14 PALAEONTOLOGY. 



the carboniferous limestone of Eussia. The recent genera 

 Dentalina and Texhdaria are found in the magnesian lime- 

 stone ; Nodosqria, Cristellaria, and Rotcdia, in the lias. Fla- 

 bellina (fig. 2, 6) is peculiar to the chalk ; Orbitoides (fig. 2, 9) 

 to the chalk and tertiary series ; Ovulites (fig. 2, 10) is peculiar 

 to the eocene and Frondicidina to the miocene tertiaries; 

 Operculina, Orbitolites, and Alveolina appear first in the 

 tertiary, and are still living. Lituola (fig. 2, 7) occurs in the 

 chalk and chalk flints, and some species with chambers filled 

 by a chalky porous matter have been referred to a genus 

 Sjnrolma. Many of the cretaceous forarninifers contain a 

 brown colouring matter, which remains after the shell has 

 been dissolved with weak acid, and has been regarded as the 

 remains of the organic substance which once filled all the 

 ceils. 



The lower eocene beds in the " calcaire grossier," which 

 are employed at Paris as a building-stone, contain fora- 

 rninifers in such abundance that one may say the capital of 

 France is almost constructed of those minute and complex 

 shells. 



But it is in the middle eocene, or " nummulitic period," 

 that the Khizopods attained their greatest size, and played 

 their most important part. "Wherever limestones or calcare- 

 ous sands of this period are met with, these coin-shaped shells 

 abound, and literally form strata which in the aggregate 

 become mountain masses. The " nummulitic limestones are 

 found in Southern Europe, in Northern Africa, and in India ; 

 they also occur in Jamaica. The commonest form is the 

 true Nummidite (fig. 2, 8), which occurs in the building-stone 

 of the Great Pyramid. The Nummulites were evidently 

 sedentary organisms ; and in the large thin species, one side 

 is moulded to the inequalities of the sea-bed on which it 

 grew. 



Polycjjsti.nca\—Th.Q tertiary marls of Barbadoes afforded 



