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 strie. 
Diam. .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. 
