244 THE FOEAMINIFEEA 



shallow water often in the neighbourhood of coral 

 reefs. Eocene to Becent. (Plate 13, figs. I, i, i'.) 



Genus Nummulites, Lamaeck. 



Test lenticular or complanate, piano-spiral, regu- 

 lar. Segments equitant, the alar prolongations of 

 each convolution completely enclosing the previous 

 whorls. Aperture simple, close to the periphery of 

 the previous convolution. Supplemental skeleton 

 provided with a complex canal system. Carbonife- 

 rous, (?) Jurassic, Tertiari/, and Becent. 



The palaeozoic specimens of this genus are small 

 but characteristic ; they were found in the Carboni- 

 ferous limestone of Belgium. Nummulites is, how- 

 ever, peculiarly a Tertiary form, and was abundant in 

 Eocene and Oligocene times, especially in the 

 former. The recent specimens are not far removed 

 in structure from Operculina and Ami^liistegina. 



Example. — N. elegans, Sower by sp. (Nummu- 

 laria), ' Mineral Conchology,' vol. vi. 1826, p. 76, 

 pi. xxxviii. fig. 2 ; Eupert Jones, ' Quart. Journ. 

 Geol. Soc' vol. xliii. 1887, p. 132, pi. xi. figs. 1-9. 



This species, with its thin complanate test, is 

 found in abundance in certain horizons of the 

 Barton Beds of the Isle of Wight and Hampshire. 

 (Plate 14, figs. A, a, B.) 



Genus AssiJiiia, D'Oebigny. 



Test complanate, structure similar to that of 

 Nummulites, but the alar extensions of the chamber- 

 walls thin and closely superimposed, so that the 



