VOLUME 87, NUMBER 321 - COMA zom, MARCH 27, 1985 Miocene Diatoms from the Hawthorn Formation, | Thomas County, Georgia by George W. Andrews and William H. Abbott Paleontological Research Institution 1259 Trumansburg Road Ithaca, New York, 14850 U.S.A. PALEONTOLOGICAL RESEARCH INSTITUTION Officers PRESIDEN en ns UT OS Ru ee Une WILLIAM A. OLIVER, JR. VEC Her RESIDENTES Se DU ee er Aci, WILLIAM P. S. VENTRESS EE HENRY W. THEISEN EREASCRERO RR CUL E OU ee ee ROBERT E. TERWILLEGAR ASSISTANT: LE REASURER sige in bo vei ER AE ES JOHN L. CISNE REC TOR es ee eee PETER R. HOOVER EEC COU NSE oie go ry eee ee e E M en HENRY W. THEISEN Trustees BRUCE M. BELL (to 6/30/87) WILLIAM A. OLIVER, JR. (to 6/30/86) RICHARD E. BYRD (to 6/30/86) JOHN POJETA, JR. (to 6/30/85) JOHN L. CISNE (to 6/30/85) JAMES E. SORAUF (to 6/30/85) J. THOMAS DUTRO, JR. (to 6/30/87) ROBERT E. TERWILLEGAR (to 6/30/87) LEE B. GIBSON (to 6/30/86) HENRY W. THEISEN (to 6/30/86) HARRY A. 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Hoover Director Paleontological Research Institution 1259 Trumansburg Road Ithaca, New York 14850 U.S.A. 607-273-6623 k ulletins erica? alcontology VOLUME 87, NUMBER 321 MARCH 27, 1985 Miocene Diatoms from the Hawthorn Formation, Thomas County, Georgia by George W. Andrews and William H. Abbott Paleontological Research Institution l 1259 Trumansburg Road Ithaca, New York, 14850 U.S.A. Library of Congress Card Number: 85-60613 Printed in the United States of America Allen Press, Inc. Lawrence, KS 66044 U.S.A. CONTENTS Page Abstract. EE, Dno Pg peur UON E eee ROS tee M LEM a 57 rodi COR E SS O EE 57 COW IEC Ee UM a e o cr eet eee 58 IEOCALIONLO DIS LO Ri RM E E Eeer OA ee 59 ME EN EER. O ne O M ELE ie O ce 59 Previous Daron Work res A e EE ENEE 59 Summary OINVÉSU SAN ONE Me Pe a e ne 60 by atom A SSCMDIARE SA in a EA E Eh E 60 Correlation Miocene Section.in: Maryland Capra ankamen EE E Ne TE fe ede d 62 Hawthom SEET EE land oU Eee dE ee E IM o 63 INonmarıne Diatomrässemblagerte aa us adie e Ne PR M M le cas 63 Age of Diatom FAS Tall} Ech eee daar N E hr TN AUG E M EIU TN E IE 64 Palegeco 02 eR. EE A COREL RARE IER T NA EE 64 Systematic Paleontology Thtfodüctionee armen le a DT Ae SEA os PL ge LOC dr pastum qu Pie Ee ce 65 Philosophicalk@onsiderations.. o o is e eek nd LN Lc LH Td 65 tata Cobo] Bot e M AS c MEM M MEM TI TRI RN M Ea mE RU 68 NOM AT D TO SE MEC EMERICUS 88 Reference Gl te cdi Ma DECIR PME QUE AT RE A LS oem AOA Nm I em ee Eien A C Em Ceara ine gee 91 Bliites ic wi nr en Keimen AS. DIR FTD NA C erben P Toc 95 LIST OF ILLUSTRATIONS Text-figure Page 1. Index map showing location of diatom locality in Thomas County, Georgia and its relationship to the regional paleogeography.. 58 2. Isopach map of upper Oligocene and Miocene sedimentary rocks, showing major depocenters ............................... 59 3. Location of the O1-Dri Corporation fuller s:earth mine near Ochlookuee; Georgia: ee dore sehe 59 4. Stratigraphic position, associated lithology, and inferred paleoecology of diatomaceous samples of the Coosawhatchie equivalent Dens te ie Olle ne OO DOTE Olly TEE SCALE = tie com cre rene ecm EIE C ren nn ns Cerda eet ee mee 61 LIST OF TABLES Table Page l ROO He uem Of marme diaron Tasa docu ee aus df EE foldout inside back cover 2. Relative frequency of occurrence of nonmarine diatom taxa in the Coosawhatchie equivalent beds, Thomas County, Georgia ... 62 Additional taxa of marine diatoms observed and identified by W. H. Abbott in samples supplied by C. E. Weaver ............ 63 3: MIOCENE DIATOMS FROM THE HAWTHORN FORMATION, THOMAS COUNTY, GEORGIA By GEORGE W. ANDREWS WILLIAM H. ABBOTT U.S. Geological Survey Mobil Exploration and Producing Services 970 National Center Post Office Box 900 Reston, VA 22092, U.S.A. Dallas, TX 75221, U.S.A. ABSTRACT Diatomaceous sediments of the Hawthorn Formation occur in commercially mined fuller’s earth and related deposits near Ochlocknee, Thomas County, southwestern Georgia. These sedimentary rocks were deposited in the Gulf Trough, a relatively narrow linear area of subsidence connecting the Applachicola Embayment and the Southeast Georgia Embayment during a part of Tertiary time. Eighty-four taxa of marine diatoms have been identified, including one new species, Actinoptychus aequalis. These diatoms indicate deposition in a shallow marine environment. An intercalated nonmarine diatom assemblage has been found near the top of the section and contains a mixture of brackish- and freshwater diatoms. The marine diatom assemblage of this deposit of the Hawthorn Formation is correlative with approximately the lower part of Miocene Lithologic Unit 14 of the Calvert Formation in the Chesapeake Bay Region of Maryland; thus, it is early middle Miocene in age. INTRODUCTION Extensive deposits of fuller’s earth in the Hawthorn Formation in southwestern Georgia and northern Flor- ida have been commercially exploited since 1895 (Pat- terson, 1974, p. 1). The term “fuller’s earth” originally referred to any fine-grained earthy material used in fulling and cleaning wool, usage that dates back to ancient time. The term is now generally applied to highly absorbent clays that have a wide variety of in- dustrial and domestic uses. A commercial deposit of fuller's earth, consisting principally of the minerals pal- ygorskite, sepiolite, and montmorillonite, is currently being mined by the Oil-Dri Corporation of America near Ochlocknee, Georgia. The fuller's earth and the overburden of this mine contain fossil marine and non- marine diatom assemblages that provide data on the age and paleoecology of the Hawthorn Formation in Southwestern Georgia. The name “Hawthorne beds” was originally applied to deposits of phosphatic sandstone, sand, ferruginous gravel, and greenish clay of Alachua County, Florida, by Dall in Dall and Harris (1892, p. 107). It has since been applied to a variety of Tertiary deposits scattered through Alabama, Georgia, Florida and South Caro- lina. Puri and Vernon (1964, p. 145) commented co- gently on the formation as follows: “The Hawthorn Formation perhaps is the most misunderstood for- mational unit in the southeastern United States. It has been the dumping ground for alluvial, terrestrial, ma- rine, deltaic and prodeltaic beds of diverse lithologic units in Florida and Georgia, that are stratigraphic equivalents of the Alum Bluff Stage.” Patterson (1974, pp. 10-11) outlined paleontological work that has been done on the Hawthorn Formation and concluded “‘that it is neither the youngest nor the oldest of the Miocene formations in the Coastal Plain and that the middle Miocene is a realistic age assignment for this forma- tion.” Abbott and Huddlestun (1980) revised the Haw- thorn Formation to group status and raised the former members of the Hawthorn to formational rank. The uppermost formation in their Hawthorn Group is the Coosawhatchie Clay, described initially by Johnson and Geyer (1965) as the Coosawhatchie Clay Member of the Hawthorn Formation. The fuller’s earth deposits of Thomas County, Georgia are considered to be cor- relative with the Coosawhatchie Clay by Paul Hud- dlestun, Georgia Geological Survey (written commun., 1981), but he does not believe that the field evidence justifies an unqualified assignment of these deposits to the Coosawhatchie Clay. We shall, therefore, formally consider these diatomaceous deposits of Thomas County, Georgia as a part of the Hawthorn Formation. The establishment of the “Coosawhatchie Clay” as a formation of the “Hawthorn Group” has not yet been formally published, nor has the Coosawhatchie been mapped in Thomas County. We shall, therefore, refer to the deposits under consideration in this report as “Coosawhatchie equivalent beds” in a strictly informal sense. The location of the deposit of the Coosawhatchie equivalent beds studied for this report is shown in the index map (Text-fig. 1). Ochlocknee, Georgia is in northwestern Thomas County, a southwestern Georgia county bordering on Florida. An elongate structural trough filled with Miocene sedimentary rocks trends northeastward through this part of Thomas County and adjacent counties of Georgia and Florida. This 58 BULLETIN 321 trough was originally recognized by Johnson (1892) and was included in what he termed the **Chattahoo- chee embayment.” This same structural feature has also been included in the “Apalachicola embayment” and the “‘southwest Georgia basin” by others (Patter- son, 1974, p. 6). Part of this embayment was named the “Gulf Trough of Georgia” by Herrick and Vorhis (1963, p. 55, figs. 2, 3) and modified to “Gulf Trough” by Hendry and Sproul (1966, p. 97). In this report, we follow Patterson (1974, p. 6) in using the term “Gulf Trough” to denote the elongate Miocene depocenter northeast of the Apalachicola Embayment in south- western Georgia. Locations of the principal structural features of the region are shown in Text-figure 1. The position of the Gulf Trough as a linear structural basin connecting the Southeast Georgia Embayment that opens to the Atlantic Ocean and the Appalachicola Embayment that opens to the Gulf of Mexico is delin- eated in Text-figure 2, an isopach map of upper Oli- gocene and Miocene sedimentary rocks in the region. Patterson (1974, p. 7) has suggested that the Gulf Trough was probably a strait separating peninsular Florida from the mainland during Oligocene and much of Miocene time. Probably no open-water connection existed through the Gulf Trough between the Gulf of Mexico and the Southeast Georgia Embayment of Toulmin (1955) during deposition of the Coosa- whatchie equivalent beds. Weaver and Beck (1977, pp. 15-16) have suggested that the Gulf Trough was open to the Atlantic waters of the Southeast Georgia Em- bayment and that it was either closed or greatly re- stricted toward the southwest during the time of de- position of the Coosawhatchie equivalent beds of Thomas County, Georgia. Paul Huddlestun (written commun., 1981) has indicated that the Gulf Trough and the Southeast Georgia Embayment were almost certainly connected during early and middle Miocene time when inner shelf and upper estuarine deposits were laid down. He believes that the Gulf Trough and the Southeast Georgia Embayment were permanently separated by the end of Coosawhatchie time. The Coosawhatchie equivalent beds studied for this report were apparently deposited in waters derived from the Atlantic Ocean basin, rather than waters derived from the Gulf of Mexico. The nonmarine bed herein de- scribed probably was deposited during a relatively short-lived isolation of the Gulf Trough from free ac- cess to Atlantic waters and may perhaps be a precursor of its final separation from Atlantic waters. ACKNOWLEDGMENTS A sample of fuller’s earth from Thomas County, Georgia, was sent to the U. S. Geological Survey dia- tom laboratory, Washington, DC, by L. Ray Gremil- lion in 1963. Scanning electron micrographs were made of diatoms from this sample, because of their superior preservation. Charles E. Weaver, Department of Ge- ology, Georgia Institute of Technology, Atlanta, Geor- gia, supplied a suite of samples and stratigraphic in- formation on the Oil-Dri mine to W. H. Abbott. S. H. Patterson, U. S. Geological Survey, Reston, Virginia, and B. F. Buie, Department of Geology, Florida State University, Tallahassee, Florida, were our leaders on the Field Conference on Kaolin and Fuller’s Earth held in November 1974. John L. Stone, Washington, DC, prepared slides in a high-index mounting medium and assisted in identification of specimens. John A. Barron, U. S. Geological Survey, Menlo Park, California, Wil- liam C. Cornell, University of Texas at El Paso, El Paso, Texas, Paul F. Huddlestun, Georgia Geological Survey, Atlanta, Georgia, and J. P. Bradbury, U. S. Geological Survey, Denver, Colorado, have critically reviewed the manuscript. Suggestions made by Hud- dlestun and Bradbury have been incorporated into the aS b | e = see SOUTH CAROLINA ` \ N ^ | GEORGIA 1 \ H ^ ALABAMA) SOUTHEAST ( GEORGIA be DIATOM EMBAYMENT x LOCALITY & o o E--— =-= — OCALA UPLIFT SUWANNEE UPLIFT o 100 200 MILES 1 T T 100 200 KILOMETERS Qa- oi of? 1 85°W Text-figure 1.—Index map showing location of diatom locality in Thomas County, Georgia, and its relationship to the regional pa- leogeography. MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 59 report. The kind assistance of all mentioned above in the preparation of this report is deeply appreciated. LOCATION OF DEPOSIT The diatomaceous samples studied for this report were obtained from the Oil-Dri Corporation of Amer- ica fuller’s earth mine (formerly the Cairo Production Company mine), approximately 3.2 km (2 mi) north- west of Ochlocknee in northwest Thomas County, Georgia. The mine is shown as a group of “clay pits" near the north edge of the center of the U. S. Geological Survey (USGS) Ochlocknee, Georgia 7/2’ quadrangle, part of which is herein reproduced as Text-figure 3. 0 100 MILES ore | E TRS TET ART 0 100 KILOMETERS ENT ALABAMA FLORIDA Text-figure 2.—Isopach map of upper Oligocene and Miocene sedimentary rocks, showing major depocenters. Redrawn from Weaver and Beck (1977, fig. 2). BM 240 ZN \ de Ochlocknee 1 A ga À The E? | I E SS St = CONTOUR INTERVAL 10 FEET Text-figure 3.