88 



SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1921. 



waters of the. tropical and subtropical parts of 

 the Pacific and Indian oceans. As a fossil it is 

 also known from the Miocene of the Coastal 

 Plain of the United States, from the Calvert 

 formation of Chesapeake Beach. Md., and from 

 the Duplin marl of Mayesville, S. C. This 

 form thus represents a group which lived in this 

 region in early Oligocene time and persisted 

 into the Miocene but then apparently died out 

 here, though it continued in the Indo-Pacific 

 region, to which it may have migrated during 

 the Oligocene. 



Certain other species, such as Truncaiulina 

 hi/rainensis Cushman, n. sp., are evidently 

 characteristic of the Miocene and may not have 

 persisted later than that time. TnincatuJina 

 hj/raniensis is closely related to T. hasihba Cush- 

 man and T. concentrica Cushman, from the 

 Miocene of South Carolina and Florid::. 



LepidocycJinn sfipera (Conrad) is characteris- 

 tic of a group which so far as known is limited to 

 this horizon and not known elsewhere. L. supera 

 seems to be an index fossil of the Byram marl. 



RELATION OF BYRAM FAUNA TO FAUNAS OF 

 OTHER LOWER OLIGOCENE FORMATIONS. 



The foraminiferal faunas of the other divi- 

 sions of the lower Oligocene have not been 

 thorougUy studied except at the type stations. 

 Evidence is therefore incomplete as to the defi- 

 nite relationships of the several faunas. 

 Enough is known, however, to show that a 

 numbei- of the species of the Byram marl are 

 found also in the Mint Sjjring marl and a lesser 

 number in the Red Bluff clay, both of which lie 

 below the Byram marl in Mississippi. Some of 

 these species are also found in the Marianna 

 limestone of ^ilabama and Florida, but the 

 ecologic conditions of Florida and Mississippi 

 in early Oligocene time were evidently very 

 different, and that alone would account for a 

 considerable difference in the faunas. 



ECOLOGIC CONDITIONS UNDER WHICH THE 

 BYRAM MARL WAS DEPOSITED. 



From a comparison of tlu^ records for those 

 species which are found fossil in the marl at 

 Byram and also living in the Indo-Pacilic 

 region it is evident that the Byram marl was de- 

 posited in comparatively shallow water (10 to 

 25 fathoms). As nearly all these species occur 

 in the tropical and subtropical waters of the 

 Indo-Pacific, it would seem that the water at 

 Byram must have had at least subtropical 

 temperature (between 20° and 24° C). As the 



Miocene climate was evidently colder, espe- 

 cially along the Atlantic coast, this alone is 

 probably sufficient reason for the extinction 

 of those species which persisted in the general 

 region until that time. 



SPECIES INCLUDED. 



Figures are given of most of the species here 

 described. A closer study of the material has 

 shown how little is the variation of any par- 

 ticular species in this marl, and it may be 

 cjuestioned whether I am right in the specific 

 references of certain forms, such as those of 

 Polyinorphina. However, until a comparative 

 study of recent anil fossil material can be 

 made they may bc^st be left as at present. It 

 will undoubtedly become possible at some 

 future time to distinguish the fossil species of 

 our Coastal Plain and to divide them much 

 more closely and definitely. 



vSomething of tlie known distribution of the 

 species is given as well as full descriptions. A 

 list of the species is given 1)elow and is followed 

 by th(^ systematic prescntalit>n of ihr fauna. 



TextuUiriidae: 



Trxfiilaria agglutinans ])'(^rliigny. 



Toxtularia tnraiduhun Cushman. n. sp 



Textularia siil)haucrii Cushman, n. .sp. 



Tc'xtularia mississippiensis Cushman. n. sp. 



Toxtularia folium Parker and .lont'S. 



Boli\'ina amytjdalaeformis H. B. Brady. 



Boli\'ina nitida II. B. Brady. 



Boli\'ina rohusta H. B. Brady. 



Bolivina mis.sissippiensis Cushman. n. sp. 



Verneuilina spinulosa Reuss var. srlalirata Cushman, 

 n. var. 



Clavulina byramensis Cushman. n. sp. 



^'Ll■gulina. sp. 



Bulimina ovala ll'Orl)igny? 



Elu'enberginaglabrata Cushman. n. sp. 

 Lagenidae: 



Nodosaria sp. 



Nodosariasp.? 



Cristellaria sp. 



Vagimilina Ifgumcn (Linnaeus I li'Orhigny var. plegans 

 D'Orbigny? 



Polymorphina gibba IVOihigny. 



Polymorphinagiliba D'Orl>igny. fistulose form. 



PoljTuorphina regina H. B. Brady. Parker, and .Tones. 



Poljonorphina Iiyramensis Cushman, n. sp. 



Polymorphina problema D'Orbigny? 



Polymorphina amygdaloides (Reuss) Reuss. 



Uvigerina byramensis Cushman, n. sp. 

 Globigerinidae ; 



Gloliigeriua buUoides D'Orbigny. 



Globigerina triloba Reuss. 

 Rotaliidae: 



Spirillina sulidecorata Cushman, n. sp. 



Discorbis lijTamensis Cusihman. n. sp. 



Discorbis orldrularis (Terquemi Beithelin. 



