be 

 more correct to say that there is a falling off in the records of 

 those large and dominant types which marked the Carboniferous 

 period. Foraminifera of many different genera occur in the 

 Permo-Carboniferous rocks, but they are usually of compara- 

 tively small size, and so do not readily form a basis for rock 

 formation. But in New South Wales and Tasmania, Nubecularia, 

 which is the lowest type of imperforate foraminifer, forms a 

 principal constituent of some limestones (18) (PL 1, fig. 4). 



TheTrias yields no strata in which Foraminifera are the principal 

 constituent. Foraminifera occur in many horizons, but do not 

 constitute any large proportion of the fauna. Perhaps the 

 richest deposit is that described by Chapman (19) from Wedmore 

 in Somerset. 



Similarly in the Jurassic period, the Foraminifera, although 

 often varied and abundant, are not responsible for any important 

 proportion of the whole bulk of the formation. They are often 

 confined to limited zones, in which they occur in great abundance, 

 but the species are nearly all minute and completely masked as 

 to external appearance by other material. The most important 

 feature of this period, however, is the sudden bursting into active 

 existence of numerous hyaline types, principally Lagenidae, 

 hitherto more or less unknown. They occur in the clays of the 

 Lias of the Continent in enormous variety, passing insensibly 

 from one species into another, and the meticulous precision of 

 Terquem and others who have monographed these strata has 

 embarrassed the rhizopodist with a wealth of synonyms. 



Up to this period the arenaceous Foraminifera have not presented 

 any great diversity of forms, although, as we have seen, certain 

 genera (Saccammina, Endothyra, etc.), have played an important 

 part in building up strata. But Haeusler (20) (21) has de- 

 scribed a most interesting series of arenaceous types from a 

 sandy marl of Jurassic (Oxfordian) age in the Canton of Aargau 

 (Switzerland), which includes many genera now known to us 

 only from deep water. It is altogether one of the most pro- 

 nounced and characteristic rhizopodal faunas recorded in the 