— Location of the Oil-Dri Corporation fuller’s earth mine near Ochlocknee, Georgia. Base from U.S.G.S. Ochlocknee, Georgia 7’ quadrangle. The location of the Oil-Dri Corporation mine has been published by Patterson and Buie (1974, pp. 42- 43) in the guidebook to the Field Conference on Kaolin and Fuller’s Earth. STRATIGRAPHY OF DEPOSIT The stratigraphy, lithology, and mineralogy of the Coosawhatchie equivalent beds in the Oil-Dri Cor- poration of America fuller’s earth mine near Ochlock- nee, Georgia have been described by Patterson (1974), Patterson and Buie (1974), and Weaver and Beck (1977). A measured stratigraphic section in the mine was published by Patterson (1974, pp. 36-37). Greatly simplified, the section consists of: (1) a lower deposit of commercial fuller’s earth, approx. 7.3 m (24 ft) thick consisting of light-gray, massive, tough, jointed clay and a few thin sand-clay-pebble beds; (2) the over- burden, approx. 11.9 m (39 ft) of interbedded pale- yellow soft plastic clays and light-gray clayey sands. The stratigraphic levels, associated lithology, and in- ferred paleoecology of diatomaceous samples studied for this report are shown in Text-figure 4. According to Weaver and Beck (1977), the basal clay of the fuller’s earth deposit is composed of approxi- mately 50% palygorskite and sepiolite and 50% montmorillonite, the montmorillonite and kaolinite increasing toward the top. In addition to quartz and Na- and K-feldspar, the fuller’s earth contains phos- phate and clay grains, sponge spicules, silicoflagellates, and ebridians as well as diatoms. From the overburden sediments, Weaver and Beck (1977) reported 90% montmorillonite and 10% kaolinite in the basal clays, kaolinite becoming dominant 3 m below the surface. Quartz, K-feldspar, biotite, and muscovite occur in the sands of the overburden. The correlation between the Weaver samples and the USGS diatom localities may not be exact. The compilation of Text-figure 4 was made by consider- ation of the stratigraphic section of Weaver and Beck (1977, text-fig. 54), showing the collection levels of the Weaver samples, the stratigraphic section of Patterson (1974, pp. 36-37), and our personal observations in the field. This compilation has been made carefully, however, and we believe that it reflects with reasonable accuracy the stratigraphic positions of the two sets of samples studied for diatoms. PREVIOUS DIATOM WORK Although the presence of diatoms in the fuller’s earth and associated strata of the Coosawhatchie equivalent beds in Thomas County, Georgia, was doubtlessly not- ed upon the first microscopic examination of these deposits, no systematic study of the diatoms was re- ported until 1965. A clay sample from the Cairo Pro- 60 BULLETIN 321 duction Company Mine near Ochlocknee, Georgia (the Oil-Dri Corporation of America mine of this report), was submitted by Gremillion (1965, pp. 44-45) for examination to Taro Kanaya, then at Tohoku Uni- versity, Sendai, Japan. Kanaya identified 19 diatom taxa, all of which he regarded as marine. He suggested correlation with the Calvert Formation of Maryland, which he considered to be middle Miocene in age. Examination of Kanaya’s species list indicates that he most probably examined a sample from the lower ma- rine section studied in this report. Although the strati- graphic ranges of many species are now better under- stood and new stratigraphically significant diatom taxa have been defined, Kanaya’s conclusions in no way conflict with this report. We can, however, now date this deposit more precisely by diatoms than could have been done in 1965. Weaver and Beck (1977, pp. 107-110) published a list of diatom species determined by W. H. Abbott from the Cairo Production Company mine (Oil-Dri Corporation of America mine of this report). This list was a composite of several samples submitted by C. E. Weaver to W. H. Abbott and listed 51 taxa of dia- toms. This study has been refined and is superseded by the present report, and the revised data are herein incorporated. SUMMARY OF INVESTIGATION Two sequential suites of diatomaceous samples from the Oil-Dri Corporation mine were studied for this report: (1) a sequence of nine samples, at irregular in- tervals, taken by C. E. Weaver and presented to Abbott for study; (2) a sequence of nine samples, mostly at 1 m (3 ft) intervals, taken jointly by Abbott and Andrews during the Field Conference on Kaolin and Fuller’s Earth on November 16, 1974. All the Weaver samples were studied in detail by Abbott; sample FE 100 was studied in detail by John Stone; samples FE 100, FE 106, FE 109, and FE 110 were studied in detail by Andrews to supplement those collected personally. The samples collected by Abbott and Andrews in 1974 were studied by both. Slides and photographs were ex- changed on a regular basis in order to prepare as com- plete a taxonomic treatment as possible. In the prep- aration of this report, the two writers were jointly responsible for the stratigraphic and paleoecologic treatment as well as for the regional correlation. Al- though Andrews was primarily responsible for the taxonomic treatment, taxa observed only by Abbott have been incorporated into the report. Andrews has assumed sole responsibility for any revisions of no- menclature or descriptions of new species. DIATOM ASSEMBLAGES Table 1 shows the distribution of diatom taxa in the strata exposed in the Oil-Dri mine. We will consider first the diatoms from the lower marine section and the upper marine bed (Text-fig. 4); the diatoms of the nonmarine bed will be considered subsequently. The compilation of Table 1 posed certain problems in that the writers, of necessity, had to work separately on the samples and because the samples came from two dif- ferent sources—from C. E. Weaver, and from our own collections. We dare not claim 0.3 to 0.6 m (1 to 2 ft) accuracy in correlation of the Weaver samples with those personally collected. Therefore, in Table 1 we have indicated only those marine taxa observed by Andrews or by both writers at the appropriate levels. Those taxa observed only by Abbott in the Weaver samples have been placed in Table 3, a supplemental list at the end of this section. This placement in no way should be construed to denigrate the importance of these taxa; they are included in the section on sys- tematic paleontology. It has only been necessary be- cause of doubt of the exact stratigraphic correlation between the two suites of studied samples and possible differences in frequency estimates between the writers. The diatom assemblage of the lower marine section is remarkably consistent throughout the fuller’s earth deposit and on up into the overburden. The uppermost sample (USGS diatom locality 6469, depth 8.8 m [29 ft]), although it shows obvious floral similarity to the lower strata, is distinctly different in that it is domi- nated by a single species, Actinoptychus aequalis, n. sp. The other samples show relatively little variation in diatom content, other than those expected in sam- pling. One possible exception is the sample at the 43 ft level (Weaver sample FE 104) in which Abbott ob- served a slightly larger assemblage of marine diatoms than at any other level. This may perhaps be the result of either more normal marine depositional conditions or fortuitous preservation. The diatom assemblages of the lower marine section, considered as a whole, but excepting the uppermost sample, seem to be relatively normal marine Miocene diatom assemblages. They are dominated by such species as Paralia sulcata (Ehrenberg, 1838), P. sulcata var. coronata (Ehrenberg, 1845c), and Melosira westii Smith, 1856, usually abundant in the Miocene strata of the southeastern United States. They have a rela- tively high component of benthic marine diatoms, sug- gesting deposition in relatively shallow marine waters. The assemblages show somewhat fewer species than one might expect in this region. We have listed 86 marine taxa in Table 1, whereas in the Coosawhatchie Clay Member of the Hawthorn Formation of eastern South Carolina and Georgia we observed 111 taxa (Ab- | | | | | | | | MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 61 | SAMPLE USGS | DEPTH IN | WEAVER | METERS DIATOM LITHOLOGY PALEOCOLOGY | SAMPLES prp | | (FEET) | 0 | 3 (10)- VERBURDEN- ii pea elle diese diag We BE PTE 2 UPPER MARINE BED pale-yellow soft apo — FE 109- | ma O. 1 adia plastic clay with inter] NONMARINE BED bedded light gray clayey sand a on 9,1 (aero 6469 - | FE 106-] | 12.2 (40) FE 105- LOWER | GE ee MARINE | FE 1034 6467- | gage | COMMERCIAL | EE d OMM SECTION 15.2 (50)- : (50) 6465-1 FULLER'S EARTH | EE pora 6464-1 light gray massive, | 6463- tough, jointed clay | 18.3 (60)4 FE 100- 6462 with a few thin sand- | 64614 clay- pebble beds ME tapa Ses inca ats md ind | 21.3 (70) Text-figure 4.—Stratigraphic position, associated lithology, and inferred paleoecology of diatomaceous samples of the Coosawhatchie / equivalent beds in the Oil-Dri Corporation fuller's earth mine. Sample depth is measured from a surface elevation of approximately 85.3 m (280 ft), the level of the adjacent upland shown on the U.S.G.S. Ochlocknee, Georgia 7'^' quadrangle map. The “Weaver samples" were submitted by C. E. Weaver to Abbott for examination. The “USGS diatom localities” indicate samples collected in the field by the writers in 1974. 62 BULLETIN 321 bott and Andrews, 1979). This may result more from poor preservation than from an initially restricted as- semblage. Under the light microscope many of the diatoms appear to be reasonably well preserved, but most show varying degrees of corrosion and etching under the scanning electron microscope. Patterson (1974, p. 11) has reported the occurrence of opal in the Coosawhatchie Clay. We found that it was difficult to disaggregate the fuller’s earth in order to free the diatoms for study, and lack of response to chemical treatment indicated siliceous cementation. This ce- mentation is, of course, a characteristic that makes the fuller’s earth commercially desirable, in that it does not readily disintegrate. Solution of silica probably has reduced the diatom assemblage in quality of preser- vation as well as in the quantity of specimens and variety of taxa. The uppermost diatomaceous level of the lower ma- rine section (USGS diatom locality 6469, 39 ft level) is distinct from the rest of the section. It has relatively few taxa and is dominated by Actinoptychus aequalis, n. sp. It shows affinities for the assemblage in the upper marine bed, which also has relatively few taxa and is dominated by A. aequalis. These levels seem affected by specialized ecologic conditions, which are discussed elsewhere in this paper. The nonmarine diatom assemblage (Weaver sample FE 109) includes 16 taxa listed separately in Table 2. This assemblage, relatively sparse both in numbers of taxa and of specimens, includes two distinct groups of diatoms: (1) brackish-water taxa known from modern environments, which are numerically more abundant; and (2) freshwater taxa, many of which are known from Miocene rocks of the midcontinent region of the United States. Again, one cannot be certain what the original assemblage may have contained, for the preservation of this assemblage is relatively poor. CORRELATION MIOCENE SECTION IN MARYLAND The Coosawhatchie equivalent beds, as exposed in the Oil-Dri Corporation fuller’s earth mine, appear to correlate with a part of the Calvert Formation of Mary- land on the basis of marine diatoms. Marker diatoms of the Calvert and Choptank Formations along Ches- apeake Bay have been studied by Andrews (1978), and a diatom zonation has been proposed for these depos- its. Abbott (1978) has also established a diatom zo- nation for the Atlantic margin, which, though differing in details, does not disagree substantially with that of Andrews (1978). Abbott’s zonation was based on ma- terials from the entire Atlantic coastal region of the southeastern United States and primarily on offshore deposits. Andrews’ zonation was based on materials Table 2.—Relative frequency of occurrence of nonmarine diatom taxa in the Coosawhatchie equivalent beds, Thomas County, Geor- gia. Estimated relative frequency under an 18 mm cover glass viewed at x 250 is defined as follows: A = abundant (at least one specimen in all fields of view); C = common (one specimen in many, but not all, fields of view); F = frequent (several specimens observed on slide but seen only in a few fields of view); R = rare (about | or 2 specimens observed on a slide). NONMARINE ASSEMBLAGE SAMPLE NUMBER Poteet OSs coca lea Glue: AE EI Achnanthes hungarica bu Caloneis westi Eunotia parallela Eunotia pectinalis Eunotia pectinalis var, minor Gomphonema affine var. insigne Gyrosigma aff, G. spencerii Melosira juergensi Navicula aff. N. radiosa Nitzschia hybrida Nitzschia tryblionella var: victoriae Pinnularia brevicostata Pinnularia fusana Pinnularia aff. P. microstauron GR a esmo b cH re as RO o aa sc tho ry | Spp Ca Stauroneis salina from Maryland from a more nearshore section of the Miocene deposits, but it recognizes that the principles derived might be applicable farther afield. Neither zo- nation has been previously applied to Miocene depos- its marginal to the Gulf of Mexico. The Coosawhatchie equivalent beds of Thomas County, Georgia, contain the following marine marker diatoms in common with the Maryland section: Actinoptychus marylandicus Andrews, 1976 A. thumii (Schmidt) Hanna, 1932 A. virginicus (Grunow) Andrews, 1976 Delphineis angustata (Pantocsek) Andrews, 1975 D. novaecaesaraea (Kain and Schultze) Andrews, 1977 D. penelliptica Andrews, 1977 Rhaphoneis adamantea Andrews, 1978 R. elegans (Pantocsek and Grunow) Hanna, 1932 R. fusiformis Andrews, 1978 R. magnapunctata Andrews, 1978 R. parilis Hanna, 1932 These marine diatoms suggest that the Coosa- whatchie equivalent beds correlate with the upper part of East Coast Diatom Zone (ECDZ) 4 (the Rhaphoneis | | | MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 63 Table 3.