32 BULLETIN 104, UNITED STATES NATIONAL MUSEUM 



Genoholotype. — AmpMstegina cumingii W. B. Carpenter. 



Test lenticular and involute in the young, bilaterally symmetrical, 

 in the adult with a broadly flaring complanate border; chambers 

 simple; aperture at the base of the apertural face, median. 



Late Tertiary and Recent. Indo-Pacific. 



Genus OPERCULINA d'Orbigny, 1826 



Operculina d'Orbigny, Ann. Sci. Nat., vol. 7, 1826, p. 281. 



Nautilus (part) of Authors. 



Lenticulites (part) Deprance, 1822. 



Amphistegina (part) d'Orbigny, 1826. 



Nonionina (part) Williamson, 1852. 



Nummulina (part) Parker and Jones, 1865. 



Genotype, by designation. — Operculina complanata d'Orbigny. 



Test bilaterally symmetrical, planispiral, complanate, usually all the 

 coils visible from the exterior, eariier coils sometimes involute; wall 

 calcareous, perforate, smooth or ornamented with bosses; aperture 

 single, at the base of the apertural face, median. 



Lower Cretaceous to Recent. 



There are many records, especially from the North Atlantic, referred 

 to "Operculina ammonoides (Gronovius)." This small species is not 

 an Operculina, but belongs with the Anomalinidae, and should be 

 known as Planulina ammonoides (Gronovius) and will be taken up in 

 the next part of this work. 



True Operculinas are apparently not found in the Atlantic although 

 they occurred in the West Indian region abundantly in the Upper 

 Eocene and less so in the Oligocene. They are still persistent and 

 reach large size in the warm shallow waters of the Pacific. 



Genus HETEROSTEGINA d'Orbigny, 1826 



Heterostegina d'Orbigny, Ann. Sci. Nat., vol. 7, 1826, p. 305. — Cushman, 

 Special Publ. No. 1, Cushman Lab. Foram. Res., 1928, p. 213. 



Genotype, by designation. — Heterostegina depressa d'Orbigny. 



Test similar to Operculina, the early chambers simple, later ones 

 divided into chamberlets; aperture consisting of a row of rounded 

 openings on the narrow apertural face. 



Eocene to Recent. 



This genus reached its climax in the Upper Eocene, and is now 

 represented in the Atlantic only in the West Indian region, and there 

 by but a single species. It is represented in the tropical Pacific by 

 large fine species which have still persisted and find their natural 

 habitat in warm waters of less than 30 fathoms. 



