GEOLOGICAL ANTIQUITY OF FORAMINIFERA. 479 



Foraminifera. The Foraminifera are widely distributed in exist- 

 ing seas, occur at all depths, and in all oceans. Their living sub- 

 stance, though sometimes yellow or red, is of a white-of-egg-like 

 texture, is termed sarcode, and secretes shells, which are mostly micro- 

 scopic, and in many types are perforated for the passage of retractile 

 threads termed " pseudopodia." The group is subdivided into three 

 sections ; first, the PORCELLANEA or Imperforata, which consists of 

 solid white shell tissue ; secondly, the ARENACIA, which are built up 

 of grains of sand and other particles blended with their calcareous 

 coating ; third, the HYALINA or Perforata, which comprises the great 

 majority of fossil forms. All three groups are closely connected by 

 intermediate types. 



The only Foraminifer yet determined in the Pre-Cambrian rocks 

 is the large incrusting Eozoon. There are none certainly identified 

 from the Cambrian rocks ; but with the Silurian strata we find the 

 existing genera Dentalina y Lagena, Nodosaria, and Textularia, which 

 all belong to the Hyaline section. The majority of Primary types 

 date from the Carboniferous period. Among such genera which still 

 survive are the porcellanous Cornuspira, the arenaceous Saccammina, 

 Lituola, and Trochominina, and the hyaline Spiroplecta, Valvulina, 

 Planorbulina, Pulvinulina, Calcarina, Amphistegina, and Nummu- 

 lites. Several of these types are at present imperfectly known in the 

 Secondary strata. Among genera which are peculiar to the Carbon- 



Fig. %j.Nummulit'.s (Lower Tertiary species). 



iferous period are Stacheia, Archcediscus, and Fusulina, which last is 

 also of Permian age. 



With the Trias other recent types come in, such as Miliola, 

 Nubecularia, Dactylopora, Webbina, Bulimina, Lingulina, Frondicu- 

 laria, Marginulina, Vaginulina, Cristettaria, Planularia, Flabellina, 

 Polymorphina, and Globigerina. 1 With the Lias appear the por- 

 cellanous Orbitolites and the Hyaline Orbulina. With the Oolites 

 come in Verneuilina and Spirillina ; the only new Ncocomian genus 

 is Operculina. The Upper Greensand introduces Patellina, while in 

 the Chalk the new forms all belong to the Hyaline group. They 

 comprise Spiroplecta, Chrysalidina, Allomorphma, Ramulina, Pullenia, 

 Sphceroidina, Discorbina, Cymballopora, Rotalia, and Polystomella. 

 The extinct genera of the Secondary period belong to the Arenaceous 



1 This genus has been quoted from Carboniferous rocks. 



