Planktonic Foraminiferal Families Hantkeninidae, Orbulinidae, 

 Globorotaliidae and Globotruncanidae 



By Hans M. Bolli, ^ Alfred R. Loeblich, Jr., and Helen Tappan 



Introduction 



DURING THE PAST 10 to 20 years there has been an 

 enormous increase in the recognition of the value of 

 the planktonic Foraminifera as stratigraphic index 

 fossUs. They form an excellent basis for precise 

 regional and world-wide correlation. Their dispersal 

 is world-wide, affected only by such environmental 

 factors as temperature and salinity. After death their 

 shells sink to the sea floor, regardless of whether the 

 bottom facies is abyssal, neritic, lagoonal, or reefal. 

 Furthermore, the advent and extinction of species 

 and even genera, from the Cretaceous to the Recent, 

 is so spaced that an excellent and exact zonation can 

 be based on their stratigraphic distribution. 



At the present time the value of the planktonic 

 Foraminifera for stratigraphic correlation is masked 

 by the incompleteness of our knowledge and especially 

 by the divergent views of different workers on questions 

 of taxonomic grouping. The basis for systematic 

 separation of planktonic Foraminifera has varied 

 greatly from author to author. Features used by one 

 specialist as being of specific value only are used by 

 others for generic and even family separations. The 

 wide limits allowed for a genus in some instances have 

 almost completely masked the true value of the plank- 

 tonic Foraminifera for stratigraphic correlation. A 

 critical examination of many species of widely varjdng 

 geographic and stratigraphic occurrence makes it 

 obvious that there are distinctive groups of species, 

 within a "genus" as previously known, that are quite 

 restricted in geologic range. Other species, attributed 

 to different "genera" may have identical ranges and 

 only minor distinctions for separation, and may even 

 intergrade. For these reasons the classification of the 

 planktonic Foraminifera definitely requires revision 

 on the generic level. 



Descriptions and illustrations in many publications, 

 especially early ones, are oftten too generalized, in- 

 accurate or incomplete for a precise species delineation. 

 Lack of care in the collection of samples and failure 

 to recognize reworking has in some instances given 

 exaggerated geologic ranges. In many instances a 

 disregard for the Rules of Nomenclature has caused 

 confusion. 



In order to revise the systematics of the planktonic 

 Foraminifera and to determine their exact stratigraphic 



ranges and the factors important in their geographic 

 distribution, a cooperative study of this group has 

 been undertaken by a nmnber of paleontologists in 

 both hemispheres. The present article is the first of 

 a series resulting from this project, and was undertaken 

 largely as a basis for future publications. All known 

 genera of the families Hantkeninidae, Orbulinidae, 

 Globorotaliidae and Globotnmcanidae have been re- 

 described on the basis of their type species, and the 

 best specimens obtainable of each of the type species 

 have been figured here. In many instances, both the 

 holotype of the type species and additional topotypes 

 or hypotypes have been figured, and for certain genera 

 additional species have also been included. Although 

 we have placed many previously described generic 

 names in synonymy, we have nervetheless figured the 

 type species designated for those nominal genera, so 

 that the record wiU be complete. 



A general discussion of the planktonic Foraminifera 

 is given here with remarks on their ecology, morphology 

 and terminology, evolutionary trends, and geologic 

 distribution. This is followed by the systematic por- 

 tion of the paper. 



In the present revision, a total of 56 generic names 

 are considered, of which 32 genera are recognized as 

 valid, including 5 proposed as new. Many of the 

 previously described genera are emended somewhat, 

 and recognized as valid on a basis distinct from that 

 originally proposed. Some are used in a more restricted 

 sense, thus becoming of greater stratigraphic value. 

 Others are considered somewhat more inclusive than 

 originally proposed, when neither valid structm-al dis- 

 tinctions nor differing geologic occurrence would uphold 

 a closer separation. 



Of the remaining generic names, 23 are here con- 

 sidered synonyms and suppressed. One name is a 

 homonym and had been earlier replaced by a valid 

 name, by the original author. Incidental to the generic 

 studies, 7 new species are also described. 



These 32 valid genera are placed in 4 families, with 

 7 subfamilies, of which 4 subfamilies are new. The 



' Arrangement of names alphabetical, no seniority Implied. Hans M. BolU, Trini- 

 dad oil Company, Ltd. (formerly Trinidad Leaseholds, Ltd.), Polnte-4-Plerre, 

 Trinidad, B. W. I.; Alfred R. LoebUch, Jr. (formerly associate curator of Invertebrate 

 paleontology, V. S. National Museum), California Research C!orp., La Habra, Calif.; 

 and Helen Tappan, Research Associate, Smithsonian Institution. 



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