—Additional taxa of marine diatoms observed and iden- tified by W. H. Abbott in samples supplied by C. E. Weaver. Diploneis bombus Hemiaulus ambiguus H. polymorphus Rhizosolenia styliformis Rossiella praepaleacea Sceptroneis grandis Stephanopyxis corona S. lineata Synedra jouseana Trochosira spinosa Xanthiopyxis spp. Actinocyclus ingens Actinoptychus virginicus Anaulus birostratus Coscinodiscus asteromphalus C. decrescens C. gigas var. diorama C. marginatus C. stellaris C. vetustissimus Debya insignis Denticulopsis nicobarica parilis Partial Range Zone of Andrews, 1978) and with Atlantic Margin Siliceous Microfossil Zone (AMSMZ) IV (the Delphineis penelliptica Partial Range Zone of Abbott, 1978). These beds contain two diatom species — Actinoptychus thumii and Rhaphoneis elegans—that were observed only in the lower part of Miocene Lith- ologic Unit (MLU) 14 of the Calvert Formation by Andrews (1978). This suggests a fairly precise corre- lation ofthe Coosawhatchie equivalent beds with lower MLU 14, but, until stratigraphic ranges of marine dia- toms are more thoroughly understood, such precision must be accepted with caution. In any event, these beds can be no younger than ECDZ 4, for the upper limit of that zone is defined on the last occurrence of Rha- phoneis magnapunctata. Of the 11 marker diatoms listed, nine agree with this correlation completely. Rhaphoneis adamantea was last reported in the Maryland section at a slightly lower level in ECDZ 4, in the upper part of MLU 13. How- ever, this discrepancy is relatively small, and R. ada- mantea is closely related to (and possibly a short vari- ant of) R. magnapunctata, which ranges to the top of ECDZ 4. Probably, R. adamantea was by chance not observed at this stratigraphic level in the Maryland study. The only really vexing discrepancy is in the occurrence of Rhaphoneis fusiformis in the Coosa- whatchie equivalent beds. This was recorded from about the middle of ECDZ 2 to about the middle of ECDZ 3 in the Calvert Formation of Maryland. R. Jusiformis was never common in the Calvert Forma- tion, so perhaps its range is greater than was observed. A more detailed study might indicate that the forms identified as R. fusiformis from the two areas are not conspecific. In all, the correlation between the marine diatoms of the Coosawhatchie herein studied with ECDZ 4 in the Calvert Formation is substantial and is quite remarkable, considering their wide geographic separation. HAWTHORN FORMATION OF THE RIDGELAND TROUGH The marine diatom assemblage of the Coosawhat- chie Clay Member of the Hawthorn Formation of the Ridgeland Trough was previously described by Abbott and Andrews (1979). The Coosawhatchie was origi- nally named from beds exposed in the Ridgeland Trough of the East Georgia Basin in southern South Carolina and adjacent areas of Georgia. The Coosa- whatchie diatoms of the Ridgeland Trough were cor- related with those of ECDZ 6 (Rhaphoneis gemmifera Range Zone) of Andrews (1978) and with those of AMSMZ VI (Coscinodiscus plicatus Partial Range Zone) of Abbott (1978). The Ridgeland diatoms were, therefore, found to be distinctly younger than those of Thomas County, Georgia, studied for this report. The Ridgeland Trough deposit was correlated with ap- proximately the upper half of MLU 16 of the Choptank Formation in the Chesapeake Bay region, whereas the Thomas County deposit of this study has been corre- lated approximately with the lower part of MLU 14. The marine diatoms clearly suggest that the Coosa- whatchie equivalent beds in Thomas County are dis- cernably older than the Coosawhatchie deposit in the Ridgeland Trough. Therefore, the Coosawhatchie de- posits, as a whole, appear to be equivalent to MLU 14 through MLU 16 of the Calvert and Choptank For- mations in Maryland. NONMARINE DIATOM ASSEMBLAGE The nonmarine diatom assemblage in the Coosa- whatchie equivalent beds is the first such Miocene as- semblage to be reported from the southeastern United States. Comparison can be made only with nonmarine assemblages of the Great Plains region, which are both geographically and ecologically far removed from those of southwestern Georgia. The more abundant brack- ish-water component of this assemblage has not been recorded elsewhere in the Miocene and cannot be used in correlation. The three taxa of Eunotia Ehrenberg, 1837, a genus more common to acidic waters, were not observed in the alkaline lake waters of the Great Plains. The remaining six more cosmopolitan fresh- water species in the Coosawhatchie have been ob- served in Miocene deposits of Nebraska. Of these, Gomphonema affine var. insigne (Gregory, 1856) An- drews, 1970 and Pinnularia brevicostata Cleve, 1891, were observed in both the lower Miocene Monroe Creek Sandstone in the Pine Ridge area, Nebraska (Andrews, 1971), and the lower to middle Miocene ‘‘Valentine Formation” at Kilgore, Nebraska (Andrews, 1970). Pinnularia fusana Andrews, 1971, and P. microstau- ron (Ehrenberg, 1843) Cleve, 1891 were observed only in the Monroe Creek Sandstone, and Navicula radiosa Kiitzing, 1844, and Pinnularia torta (Mann, 1924) Pat- rick in Patrick and Reimer, 1966 were observed only in the “Valentine Formation”. Six diatom taxa constitute too small a data base to attempt any precise correlation between the Coosa- 64 BULLETIN 321 whatchie and the Miocene strata of the Great Plains. The Monroe Creek Sandstone is probably of early Mio- cene age, but the “Valentine Formation” would now be considered late early to early middle Miocene in age, rather than uppermost Miocene as stated by An- drews (1970). The small freshwater component of the nonmarine assemblage, although not highly definitive, in no way disagrees with the early middle Miocene age for the Coosawhatchie equivalent beds based on the marine diatom content; it does tend to confirm the observation (Andrews, 1970, 1971) that freshwater diatom assemblages of Miocene age are relatively less diverse than are similar assemblages in Pleistocene and Holocene deposits. AGE OF DIATOM ASSEMBLAGES Although we are in complete agreement in assigning an early middle Miocene age to the Coosawhatchie equivalent of Thomas County, Georgia, and in its rel- ative position in our respective diatom-zonation schemes, we hold slightly divergent opinions in the detailed age assignment of this part of the Miocene section. The following discussion is based on the time- scale of Berggren and Van Couvering (1974). Abbott (1978, p. 26) stated that his AMSMZ IV was correlative with planktonic foraminiferal zone N9 or N10 of Blow (1969), but he preferred to assign his zone to N10. He placed his Zone IV in the lower part of the Serravallian Stage, with an absolute age of just less than 13 Ma (million years). Utilizing more recent correlation in- formation, Abbott (unpub. data) still equates his Zone IV with planktonic foraminiferal zone N10, but he now places this zone in the upper part of the Langhian Stage. Andrews does not find the evidence to assign his ECDZ 4 to Blow’s planktonic foraminiferal zone N10 to be compelling. He therefore prefers to correlate this dia- tom zone with Blow’s zone N9. This would place the Thomas County deposit of the Coosawhatchie equiv- alent beds in the upper part of the Langhian Stage, with an approximate absolute age of 13.4 Ma (Andrews, 1978, p. 379). We regard this only as an interpreta- tional difference of opinion; it does not affect the age assignment of these strata in any significant manner. PALEOECOLOGY The sediments of the Coosawhatchie equivalent beds in Thomas County, Georgia may be logically divided into three parts for discussion of their paleoecology: (1) the lower marine section, exclusive of the upper- most level studied; (2) the uppermost level of the lower marine section and the upper marine bed; (3) the non- marine bed. The relative stratigraphic position of these three paleoecologic elements is shown in Text-fig- ure 4. The lower marine section, exclusive of the upper part, shows a distinctly shallow-water marine diatom assemblage. At the time of deposition there must have been free access to open marine waters even if, as the paleogeography suggests, the strata were deposited in the far end of a narrow embayment extending south- westward from the Atlantic Ocean. The lower marine section, including the fuller’s earth and approx. 5.2 m (17 ft) of overlying clastic sediments, shows an assem- blage dominated by cosmopolitan marine diatoms, many common and widespread in modern marine en- vironments. The most common forms are Paralia sul- cata (Ehrenberg, 1838) Cleve, 1873 and P. s. var. co- ronata (Ehrenberg, 1845c) Andrews, 1976, and Melosira westii Smith, 1856. Many of the marker species are shallow-water benthic taxa, useful in cor- relation with strata as far away as Maryland and New Jersey. Although from the standpoints of location and diatom assemblage, these beds show evidence of shal- low-water deposition, no evidence indicates any sub- stantial deviation from normal marine salinity. The second paleoecologic grouping presents a greater problem. This grouping includes the uppermost part of the lower marine section and the upper marine bed. These two diatomaceous horizons bracket the non- marine bed. These two levels contain similar assem- blages; the one near the top of the lower marine section includes a richer variety of marine species than does the upper marine bed. Both levels are dominated by Actinoptychus aequalis n. sp., which is of little help to us in ecological determination because A. aequalis has not been previously reported. Other more frequently occurring taxa in these beds are: Biddulphia tuomeyi (Bailey, 1844) Roper, 1859, Hyalodiscus scoticus (Kützing, 1844) Grunow, 1879, Paralia sulcata, and P. sulcata var. coronata. Paralia Heiberg, 1863, in- dicates little more than a marine environment. Bid- dulphia tuomeyi and Hyalodiscus scoticus are known to range from shallow-marine to brackish-water en- vironments. Aulacosira italica (Ehrenberg, 1838) Si- monsen, 1979, the only freshwater species identified in the marine deposits, was found rarely in the upper level of the lower marine section. Coupled with the fact that these beds bracket a distinctly brackish-fresh- water diatom assemblage in the nonmarine bed, the evidence suggests a basically marine environment with somewhat lowered salinity. These beds may represent a transition between open marine and nonmarine en- vironments during a temporary regression in the shal- low Gulf Trough or because of blockage of marine waters from the Atlantic Ocean. The nonmarine diatom assemblage shows two dis- tinct elements, one preferring brackish or saline waters and the other fresh waters. The assemblage is domi- MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 65 nated by Melosira juergensi Agardh, 1824, a distinctly brackish-water species. Other taxa tolerant of brackish water or of some salinity are: Caloneis westii (Smith, 1853) Hendey, 1964, Gyrosigma aff. G. spencerii (Quekett, 1848) Griffith and Henfrey, 1856, Navicula aff. N. radiosa Kiitzing, 1844, Nitzschia hybrida Gru- now in Cleve and Grunow, 1880, N. tryblionella var. victoriae (Grunow, 1862) Grunow in Cleve and Gru- now, 1880, and Stauroneis aff. S. salina Smith, 1853. Although there are more fresh- than brackish-water species in the nonmarine bed, the predominance of Melosira juergensi gives an edge to the brackish forms in the total number of specimens. The freshwater taxa include forms ranging in preference from acidic to al- kaline waters and show no distinctive ecologic trend. The occurrence of Eunotia Ehrenberg, 1837, in the sample, however, suggests at least influx of some acidic fresh water. No distinctly marine species occurs in the nonmarine bed, and even the ubiquitous Paralia sul- cata (Ehrenberg, 1838) Cleve, 1873 is absent. This suggests that the connection with the Atlantic Ocean was essentially closed, although some minor influx of brackish or marine water may have taken place from time to time. The mixed brackish- and freshwater dia- tom assemblage suggests deposition in waters of fluc- tuating salinity in a restricted bay or estuary. Appar- ently, relatively little new salt water was being added to the environment. With regard to the sediments themselves, Weaver and Beck (1977) suggested that during the deposition of the fuller’s earth, the presence of phosphate, clay grains, and Na- and K-feldspar indicates that the de- tritus was derived from the Ocala High to the east or southeast. They further suggested that the absence of these minerals and