FORAMINIFERA OF THE ATLANTIC OCEAN. 139 



Vaginulina spinigera — material examined. 



Genus FRONDICULARIA Defrance, 1824. 



Frondicularia Defbance (type, F. complanata Defrance), Diet. Sci. Nat., 

 vol. 32, 1824, p. 178. 



Description. — Test compressed, in the adult consisting of cham- 

 bers, elongate and narrow, running back on either side of the test; 

 wall vitreous, finely perforate; aperture single, either radiate or 

 surrounded with a lip which is usually cut in a radial manner; sur- 

 face smooth or ornamented with costae; microspheric specimens 

 with a coiled development in the earlier chambers; megalospheric 

 specimens without the coiled chambers as a rule. 



The genus Frondicularia is evidently derived from a coiled an- 

 cestry, such as CristcUarict. The microspheric forms invariably show 

 coiled chambers in the young, and were formerly placed under the 

 genus Flabellina. Megalospheric specimens of the same species 

 often show typical adult characters appearing directly after the pro- 

 loculum. 



Its geological history ranges from the Permian to the present. 

 It is particularly abundant in the Cretaceous. At the present time 

 large typical Frondicularia species are comparatively rare. There 

 is a development of it in the warmer waters of the western Atlantic, 

 and in tropical and subtropical waters of the Pacific at depths 



