198 INVERTEBRATE PALAEONTOLOGY 



(B) PROTOZOA 



The outstanding features in the Foraminiferan fauna 

 of the Cainozoic era are the remarkable abundance, size 

 and elaboration of Nummulitids and Miliolids in the 

 earlier periods, and the overwhelming predominance of 

 Globigerinids in later and existing times. The coin-like 

 tests of Nummulites often attained diameters exceeding 

 two inches ; they were the chief limestone-builders in the 

 Mediterranean district during the Eocene and Oligocene. 

 Miliolids play a corresponding part in the construction 

 of the well-known Eocene "Calcaire grossier." Vast 

 numbers of small Nummulitids (Nummulind) and rela- 

 tively large Miliolids (Alveolind) occur in some of the 

 Upper Eocene clays of the Isle of Wight, but Foramini- 

 fera are never rock-formers in British Tertiary strata. 

 Globigerina is the most abundant constituent of foramini- 

 feral ooze in the late Tertiary and Holocene. 



Radiolaria are well represented in many districts, 

 and their remains, practically unaltered, are sometimes 

 sufficiently abundant to have an economic value. The 

 well-known " Barbados Earth," and the equally famous 

 "Tripoli Powder," are nothing more than deposits of 

 uncompacted Radiolarian ooze. They are used as 

 polishing powder and for dilution of explosives. Both 

 these deposits are of Miocene age, but the majority of 

 genera composing them are still living. Nasselaria 

 are considerably in excess of Spumellaria, and their 

 grotesque, but exquisite, tests are familiar to all micro- 

 scopists. 



(C) PORIFERA 



Remains of Sponges are rare in British Tertiary 

 deposits. The muddy and often estuarine conditions 

 prevalent in sedimentation areas were uncongenial to 