the presence of abundant K-feld- Spar, mica, kaolinite, and a zircon-rutile-tourmaline heavy-mineral suite in the upper part of the deposit indicates a source area in the southern Appalachian Mountains to the west or northwest. SYSTEMATIC PALEONTOLOGY INTRODUCTION The genera and species of diatoms studied for this report are arranged in alphabetical order to facilitate use by the reader. A systematic arrangement has not been made because this paper is of interest primarily to the diatom biostratigrapher, to whom a suprageneric classification is of little consequence. The marine and nonmarine diatom assemblages are treated separately in the text, tables and plates, so that each group can be more readily examined and evaluated. The generic and infrageneric nomenclature generally follows that proposed by Hustedt (1927-1959) and Hendey (1964), but subsequent changes have been taken into account. Descriptions pertinent to the specimens of taxa ob- served in the Hawthorn Formation are included to increase the usefulness of this paper to the reader. More extensive descriptions can usually be found in the works cited in the synonymies. There is no recognized standard for magnification in diatom illustrations, nor is it desirable that one should be imposed. Diatoms vary in maximum dimension from a few to several hundred micrometers. Requiring a constant magnification for all taxa in an ordinary diatom assemblage would result in absurdly small il- lustrations of the smallest diatoms, and illustrations of the largest diatoms could exceed the size of the plate. The selection of diatom magnification is pragmatic with the aim of producing a useful illustration. The light photomicrographs in this report are made at x 500 or X 1000; the electron microscope photographs vary as indicated, depending on the size of the specimen. The measurement of fine structures of diatom valves in number per 10 micrometers, long standard in dia- tom literature, is used throughout this report. The format of discussion follows that used in earlier reports on fossil marine diatom assemblages of the southeastern United States. The first citation in each synonymy is to the basionym of the taxon. The second citation is to the name adopted for use in this report, with appropriate references in chronological order. Subsequent citations include synonyms, misidentifi- cations, misspellings and incorrect attributions of au- thorship. These synonymies emphasize the reported fossil occurrences in the southeastern United States, and they are not intended to be exhaustive. Informa- tion is given in this paper on the known geologic range of all taxa because such information is useful in bio- stratigraphy. The terminology of relative abundance of the various taxa in the studied samples is given in the explanations of Tables 1 and 2. The terms “raised sector” and ““depressed sector" used in describing taxa of the genus Actinoptychus shall by definition refer in this report to the external expression of those sectors. PHILOSOPHICAL CONSIDERATIONS Scientific study of diatoms was initiated for North America by Jacob Whitman Bailey, who published his first paper on diatoms in 1838 and continued active in the field until his death in 1857. Much of Bailey’s work was done on fossil diatoms, both marine and nonmarine, from widely scattered localities in the United States. The first studies of the Tertiary marine diatoms of the Atlantic coastal plain were made by Bailey, and he recognized early that diatoms were as 66 BULLETIN 321 useful for geologic correlation, i.e., biostratigraphy, as were other groups of micro- and macrofossils (Bailey, 1845, p. 337). Bailey was a colleague and correspon- dent of Christian Gottfried Ehrenberg of Berlin, per- haps the best known European diatomist of the 19th century and certainly the most prolific writer of papers on diatoms, both fossil and recent. Many of Ehren- berg’s works on fossil diatoms of North America were based on samples sent to him by Bailey for analysis. Both of these pioneer diatomists seem to have been men of considerable ability. Ehrenberg’s work is better known and much more extensive; he was a recipient of handsome patronage by the kings of Prussia. Bailey, on the other hand, did such diatom work as he could incidental to his duties as a professor at the U. S. Military Academy at West Point, New York. From these beginnings studies of fossil diatoms moved very slowly through the latter part of the 19th century and the early decades of the 20th century. These studies have increased considerably in recent years, so much that it is impossible to summarize the later fossil diatom work here. Fossil marine diatoms as old as Cretaceous were first reported from the Moreno Shale of California by Hanna (1927) and Long, Fuge, and Smith (1946). Well-authenticated diatoms of Creta- ceous age have been reported more recently from the Soviet Union and deep-sea deposits in the ocean ba- sins. Although reports have been made in the literature of fossil diatoms in rocks as old as pre-Cambrian in age, such claims have been generally received with deserved skepticism. The oldest known nonmarine diatom assemblage is that described by Lohman and Andrews (1968) from the late Eocene Wagon Bed For- mation of Wyoming. The earliest diatom assemblages of both marine and nonmarine character are diverse in their component taxa, and this suggests that the diatoms have a much longer history than their record- ed fossil occurrence indicates. Why then do we not find fossil diatoms in rocks older, and even substantially older, than Cretaceous in age? A major consideration appears to be preservation. Older rocks have simply been exposed for longer periods of time to highly varied kinds of percolating waters. The chance of survival of identifiable siliceous remains of diatoms is thus nat- urally decreased with the age of the rocks. Even though Cretaceous rocks are widespread and exposed in thick sections around the world, diatoms are exceedingly rare in Cretaceous deposits. Also, although the evi- dence is not clear from known early diatoms, it is possible that diatoms were not as robustly silicified early in their history as they are at present. We know that many species of diatoms living today are so very weakly silicified that they will not survive more than the mildest cleaning in preparation for study. Such assemblages as the one studied for this report have apparently had all weakly silicified and many moder- ately silicified diatoms destroyed by natural leaching, and they are poor in the more delicate planktonic forms that should be present. We can postulate that diatoms probably developed the ability to form siliceous tests from dissolved silica at some point in their history. At that time they became recognizable as diatoms and as distinct from similar and obviously related soft-bodied microorganisms. This assimilation of silica must have proceeded slowly at first. Because of weak silicification and extremely long times of weathering, it seems doubtful that the oldest diatoms will ever be discov- ered. No classification of diatoms above the generic level has been presented in this paper. This is partly because of the alphabetic, rather than systematic, order of the genera and also because although such classification is of scientific interest, it has little practical use to the diatom biostratigrapher. Diatoms have been classified traditionally as single-celled organisms or cryptogams within the plant kingdom. They are indeed photosyn- thetic organisms, considered by most taxonomists as a definitive characteristic of plants. The Kingdom Pro- tista was proposed by Haeckel (1866) for single-celled organisms with both plant and animal affinities, and more recently the paleontologist R. C. Moore (1954) suggested revival of this classification for the Treatise on Invertebrate Paleontology. The use of a third king- dom does not seem to have received much acceptance from biologists, and biostratigraphers seem almost completely indifferent to the question. Because we know nothing about the earliest evolution of the diatoms, this controversy can probably be solved only on a phil- osophical basis. Perhaps it is simpler to continue to consider the diatoms as plants, but we have no strong convictions on this subject. The classification of diatoms at the family and lesser ranks has been reasonably well stabilized for many years. Generally accepted classifications are published in standard reference works by Hendey (1964) and Hustedt (1927-1959). These works do not always agree in detail, but they present the state of the art as de- veloped under light microscopy. With the advent of electron microscopy a whole new world was revealed in the ultrastructure of diatoms. Transmission electron microscopy gave much greater magnification and res- olution of pore structures. However, scanning electron microscopy has proved even more valuable in mod- elling the surface of the diatom valve with great res- olution, higher magnification, and increased depth of field. The scanning electron microscope now allows the diatomist to see finer structures that were only vaguely discerned as light artifacts, or even not seen at all, under the light microscope. Scanning electron micros- copy has greatly advanced our knowledge of the mor- MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 67 phology of the diatom valve. Consequently, previous diatom classifications have been found to be somewhat inadequate in the light of this new knowledge. A re- vised classification has been made recently by Simon- sen (1979), and further changes will doubtless be made as more information becomes available. Although the electron microscope is extremely useful in diatom re- search, it should by no means be considered as a re- placement for the light microscope. We can increase our knowledge of detailed morphology of the diatom valve by techniques of electron microscopy in order to understand better what we see under the light mi- croscope. No one should be excluded from the study of diatoms because he lacks access to one of these expensive and highly technical instruments. . Diatom research has suffered over the years from a patchwork system of classification (on the generic and subgeneric levels) inherited from a diverse group of 19th century workers. The early workers tended to be conservative and hence “lumpers” in that they did not have adequate microscopes to make significant dis- tinctions nor did they have the experience to recognize significant distinctive features. There are no lack of generic names in the diatom literature, but too many of them were ill-conceived or synonyms for previously described genera. Some past workers were so conser- vative that they retained old classifications long after worthwhile revisions had been made. It seems to me that even today we have too few meaningful diatom genera. As new and distinct genera and species are recognized, even in previously described diatoms, they should be given proper taxonomic revision rather than continued “lumping” into inappropriate categories. Unfortunately, too little taxonomic revision is being done on diatoms at the present time. On the other hand, there seems to have been an excessive amount of “splitting” at the infraspecific level by some work- ers. Species of diatoms are often subdivided into “va- rieties” and these varieties are sometimes even further subdivided into “formas”; subspecies are seldom found in diatom literature. We believe that these infraspecific units may have meaning and utility to the biologist working on living diatoms. However, we do not find them to be useful to the paleontologist, for they imply relationships that are impossible to prove in fossil dia- toms. Although in many instances we have retained the previously described varietal usage in diatom taxa, this is strictly because these varieties seem to show distinct morphology. If a fossil diatom taxon is dis- tinctive enough to be recognized, it deserves the status of a species. Although the classification of fossil dia- toms must be based on valve morphology, biologists continue to find examples of different morphologic for- mas, varieties and even species growing in the same clone of diatoms. It is important that that intraspecific variation be recognized and that diatom taxonomy be modified accordingly. This is a job that the biologist can do much more effectively than the paleontologist. Although diatom taxonomy has probably been more influenced by “lumping” than by “splitting”, occa- sionally the “splitting” seems to have been excessive. Some of the work of Astrid Cleve-Euler comes to mind in this regard, wherein it seems that nearly every spec- imen observed has been given an infraspecific name or letter designation. When we recognize that diatom species show a degree of variability, such fine “split- ting” as this seems to be inappropriate. I have stated my reservations about the validity of quantitative studies on fossil diatoms in an earlier pa- per (Andrews, 1972). Quantification of diatom data has been in vogue in recent years, and some exponents of these techniques are enthusiastic about their results. Quantitative studies may have their value in biological specimens with excellent