192 CONTRIBUTIONS 



O. discoidea. Plate 6. Fig. 205. 



Description. Orbitolites cellular and very slightly con 

 vex above, minutely porous, radiate and slightly con 

 cave below ; cells hexagonal ; pores very minute and 

 placed between the radiating striae. 



Diara. .3, Height .1, of an inch. 



The segment is a magnified view. 



Observations- This species differs very much from the 

 above- It is flatter and larger, and in the arrangement 

 of the cells and pores differs altogether. The apex of my 

 specimen (the only one I have seen) is disposed to be 

 mammillary. The grain of sand mentioned in the Lunu- 

 lites is not observable in this species. 



A single species only of this genus seems to have been 

 observed in England. M. Mantell in his Geology of Sus 

 sex, mentions the lenticulata (Lamarck) as existing in the 

 Chalk. Lamarck describes six species, one of which is 

 recent. The macroptera (Lamarck) is mentioned by 

 Goldfuss, who describes this species as being found only 

 in the Calcaire Grossiere of Paris. In this country the 

 genus has not been before observed. 