preservation, but the re- searcher must carefully consider the quality of the sam- ple and the validity of the results produced. They may have value in certain carefully selected situations in paleontological studies, where taxa of relatively equal silicification are being compared. With regard to the samples studied for this report, and from similar shal- low marine deposits of the southeastern United States, quantitative studies seem to be extremely inappro- priate. We know that preservation is only fair in these samples from Thomas County, Georgia, and we have no way of knowing the kinds or quantities of diatoms that have been lost by selective leaching. Furthermore, in the majority of sandy and argillaceous coastal plain deposits there is always an abundance of broken and fragmental specimens, produced either by predeposi- tional breakage in turbulent waters or by compaction between sand grains during lithification. These things preclude any validity to quantitative studies, not only in this region but also in many other fossil diatom deposits. Research on diatoms at the present time is frag- mented into several special interest groups, which are at times diverse in their techniques and purposes. There is a primary dichotomy between diatomists working in biology and in paleontology and another division between workers in marine and in nonmarine diatoms. Much recent work has been done by nonmarine bi- ologists with interests in detecting polluted and en- riched waters. An increasing interest has recently de- veloped in the field of marine diatom biostratigraphy. There is, of course, excellent research also being carried out on the biology of marine diatoms as well as the biostratigraphy of nonmarine diatoms. Unfortunately, communication between these groups is not always as effective as it should be. We paleontologists particu- larly need more precise data on the ecology of living 68 BULLETIN 321 diatoms to interpret properly the paleoecology of our fossil diatoms. It is no longer adequate to know that a diatom taxon is, for example, “of common and wide- spread occurrence in shallow marine coastal waters of eastern North America.” Additional information is ur- gently needed on precise geographic distribution and ecological preference of diatom taxa. Diatom biostra- tigraphers tend to avoid taxonomic problems, because taxonomy is not of pressing importance to meet their immediate needs. Basic considerations for useful dia- tom taxa for biostratigraphers are as follows: (1) the valves of the diatom taxon must be sufficiently silic- ified to be widely preserved as fossils; (2) the diatom taxon must be so morphologically distinct as to be readily recognizable; (3) the diatom taxon must have a restricted stratigraphic range that can be determined; (4) the diatom taxon should have a reasonably wide- spread geographic distribution, that is, it should not be a local endemic species. For routine biostratigraphic work most diatoms can be considered as distinctive objects and correct taxonomy is seemingly not an im- portant consideration. But how can diatomists com- municate with each other without a sound basis of taxonomic understanding? Effective taxonomic studies need to be made by both diatom biologists and pale- ontologists to a greater degree than is seen at present. Greater interchange ofideas between both groups would produce a body of knowledge on diatoms that would not only make for a more accurate science but would also increase the value of diatoms in the various fields of applied research. MARINE DIATOMS Genus ACTINOCYCLUS Ehrenberg, 1838 Actinocyclus ingens Rattray Actinocyclus ingens Rattray, 1890, pp. 149-150, pl. 11, fig. 7; Ka- naya, 1959, pp. 97-99, pl. 7, figs. 6-9; pl. 8, figs. 1-4; Andrews, 1976, p. 13, pl. 3, fig. 10; Abbott and Andrews, 1979, pp. 230- 231, pL digas. Description. — Valve round, nearly flat, but sharply bent at the margin. Margin with fine striations, about 18 in 10 wm, succeeded inwardly by a narrow ring of fine pores in a quincuncial pattern, about 16 in 10 um. The main part of the valve is covered with radial rows of areolae, about four to six in 10 wm, more closely spaced near the margin than near the center, the lengths of the rows dividing the valve into sectors. Areolae near the margin show a slight tendency toward a sec- ondary arrangement in curved decussating rows, are arranged radially in the midpart of valve and more or less randomly near the center. Center of valve is an irregular hyaline area. Pseudonodulus often difficult to observe, but consists of a single small cluster of fine but distinct pores near the shoulder of the valve. Discussion.—This taxon is difficult to distinguish from Coscinodiscus elegans Greville, 1866, a similar appearing diatom without a discernible pseudonodu- lus. The relationship between several species of Actin- ocyclus and analogous morphological forms classified as Coscinodiscus Ehrenberg, 1838, because they show no pseudonodulus, is poorly understood at present. A. ingens was observed by Abbott as rare in sample FE 104 at approximately the 13.1 m (43 ft) level of the lower marine section. Known geologic range.—Reported by Andrews (1976) from the Choptank Formation of Maryland and by Abbott and Andrews (1979) from the Coosawhat- chie Clay Member of the Hawthorn Formation (middle Miocene). Restricted to the Miocene (Barron, 1980). Actinocyclus octonarius Ehrenberg Plate 6, figure 1 Actinocyclus octonarius Ehrenberg, 1838, p. 172, pl. 21, fig. 7; Hen- dey, 1937, p. 262; Lohman, 1941, p. 77, pl. 16, fig. 4; Lohman, 1948, p. 167, pl. 8, fig. 8; Andrews, 1976, p. 14, pl. 3, fig. 7; Abbott and Andrews, 1979, p. 231, pl. 1, fig. 4; Andrews, 1980, p. 23, pl. 1, fig. 1; pl. 4, fig. 1. Actinocyclus ehrenbergii Ralfs in Pritchard, 1861, p. 834; Hustedt, 1929, pp. 525-533, fig. 298. Description. — Valve round, flat, thin and fragile, often fragmented or with damaged margin. Marginal zone covered with rows of fine areolae arranged in a quin- cuncial pattern, about 16 to 20 in 10 um. Main part of valve divided into sectors by single radial rows of areolae extending from the marginal zone to the center. Each sector is filled with parallel rows of areolae, aligned normal to the margin of the valve but not parallel to the dividing rows of areolae. Each sector is thus filled by progressively shorter rows of areolae on both sides of the sector. About 10 rows of areolae in 10 um; about seven areolae in 10 um along the row. Pseudonodulus small, on the inner edge of the marginal zone. Discussion. —Generally rare in the lower marine sec- tion. Known geologic range.— Reported by Hajós (1976) from upper Eocene deposits in the southwestern Pacific and by Fenner (1977) from lower Oligocene deposits in the southern Atlantic. Common in Miocene deposits of the southeastern United States and widespread in modern oceans. Actinocyclus tenellus (Brébisson) Andrews Plate 6, figures 2, 3 Eupodiscus tenellus Brébisson, 1854, p. 257, pl. 1, fig. 9. Actinocyclus tenellus (Brébisson) Andrews, 1976, p. 14, pl. 3, figs. 8, 9; Abbott and Andrews, 1979, p. 231, pl. 1, fig. 9; Andrews, 1980, p. 23. Actinocyclus ehrenbergii var. tenella (Brébisson). Hustedt, 1929, p. 530, fig. 302. MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 69 Description.— Valve small, round, nearly flat, but sharply bent at the margin. Margin with radial rows of very fine areolae, about 18 in 10 um, followed in- wardly by a narrow ring of fine areolae in a quincuncial pattern, about 16 in 10 um. The main part of the valve is divided into about four to six sectors, and the sectors are filled with parallel rows of areolae normal to the margin of the valve as in A. octonarius Ehrenberg, 1838. About 10 rows of areolae in 10 um; about 10 areolae in 10 um along the row. Pseudonodulus at inner margin of quincuncial areolate zone. Discussion. — This species has close affinities for A. octonarius but can be distinguished from that species by its somewhat more robust markings as well as its generally smaller size and fewer sectors. It is more frequently observed in this deposit than A. octonarius. Rare to frequent in the lower marine section and rare in the upper marine bed. Known geologic range.—Miocene to Holocene, widespread in modern oceans. Genus ACTINOPTYCHUS Ehrenberg, 1841 Actinoptychus aequalis Andrews, new species Plate 6, figures 4-7, 10-13; Plate 10, figures 17, 18; Plate 11, figures 1-6 Description.—Valve round with narrow slanting Marginal rim surrounding a main area of raised and depressed sectors. Diameter of observed specimens 37- 91 um. Outer slanting rim (Pl. 11, fig. 1) ornamented with radial rows of fine pores, about 30 in 10 wm and also with external radial ridges of silica. At the shoulder of each externally raised sector with the rim is a single pore, centered, with a thickened rim or extended out- ward as a short tube (PI. 11, fig. 3). These external pores or tubes connect with single labiate processes on the inside of the valve. The labiate processes, when preserved, are relatively long and curved (PI. 11, fig. 4). Main part of valve sharply divided into raised and depressed sectors, eight to 18 specimens observed. These sectors may be very nearly equal in width, but in some specimens alternate sectors are distinctly wider or narrower. There is no consistency as to which set of sectors is the widest. The raised sectors show a coarse areolate net on the outside of some specimens, which is much reduced or almost vestigial in others (see dis- cussion below). Even when well-developed, the pattern of the areolate net is irregular. The depressed sectors show only vestiges of an areolate net, or more com- monly, none at all. The predominant ornamentation of the main part of the valve is the pore pattern, which can be observed well on both the inside and outside of the valve. The pores are arranged in a hexagonal net over both raised and depressed sectors, about 18 to 20 pores in 10 um along the row, slightly more closely spaced in the de- pressed sectors. On the inside of the valve is a distinctly raised rim around each pore. Central area hyaline, warped at margins to attach to undulating sectors. It is subpolygonal in outline and does not extend into the sectored part of the valve. Discussion.—The specific name aequalis is given to this taxon because of the evenness of the pore pattern (both spacing and design) over both the raised and depressed sectors. All six-sectored specimens observed in this study have been assigned to A. senarius (Eh- renberg, 1838) Ehrenberg, 1843, although some of them show an evenness of pore pattern that approaches A. aequalis. What is considered to be A. senarius in this deposit frequently shows a variable placement in the labiate processes (see discussion of A. senarius), where- as A. aequalis as herein defined shows only the basic single labiate process centered on the shoulder of each raised sector. A. aequalis probably has evolved from A. senarius, but it is impossible to determine in a fossil assemblage whether or not these two morphologic species formed an interbreeding population. A. aequalis was rare in the 18.3, 17.4, and 16.5 m (60, 57, and 54 ft) levels of the lower marine section, frequent in the 12.8 m (42 ft) and common in the 8.8 m (29 ft) (or uppermost) level. It was also common in the upper marine bed at the 4.6 m (15 ft) level. Spec- imens from the lower part of the lower marine section observed under the scanning electron microscope showed a more strongly developed external areolate net than did those from the top of the lower marine section. Whether this is an example of microevolution or a response to some undefined ecological factor is uncertain. Known geologic range.—Not previously reported. Whether A. aequalis had a widespread distribution during the middle Miocene or whether it was restricted ecologically or geographically, perhaps even to this sed- imentary basin, is not known. The species is most com- mon in the assemblages that suggest deviation from normal marine ecological conditions. Holotype. — USNM No. 372375 and USGS Diatom Catalog No. 3971-1 (Pl. 6, figs. 6, 7), diameter 57 um. From USGS diatom locality 6469, the 8.8 m (29 ft) level (and uppermost studied sample) of the lower ma- rine section, Oil-Dri fuller’s earth pit, about 2 mi northwest of Ochlocknee, Thomas County, Georgia. The holotype is accessioned into the paleobotany col- lection located in the U. S. National Museum of Nat- ural History, Washington, DC, 20560. The holotype is deposited in the USGS diatom col- lection located in the U. S. National Museum of Nat- ural History, Washington, DC. At such time as this collection ceases to be a working collection of the 70 BULLETIN 321 U. S. Geological Survey, it will by law be formally accessioned to the U. S. National Museum. Actinoptychus marylandicus Andrews Plate 6, figures 8, 9 Actinoptychus marylandicus Andrews, 1976, p. 14, pl. 4, figs. 3-6; Andrews, 1978, p. 383, pl. 2, figs. 1, 2; Abbott and Andrews, 1979, p232, ple T; Tig: TO? Description. — Valve round, discoid, fragile, with margin often missing or poorly preserved. Main part of valve divided into sectors, usually about 14 to 18, alternately elevated and depressed, each group with distinctive fine markings. Group 1 (externally de- pressed, coarsely areolate sectors): single row of areolae at margin, succeeded inwardly by a narrow but distinct hyaline band; main part of sector covered with parallel rows of areolae, about 10 in 10 um, normal to the margin and arranged in a quincuncial pattern; a blade- like hyaline area in the center of the sector extends from the hyaline central area about one-third to one- half the length of the sector; this bladelike hyaline area results from the absence of one to three rows of areolae in the center ofthe sector. Group 2 (externally elevated, finely punctate sectors): each sector has single labiate process centrally situated near the margin; main part of the sector covered with fine areolae, about 16 in 10 um, arranged in a hexagonal pattern. Many specimens show a shorter, narrower hyaline blade analogous to the larger blades in alternate sectors. Central area hya- line, vaguely marked, warped near the margin to join alternate sectors on different planes. Discussion. — This important marker species is sim- ilar in morphology to A. virginicus (Grunow in Van Heurck, 1883) Andrews, 1976, except that the hyaline areas in the depressed sectors are bladelike rather than irregular. Rare in the 14.6 m (48 ft) level of the lower marine section. Known geologic range. — Middle Miocene, reported by Andrews (1978) from unit 12 of the Calvert For- mation through unit 20 of the Choptank Formation in Maryland. Reported by Abbott and Andrews (1979) from the Coosawhatchie Clay Member of the Haw- thorn Formation. Actinoptychus senarius (Ehrenberg) Ehrenberg Plate 6, figures 14, 15; Plate 12, figures 1, 2 Actinocyclus senarius Ehrenberg, 1838, p. 172, pl. 21, fig. 6. Actinoptychus senarius (Ehrenberg) Ehrenberg, 1843, p. 400, pl. 1, fig. 27; Hendey, 1937, pp. 271-272; Lohman, 1941, pp. 80-81, pl. 16, fig. 9; Hendey, 1964, p. 95, pl. 23, figs. 1, 2; Andrews, 1976, p. 15, pl. 4, figs. 7, 8; Abbott and Andrews, 1979, p. 232, pl. 1, fig. 11; Andrews, 1980, p. 24, pl. 1, fig. 3. Actinoptychus undulatus (Bailey) Ralfs. Hustedt, 1929, pp. 475-478, fig. 264. Description. — Valve round, discoid, divided into 6 sectors, alternately elevated and depressed, each group showing different markings. Group 1 (externally de- pressed, coarsely areolate sectors): surface completely and regularly covered with a hexagonal network of fine areolae, about 17 in 10 um. This layer is overlain by an indistinct net of larger hexagonal areolae, about four in 10 um; each sector has a minimum of one labiate process on the margin of the valve at the center of the sector, and there may be others on the valve as indi- cated in the discussion below. Central area hyaline, vaguely marked, warped near margin to join alternate sectors on different planes. Discussion. — Frequent throughout the lower marine section and rare in the upper marine bed. This species is the basic six-sectored form of Actinoptychus, which could perhaps be divided after further study. The long- ranging basic form shows a single internal labiate pro- cess centered on the margin of each externally raised sector. Specimens observed under the scanning elec- tron microscope in this deposit show the following forms: (1) the basic form, having a single central labiate process on each raised sector; (2) a variety having an addition, inconsistently, ofa single labiate process near the edge of the raised sectors; (3) a variety in which each raised sector shows three labiate processes, one central, one near each edge; (4) a variety that has, in addition to processes shown by variety three, the ir- regular occurrence of a single labiate process, not cen- tered, in the depressed sectors; (5) the most advanced variety, having three labiate processes on each raised sector, two on each depressed sector, all subevenly distributed around the margin of the valve. These vari- ations in placement of the labiate processes are rem- iniscent of those reported for Actinoptychus heliopelta Grunow in Van Heurck, 1883 by Andrews (1979). These variations are thought to represent only varia- tion in a population and not to be of taxonomic sig- nificance. Known geologic range. — Cretaceous to Recent (com- mon in cool coastal waters of modern oceans). Com- mon in the Neogene deposits of the southeastern United States. Actinoptychus thumii (Schmidt) Hanna Actinoptychus stella var. thumii Schmidt, 1886, pl. 90, figs. 3-5; Pantocsek, 1886, pt. 1, pp. 65-66, pl. 8, fig. 65. Actinoptychus thumii (Schmidt) Hanna, 1932, p. 171, pl. 4, figs. 3, 4; Andrews, 1978, pp. 383-384, pl. 3, figs. 8, 9. Description. — Valve round, discoid, divided into six alternately elevated and depressed sectors. The crimp- ing of the valve is relatively sharp and deep. The whole valve has a stellate pattern of ornamentation, often not readily observed because of the disparity of focus in MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT El alternate sectors. Outer margin of valve has a narrow band of very fine areolate structure. Group 1 sectors (externally depressed): more coarsely marked than al- ternate sectors, with a triangular area covered with areolae arranged in a hexagonal pattern, about 22 in 10 um, completely surrounded by a hyaline band about 2 um wide. Group 2 sectors (externally elevated): cov- ered with very fine areolae; a single prominent labiate process occurs in the center of its punctate rim seg- ment; a narrow hyaline ray extends from area of labiate process to central area. Central area hyaline, about one- sixth width of valve. Discussion. — Rare in the upper marine bed. Known geologic range.—Reported by Andrews (1978) from lithologic unit 14 of the Calvert Formation in Maryland. Early middle Miocene age. Actinoptychus virginicus (Grunow) Andrews Actinoptychus vulgaris var. virginica Grunow in Van Heurck, 1883, pl. 121, fig. 7. Actinoptychus virginicus (Grunow) Andrews, 1976, p. 15, pl. 4, figs. 9-12; Andrews, 1978, p. 384, pl. 2, figs. 2-5; Abbott and Andrews, 1979, pp. 232-233, pl. 1, fig. 12. Description.—Valve round, discoid, fragile, with margin often missing or poorly preserved. Main part of valve divided into sectors, usually about 10 to 18, alternately elevated and depressed, each group showing different fine markings. Group 1 (externally depressed, coarsely areolate sectors): single row of areolae at mar- gin, succeeded inwardly by a narrow but distinct hya- line band; main part of sector covered with parallel rows of areolae, about 10 in 10 um, normal to the margin and arranged in a quincuncial pattern; an ir- regular hyaline area occurs in the center of each sector, seemingly an extension of the hyaline central area of the valve. Group 2 (externally elevated, finely areolate sectors): main part of sector covered with fine pores, about 16 in 10 um, arranged in a hexagonal pattern; small bladelike hyaline extensions usually not present, or much less noticeable than in A. marylandicus An- drews, 1976; a single labiate process is centrally situ- ated near the margin. Central area hyaline, vaguely marked, warped near the margin to join alternate sec- tors on different planes. Discussion. — Although A. virginicus is usually more frequent than the related species A. marylandicus in Miocene deposits of the southeastern United States, here only a rare occurrence was found by Abbott in sample FE 104 at approximately the 13.1 m (43 ft) level of the lower marine section. Known geologic range.—Middle Miocene, from the lower part of lithologic unit 13 of the Calvert For- mation to at least the top of the Choptank Formation in Maryland (Andrews, 1978). Genus AMPHIPRORA Ehrenberg, 1843 Amphiprora aff. A. alata (Ehrenberg) Kiitzing Plate 6, figure 16 Navicula alata Ehrenberg, 1840, p. 212. Amphiprora alata (Ehrenberg) Kiitzing, 1844, p. 107, pl. 3, fig. 63; Hustedt, 1930a, p. 340, fig. 625; Hendey, 1964, p. 253, pl. 39, figs. 14-16. Description.— Valves linear, constricted in middle and twisted. Raphe enclosed in axial area raised to form a sigmoid keel. Surface of valve covered with rows of fine areolae with a primary longitudinal and secondary transverse orientation. Keel coarsely punc- tate. Discussion. — Observed as rare in the 18.3 m (60 ft) level of the lower marine section. It appears to be close to A. alata, but absolute identification could not be made. Known geologic range.—Not previously reported as a fossil species. Common in modern coastal waters having lowered salinity. Genus ANAULUS Ehrenberg, 1844 Anaulus birostratus (Grunow) Grunow Biddulphia birostrata Grunow, 1863, p. 158, pl. 13, fig. 23. Anaulus birostratus (Grunow) Grunow in Van Heurck, 1882, pl. 103, figs. 1-3; Hustedt, 1930, p. 893, fig. 536; Abbott and Andrews, 1979, 9.233. pl. lige 13. Description. — Valve fusiform, elongate, with slightly concave lateral margins. Ends subrostrate, attenuate, with bluntly rounded apices. Two transverse septa di- vide the valve into three chambers of subequal length, and maximum widths of valve are near crossing points of these septa. Valve surface covered with randomly distributed pores. A single internal labiate process is slightly off center in the central chamber. Discussion. —Observed as rare by Abbott in sample FE 104 at approximately the 13.1 m (43 ft) level of the lower marine section. Known geologic range.—Reported by Abbott and Andrews (1979) from the middle Miocene Coosa- whatchie Clay Member of the Hawthorn Formation. This benthonic species is common in coastal environ- ments of the warmer modern oceans. Genus AULACODISCUS Ehrenberg, 1844 Aulacodiscus argus (Ehrenberg) Schmidt Plate 7, figure 1 Tripodiscus argus Ehrenberg, 1841, p. 159, pl. 3, fig. 6. Aulacodiscus argus (Ehrenberg) Schmidt, 1886, pl. 107, fig. 4; Rat- tray, 1888a, p. 373; Hustedt, 1929, pp. 503-505, fig. 281; Lohman, 1948, p. 171; Hendey, 1964, p. 97; Andrews, 1980, pp. 24-25. Description.— Valves round, surface flat to slightly convex, completely covered with a coarse network of 29 BULLETIN 321 angular areolae that overlies a lower lamina with much finer pores. The valve appears to be heavy and dense and the areolation pattern is distinctive. Two to six processes are subequally spaced near the margin of the valve. Their external expression is as a siliceous tube, which is presumably connected to a labiate process on the inside of the valve. Discussion. — Usually occurring as distinctive frag- ments; rare to frequent in the lower marine section and frequent in the upper marine bed. Known geologic range. — Miocene to Holocene. A widespread neritic occurrence around the North At- lantic Ocean. Genus AULACOSIRA Thwaites, 1848 Aulacosira italica (Ehrenberg) Simonsen Plate 6, figure 17 Gaillonella italica Ehrenberg, 1838, p. 171, pl. 10, fig. 6. Aulacosira italica (Ehrenberg) Simonsen, 1979, p. 55. Melosira italica (Ehrenberg) Kiitzing, 1844, p. 55, pl. 2, fig. 6; Hu- stedt, 1927, pp. 257-262, fig. 109; Lohman and Andrews, 1968, p. E12, pl. 1, fig. 6; Andrews, 1970, p. A9, pl. 1, fig. 4; Andrews, 1971, p ES DLL Bes. T; 2: Description. — Valves cylindrical, bound in chains of frustules, usually greater in height than in diameter, so consequently more commonly seen in girdle view. Mantle finely areolate, about 14 areolae in 10 um, arranged in longitudinal or slightly spiral rows, about 16 in 10 um. Denticulate processes on face of valve link adjoining frustules. Discussion.—The only distinctly freshwater taxon observed in these marine deposits. Rare in the 10.4 m (34 ft) level of the lower marine section; the diatom assemblage at this level seems to be affected by lower salinity. A. italica in this assemblage may well have been washed in from a freshwater environment. Known geologic range.— Reported from deposits as old as early Miocene by Andrews (1971). A common and widespread pelagic form in modern freshwater en- vironments. Genus AULISCUS Ehrenberg, 1843 Auliscus sculptus (Smith) Ralfs Plate 7, figures 2, 3 Eupodiscus sculptus Smith, 1853, p. 25, pl. 4, fig. 42. Auliscus sculptus (Smith) Ralfs in Pritchard, 1861, p. 845; Greville, 1863, pp. 43-44, pl. 3, figs. 1-3; Rattray, 1888b, p. 883; Hustedt, 1929, pp. 516-518, fig. 290; Hendey, 1964, pp. 98-99, pl. 23, fig. 4. Auliscus caelatus Bailey, 1854, p. 6, pl. 1, figs. 3, 4; Ralfs in Pritchard, 1861, p. 845; Greville, 1863, pp. 44-45, pl. 2, figs. 4-7; Hustedt, 1929, pp. 518-522, figs. 291-295. Description. — Valves nearly circular to broadly el- liptical. Two large, slightly produced ocelli located near the margin on a line slightly oblique to the longitudinal axis. Surface of valve ornamented with costae or thick- enings radiating from the margin of the valve and from the ocelli to a distinct, rounded, hyaline central area. Discussion. — Observed as rare in the 14.6 and 18.3 m (48 and 60 ft) levels of the lower marine section. Known geologic range. — Not previously reported as a fossil species. Common in modern temperate coastal waters. Genus BIDDULPHIA Gray, 1821 Biddulphia arrita (Lyngbye) Brébisson Plate 7, figure 4 Diatoma auritum Lyngbye, 1819, p. 182, pl. 62, fig. D. Biddulphia aurita (Lyngbye) Brébisson, 1838, p. 12; Hustedt, 1930, pp. 846-849, fig. 501; Hendey, 1964, p. 103, pl. 24, fig. 6; Abbott and Andrews, 1979, p. 233, pl. 2, fig. 1. Description.— Valves elliptical-lanceolate in outline, convex in center and showing a single prominent horn on each end. Entire surface of valve, including horns, covered with large areolae, arranged in rows radiating from the center of the valve. Two or more long spines project from the raised center of the valve. Discussion. — Rare and infrequent in the lower ma- rine section and rare in the upper marine bed. Some- times difficult to distinguish from Triceratium spino- sum Bailey, 1844, in girdle view under the light microscope. Known geologic range. —Reported by Abbott and Andrews (1979) from the Coosawhatchie Clay Mem- ber of the Hawthorn Formation (middle Miocene). Common in modern shallow coastal waters. Biddulphia tuomeyi (Bailey) Roper Plate 7, figures 5-8 Zygoceros tuomeyi Bailey, 1844, p. 138, pl. 3, figs. 3-9. Biddulphia tuomeyi (Bailey) Roper, 1859, p. 8, pl. 1, figs. 1, 2; Gru- now in Van Heurck, 1882, pl. 98, figs. 2, 3; Hustedt, 1930, pp. 834—836, fig. 491; Lohman, 1948, p. 174; Andrews, 1976, p. 17, pl. 5, fig. 11; Abbott and Andrews, 1979, p. 234, pl. 2, fig. 4; pl. 6, fig. 8; Andrews, 1980, pp. 25-26, pl. 1, figs. 10, 11; pl. 4, fig. 5. Description. —Girdle view of valve shows base slightly extended beyond main part of valve, which consists of a large bulbous central process, two to eight smaller domed lateral processes and two elongate, tu- bular apical processes with closed ends. Surface of valve covered sparingly with large areolae, arranged radially on the bulbous central process but with near random distribution elsewhere. Mantle of valve covered with rows of fine areolae normal to the valve margin. The ends of the central process may show several protrud- ing spine-like structures. Discussion. — Rare to frequent in the lower marine section and frequent in the upper marine bed. Many specimens show four or more lateral bulbous processes, MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 73 and a few show remnants ofa finely punctate siliceous membrane, draped marginally between the tubular apical processes. This membrane is rarely observed in fossil specimens. Known geologic range.— Cretaceous to Holocene, according to Lohman (1948). Occurs with varying fre- quency throughout the Neogene deposits of the south- eastern United States. Frequent in modern coastal waters of warmer oceans and ranges into brackish en- vironments. Genus COSCINODISCUS Ehrenberg, 1838 Coscinodiscus asteromphalus Ehrenberg Coscinodiscus asteromphalus Ehrenberg, 1844, p. 77; Hustedt, 1928, pp. 452-454, fig. 250; Hendey, 1964, p. 78, pl. 24, fig. 2; Abbott and Andrews, 1979, p. 235, pl. 2, fig. 8. Description. — Observed only as fragmental material. The large size of the disk, central rosette, coarse areolae and the secondary structures within the areolae are sufficient to identify the species. Discussion. — Observed as rare by Abbott in sample FE 104 at approximately the 13.3 m (43 ft) level of the lower marine section. Known geologic range.—Frequently observed as fragments in Miocene to Holocene deposits of the southeastern United States and elsewhere. This plank- tonic species has a worldwide distribution in modern Oceans. Coscinodiscus curvatulus Grunow Plate 7, figure 9 Coscinodiscus curvatulus Grunow in Schmidt, 1878, pl. 57, fig. 33; Hustedt, 1928, pp. 406-410, fig. 214; Lohman, 1941, p. 74, pl. 15, fig. 8; Lohman, 1948, p. 160; Hendey, 1964, p. 81; Andrews, 1976, p. 10, pl. 2, fig. 4; Abbott and Andrews, 1979, p. 236, pl. 2, fig. 12; Andrews, 1980, p. 27, pl. 4, fig. 4. Description. — Valve round, flat, divided into about 11 to 12 curved sectors. Each sector defined by a curved row of areolae extending from margin to center, the remainder of the sector filled by progressively shorter rows of areolae, decreasing in length toward the margin of the adjacent sector. About five to six areolae in 10 um, arranged in curved radial rows as well as second- arily in a decussating pattern. No distinct central area. Narrow marginal rim finely areolate, about 12 areolae in 10 um. Discussion. — Rare in some samples from the lower marine section. Known geologic range. — Throughout the Neogene deposits of the southeastern United States; a frequent pelagic form in modern oceans. Coscinodiscus decrescens Grunow Coscinodiscus decrescens Grunow in Schmidt, 1878, pl. 61, figs. 8, 9; Rattray, 1889, p. 525; Hustedt, 1928, p. 430, fig. 233; Hendey, 1964, p. 77; Abbott and Andrews, 1979, p. 236, pl. 2, fig. 12. Description.— Valves round, markedly convex, cov- ered with a coarse areolate net. Areolae arranged in a crudely spiral arrangement emanating from the center of the valve. About four areolae in 10 um near the center, decreasing in size to about six in 10 um near the margin. No central area or rosette. A few fine pores are scattered randomly in the areolate net. Discussion. — Observed by Abbott as frequent in sample FE 101, at approximately the 16.7 m (55 ft) level of the lower marine section. Known geologic range. — Reported from the Coosa- whatchie Clay Member of the Hawthorn Formation by Abbott and Andrews (1979); hence, at least as old as middle Miocene to modern cool-water marine en- vironments. Coscinodiscus gigas var. diorama (Schmidt) Grunow Coscinodiscus diorama Schmidt, 1878, pl. 64, fig. 2. Coscinodiscus gigas var. diorama (Schmidt) Grunow, 1884, p. 76; Rattray, 1889, p. 542; Abbott and Andrews, 1979, pp. 236-237, pl. 2, fig. 14. Description. — Valve round, large, slightly convex. Valve ornamented with wavy radial rows of areolae near the center, becoming more closely packed into an areolate net a short distance out, and so extending to the margin. About seven areolae in 10 um near the center, increasing in size to about three-and-one-half in 10 um near the margin. Margin with rows of fine areolae. Areolate net predominantly oriented in radial rows with a much less prominent secondary orienta- tion in wavy decussating rows. Central area hyaline; short hyaline rays extend outward between rows of pores. Discussion.— C. gigas var. diorama was observed as rare by Abbott in samples FE 101, FE 103 and FE 104 at the approximate 18.3, 13.7 and 13.1 m (60, 45 and 43 ft) levels of the lower marine section. Known geologic range. — Reported by Rattray (1889) from the Miocene “Santa Monica" and “Monterey” diatom assemblages of California and by Abbott and Andrews (1979) from the middle Miocene Coosa- whatchie Clay Member of the Hawthorn Formation. Not reported in Holocene marine environments. Coscinodiscus lacustris Grunow Plate 7, figure 10 Coscinodiscus lacustris Grunow in Cleve and Grunow, 1880, p. 114; Hustedt, 1928, pp. 432-433, fig. 235; Abbott and Andrews, 1979, p.237, pb 2. 5g. 17. 74 BULLETIN 321 Description.— Valve round, irregularly warped, markedly convex at margin. Valve covered with irreg- ular radial rows of areolae, about 12 rows in 10 um. Some areolae are elongate in a radial direction. Margin narrow, finely areolate, with irregularly placed small processes along its inner edge. Discussion. — Rare in the 13.7 m (45 ft) level of the lower marine section. Known geologic range.—Reported previously from rocks as old as Miocene by Abbott (1980), and widely observed in nonmarine fossil deposits of the Great Plains area. Apparently tolerates salinity ranging from shallow marine coastal waters and brackish waters into essentially freshwater environments. Coscinodiscus marginatus Ehrenberg Coscinodiscus marginatus Ehrenberg, 1843, p. 329, 371; Ehrenberg, 1854, p. 18, fig. 44; pl. 33, XII, fig. 13; pl. 38, XXII, fig. 8; Hustedt, 1928, pp. 416-418, fig. 223; Hendey, 1964, p. 78, pl. 22, fig. 2; Andrews, 1976, p. 11, pl. 2, figs. 6, 7; Abbott and Andrews, 1979, P- 238, pl-.3, fig. 2. Description. — Valve round, slightly convex. Surface of valve covered with a net of strong and large hex- agonal areolae, about three-and-one-halfin 10 um. Ar- eolae arranged irregularly in roughly radial rows and increasing in size toward the center from the margin. Prominent marginal rim covered with fine radial striae. Areolate net covers the center of the valve. Discussion. — Observed as rare by Abbott in samples FE 102 and FE 104 and as frequent in sample FE 106 at levels of approximately 15.2, 13.1 and 10.7 m (50, 43 and 35 ft) respectively, of the lower marine section; he observed it as rare in sample FE 110 at a level of 4.6 m (15 ft) in the upper marine bed. Known geologic range.— Cretaceous to Holocene, according to Abbott and Andrews (1979). Coscinodiscus oculus-iridis Ehrenberg Coscinodiscus oculus-iridis Ehrenberg, 1841, p. 147; Ehrenberg, 1854, pl. 18, fig. 42; pl. 19, fig. 2; Hustedt, 1928, pp. 454—456, fig. 252; Hendey, 1964, p. 78; Andrews, 1976, p. 11, pl. 2, fig. 8; Abbott and Andrews, 1979, p. 238, pl. 3, fig. 4. Description. — Valve round, large, flat. Marginal rim marked by short striae, about four to five in 10 um. Main part of valve covered by areolae primarily or- dered in radial rows and secondarily ordered in curved decussating rows. Areolae fill the valve surface by in- tercalation of progressively shorter radial rows toward the valve margin. About three areolae in 10 um, but somewhat smaller near the margin. Center of valve shows a rosette of elongate radiating areolae. Discussion. — Observed as rare in the 13.7 m (45 ft) level of the lower marine section. A large and fragile diatom, which may be easily broken and hence not readily identified. Known geologic range.— Throughout the Tertiary into modern marine environments, according to Loh- man (1948). Coscinodiscus perforatus Ehrenberg Plate 7, figures 11-13 Coscinodiscus perforatus Ehrenberg, 1844, p. 78; Ehrenberg, 1854, pl. 18, fig. 46; Hustedt, 1928, pp. 445—449, fig. 245; Lohman, 1948, p. 163; Hendey, 1964, pp. 77-78; Andrews, 1976, p. 11, pl. 2, fig. 9; Abbott and Andrews, 1979, p. 239, pl. 3, fig. 5. Description. — Valve round, flat, surface covered by areolae with a primary orientation in radial rows and a secondary orientation in curved decussating rows. Areolae fill the valve surface by intercalation of pro- gressively shorter rows toward the valve margin, each row terminated centrally by a single small pore. Ar- eolae for the most part distinctly round and not com- monly squeezed into a polygonal shape by close pack- ing. About six areolae in 10 um at half-radius position, slightly finer near center and margin. A small hyaline central area is commonly present. Discussion. — Rare to frequent in most samples from the lower marine section. Two of the specimens in- cluded herein (Pl. 7, figs. 11, 12) are small specimens that are somewhat atypical for the species. They re- semble the form in the Petersburg assemblage (An- drews, 1980, p. 27, pl. 1, fig. 18) described as Cosci- nodiscus nitidus Gregory, 1857. This taxon has since been properly recognized as a pseudocentric diatom with affinities for Rhaphoneis Ehrenberg, 1845, and renamed as Psammodiscus nitidus (Gregory, 1857) Round and Mann, 1980. These Miocene forms are clearly a species of Coscinodiscus Ehrenberg, 1838, and they seem to be most closely allied to C. perforatus. Known geologic range. — Miocene (Calvert Forma- tion of Maryland) to Recent (common in modern ma- rine environments). Coscinodiscus perforatus var. cellulosus Grunow Plate 7, figure 14 Coscinodiscus perforatus var. cellulosa Grunow, 1884, p. 75; Hu- stedt, 1928, p. 447, fig. 246; Lohman, 1948, pp. 163-164, pl. 8, fig. 3; Andrews, 1976, p. 11, pl. 2, fig. 10; Abbott and Andrews, 1979 p. 239, pl. 3, fig. 6. Description. — The variety cellulosus is similar to the typical variety, except that the areolae are polygonal in outline because of tight packing, rather than large discrete round openings. Discussion. — Rare to frequent in the lower marine section. Known geologic range. — Miocene to Holocene ma- rine environments. MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 75 Coscinodiscus rothii (Ehrenberg) Grunow Plate 7, figure 15; Plate 8, figure 1 Heterostephania rothii Ehrenberg, 1854, pl. 35A, XIIIB, figs. 4, 5. Coscinodiscus rothii (Ehrenberg) Grunow, 1878, p. 125; Hustedt, 1928, pp. 400-406, fig. 211; Andrews, 1976, p. 12, pl. 3, figs. 1, 2; Abbott and Andrews, 1979, p. 239, pl. 3, fig. 9. Description. — Valve round, concentrically undulate, raised upward from margin to an annular ring, but depressed in center. Surface of valve divided into many sectors, each defined by a relatively straight row of areolae from the margin to the center, then by pro- gressively shorter rows to the edge of the adjacent sec- tor. Areolae round, about seven in 10 um with a pri- mary orientation in the subradial sectoral pattern and a secondary orientation in curved decussating rows. The center may have a narrow hyaline ring enclosing a few areolae. Discussion. — Rare to frequent throughout the lower marine section. This species has obvious affinities for the genus Actinocyclus Ehrenberg, 1838, and indeed the varieties normani and subsalsa have been reclas- sified as Actinocyclus normanii and A. normanii forma subsalsa by Hustedt (1957a, pp. 218-220) and this classification has been confirmed by Hasle (1977). Both of these taxa show a definite pseudonodulus. With regard to Coscinodiscus rothii sensu stricto, Hustedt (19572, p. 219), although he recognized the close sim- ilarity to Actinocyclus in morphology, examined many specimens of C. rothii and was unable to find the pseu- donodulus necessary for its reclassification as Actino- cyclus. Hence, I am retaining this diatom as a species of Coscinodiscus, recognizing that there are difficulties in separating some species of Coscinodiscus from Ac- tinocyclus under the currently accepted classification. Known geologic range. — From the lower to middle Miocene Calvert Formation of Maryland to Recent (common in modern marine environments). Coscinodiscus stellaris Roper Coscinodiscus stellaris Roper, 1858, p. 21, pl. 3, fig. 3; Hustedt, 1928, pp. 396—398, fig. 207; Lohman, 1941, pp. 68-69, pl. 13, fig. 2; 1948, p. 164; Hendey, 1964, p. 81; Abbott and Andrews, 1979, p. 240, pl. 3, fig. 10. Description. — Valves round, convex, thin. Surface of valve covered with a net of fine areolae in radial and curved decussating rows, warped in certain areas to produce irregularly sized fascicles. Irregularly shaped hyaline central area with about three to six extended arms, forming a roughly starlike pattern. Discussion. — Observed as rare in sample FE 104 at approximately the 13.1 m (43 ft) level of the lower marine section. Known geologic range.— Calvert Formation (lower to middle Miocene) of Maryland (Lohman, 1948); Coosawhatchie Clay Member of the Hawthorn For- mation (middle Miocene) of South Carolina and Geor- gia (Abbott and Andrews, 1979). A common plank- tonic species with worldwide distribution in modern oceans. Coscinodiscus vetustissimus Pantocsek Coscinodiscus vetustissimus Pantocsek, 1886, pt. 1, p. 71, pl. 20, fig. 186; Hustedt, 1928, pp. 412-414, fig. 220; Lohman, 1938, p. 86, pl. 20, fig. 7; Andrews, 1976, p. 12, pl. 3, fig. 3; Abbott and Andrews, 1979, p. 240, pl. 3, fig. 11. Description. — Valve round, flat. Surface covered with areolae, closely packed in a polygonal net; about five areolae in 10 um. Areolate net has a primary radial orientation and a poorly defined secondary orientation in curved decussating rows. Areolate net is fasciculate, dividing the valve into many ill-defined sectors, each limited by a relatively straight row of areolae from margin to center, then by progressively shorter parallel rows to edge of adjacent sector. The center ofthe valve contains a small cluster of areolae surrounded by an irregular hyaline ring. Margin of valve finely striate, about 12 in 10 um. Discussion.—Observed by Abbott as rare in samples FE 101, FE 104, and FE 106 at the approximate 16.8, 13.1 and 10.4 m (55, 43 and 34 ft) levels of the lower marine section. Known geologic range. — Middle Miocene to Plio- cene, according to Abbott and Andrews (1979). Genus CYMATOGONIA Grunow, 1883 Cymatogonia amblyoceros (Ehrenberg) Hanna Plate 8, figures 2, 3 Triceratium amblyoceros Ehrenberg, 1844, p. 88; Ehrenberg, 1854, ‚pl. 18, fig. 51. Cymatogonia amblyoceros (Ehrenberg) Hanna, 1932, p. 186, pl. 10, fig. 5; Lohman, 1948, pp. 170-171, pl. 9, fig. 7; Abbott and An- drews, 1979, p. 241, pl. 3, fig. 16. Actinoptychus amblyoceros (Ehrenberg) Schmidt, 1874, pl. 1, fig. 25. Description. — Valve triangular with broadly round- ed corners. Surface undulatory between six sectors, al- ternate sectors on the same plane. Sectors ornamented with rows of fine areolae, about 13 to 14 in 10 um, arranged in a hexagonal pattern. A labiate process oc- curs at one side of the bisector of each angle and close to the margin. Narrow marginal area depressed and marked by somewhat finer pore structure. Hyaline cen- tral area irregular in size and shape, commonly roughly triangular. Discussion. —Generally rare in the lower marine sec- tion and in the upper marine bed. An excellent marker fossil because it can be identified from any fragment showing the small hyaline central area. 76 BULLETIN 321 Known geologic range.— Although this distinctive species is widely known, its precise range within the Miocene has yet to be determined. Hanna (1932) has stated that it is not known from late Miocene or youn- ger deposits. Lohman (1948) reported the species from the Calvert Formation (lower to middle Miocene) of Maryland and Abbott and Andrews (1979) reported it from the Coosawhatchie Clay Member of the Haw- thorn Formation (middle Miocene). Genus CYMATOSIRA Grunow, 1862 Cymatosira belgica Grunow Plate 8, figures 4, 5 Cymatosira belgica Grunow in Van Heurck, 1881, pl. 45, figs. 38- 41; Hustedt, 1931, pp. 127-128, fig. 649; Hendey, 1964, p. 160. Description.— Valve linear-lanceolate with small, slightly produced, rounded apices. Valve surface with short, irregularly transverse rows of areolae. Hyaline central area is indistinct. Margin of valve with small spines, about seven in 10 um, projecting normal to the plane of the valves. Discussion.—The specimens observed in this study show pores scattered throughout the central area and lack the small circular hyaline area at the center of the valve. Hence, they seem to be more closely conform- able to C. belgica than to C. biharensis Pantocsek, 1889. C. belgica is frequent throughout the lower ma- rine section and rare in the upper marine bed. Known geologic range. — Not previously reported as fossil, though a related form, Cymatosira aff. C. bi- harensis, was found in the Coosawhatchie Clay Mem- ber of the Hawthorn Formation by Abbott and An- drews (1979). C. belgica is a common littoral species in temperate oceans. Cymatosira immunis (Lohman) Abbott Plate 8, figure 6 Rhaphoneis immunis Lohman, 1948, p. 182, pl. 11, fig. 6; Andrews, 1975, p. 215, pl. 3, figs. 45, 46. Cymatosira immunis (Lohman) Abbott in Abbott and Andrews, 1979, p. 242, pl. 3, fig. 18. Description. — Valve flat, lanceolate with attenuate apices. A single row of areolae alternate with spinose marginal processes, oriented perpendicular to the plane of the valves. These spinose marginal processes have T-shaped ends and interlock with similar processes on the adjacent valve in a chain of frustules, forming a positive yet flexible connection. About eight marginal areolae and eight intercalated processes in 10 um along the margin. A second row of areolae, about six in 10 um, lies parallel to and inside the marginal row and shows no ordered relationship to the marginal row. Hyaline axial area lanceolate, filling the center of the valve but not extending toward the attenuate apices. Discussion.— This distinctive species with its single row of marginal pores is rare in the 12.8 and 18.3 m (42 and 60 ft) levels of the lower marine bed. Known geologic range.—Lower to middle Miocene of the Calvert Formation of Maryland (Lohman, 1948); observed by Abbott in the Pungo River Formation of North Carolina; in the Coosawhatchie Clay Member of the Hawthorn Formation (Abbott and Andrews, 1979). Cymatosira lorenziana Grunow Plate 8, figures 7, 8 Cymatosira lorenziana Grunow, 1862, p. 378, pl. 4, fig. 25; Grunow in Van Heurck, 1881, pl. 45, fig. 42; Hustedt, 1931, p. 127, fig. 648. Description.— Valve small, flat, rounded-lanceolate with long narrowly protracted apices. Surface of valve covered with relatively large round areolae, about four in 5 um, with a primary orientation in continuous transverse rows and a secondary orientation parallel to the margin of the valve. No hyaline central or axial areas. Discussion.—A small but distinctive species, ob- served as rare in the 18.3 m (60 ft) level of the lower marine section. Known geologic range.— Reported by Schrader and Fenner (1976) from lower Miocene deposits in the Norwegian Sea. A common coastal form in Recent warmer marine waters. Genus DEBYA Pantocsek, 1886 Debya insignis Pantocsek Plate 12, figure 3 Debya insignis Pantocsek, 1886, p. 65, pl. 29, fig. 298; Pantocsek, 1889, p. 109; Hendey, 1964, p. 95, pl. 22, fig. 4. Description.—Valve round, with three low sub- rounded external swellings. Surface of valve covered by a network of very fine areolae, overlain on the ex- terior by a coarser network of faint siliceous ribbing. The three subrounded swellings are separated by three depressed rays extending from the center to the margin. A single labiate process is located near the marginal end of each depressed ray. The external pore connected to the labiate process shows a raised rim on the surface of the valve. Discussion. —Hendey (1964, p. 95) stated that Debya insignis is an auxospore valve of Actinoptychus senari- us (Ehrenberg, 1838) Ehrenberg, 1843; we agree that he is most probably correct. The affinities of D. insignis for A. senarius are obvious. However, a single labiate process is located marginally from the end of each depressed ray, in contrast to the normal condition of A. senarius, in which a single labiate process is centered on the margin of each externally raised sector. Debya MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 77 insignis was noted only in scanning electron micro- scope preparations from a sample near the base of the lower marine section. Known geologic range.—Originally described by Pantocsek (1886) from a Miocene deposit in Hungary. Presumably its range is the same as that of Actino- ptychus senarius. Genus DELPHINEIS Andrews, 1977 Delphineis angustata (Pantocsek) Andrews Plate 8, figures 9, 10 Rhaphoneis angustata Pantocsek, 1886, pt. 1, p. 33, pl. 11, fig. 97; pl. 30, fig. 313; Lohman, 1948, pp. 180-181, pl. 11, fig. 11; Loh- man, 1974, p. 352, pl. 5, fig. 14; Andrews, 1975, pp. 203-204, pl. 1, figs. 5, 6; Andrews, 1976, p. 20, pl. 7, figs. 1, 2. Delphineis angustata (Pantocsek) Andrews, 1977, pp. 250-251, pl. 1, figs. 1-4; pl. 2, figs. 21, 23; pl. 3, figs. 29, 30; Andrews, 1978, pp. 389-390, pl. 5, figs. 1, 2; pl. 8, figs. 1, 2; Abbott and Andrews, 1979, p. 242, pl. 4, fig. 1. Description.— Valve linear and elongate, tapering only slightly from near center to bluntly rounded api- ces. Transverse striae short, five in 10 um, consisting of external grooves with two areolae. Pores are sec- ondarily arranged in longitudinal rows. Transverse striae parallel for almost the length ofthe valve, slightly radiate near the apices, and fine apical striae curve completely around the ends of the valve. Pairs of trans- verse striae are well aligned across the hyaline axial area. Apical ornamentation consists of two very fine pores penetrating each end of the valve and single in- ternal labiate processes arranged diagonally to the lon- gitudinal axis. Discussion. — A distinctive marker diatom, which is rare in the 10.4, 12.8, and 15.5 m (34, 42, and 51 ft) levels of the lower marine section. Known geologic range. — Reported by Andrews (1978) to range from the lower part of unit 13 of the Calvert Formation to the upper part of unit 19 of the Choptank Formation, middle Miocene of Maryland. Occurs in the Coosawhatchie Clay Member of the Hawthorn Formation (Abbott and Andrews, 1979). Delphineis novaecaesaraea (Kain and Schultze) Andrews Plate 8, figure 14 Dimeregramma novaecaesaraea Kain and Schultze, 1889, p. 74, pl. 89, figs. 1, 1b; Lohman, 1948, pp. 184-185, pl. 11, figs. 4, 5. Delphineis novaecaesaraea (Kain and Schultze) Andrews, 1977, pp. 251-252, pl. 1, figs. 8-11; pl. 2, figs. 23, 24; pl. 3, figs. 31, 32; Andrews, 1978, p. 392, pl. 5, figs. 9-11; pl. 8, fig. 7; Abbott and Andrews, 1979, pp. 242—243, pl. 4, fig. 3; pl. 7, figs. 5, 6. Description.— Valve linear, usually having a slight expansion in the center and slightly to distinctly in- flated acute apices. Transverse striae short, seven to eight in 10 um, formed by external grooves with two areolae at the base. Striae parallel, becoming radiate near the apices, where they grade imperceptibly into finer apical striae around the ends of the valve. Hyaline axial area about 2.5 to 3 um in width, and pairs of striae are aligned across it. Two very fine pores are found on each end ofthe valve as well as single internal labiate processes oriented diagonally to the longitu- dinal axis. Discussion. — A distinctive marker diatom having readily identifiable inflated acute apices. Observed as rare only in the 16.5 m (54 ft) level ofthe lower marine section. Known geologic range. — Middle Miocene, reported by Andrews (1978) from the middle of unit 12 of the Calvert Formation to the middle of unit 18 of the Choptank Formation in Maryland. Further study has suggested to Andrews that the species may range at least as high as unit 19 of the Choptank Formation. Also reported by Abbott and Andrews (1979) from the Coosawhatchie Clay Member of the Hawthorn For- mation. Delphineis penelliptica Andrews Plate 8, figures 11-13; Plate 13, figure 1 Delphineis penelliptica Andrews, 1977, pp. 253-254, pl. 1, figs. 16- 20; pl. 2, figs. 27, 28; pl. 4, figs. 35, 36; Andrews, 1978, pp. 395- 396, pl. 5, figs. 15-17; pl. 8, fig. 8. Description. — Valve elliptical-lanceolate to lanceo- late with lateral margins tapering with but slight cur- vature toward rounded apices. Transverse striae con- tain three or four areolae near the center, but only one or two near the apices. About five-and-one-half to sev- en transverse striae in 10 um, parallel in the center, but becoming slightly radiate and finer near the apices. Fine apical striae curve around the ends of the valve. Hyaline axial area narrow, up to only about 1 um in width, and pairs of transverse striae are well aligned across it. Apical ornamentation consists of two fine pores penetrating the valve and single internal labiate processes arranged diagonally to the longitudinal axis. Discussion. — A distinctive marker fossil, which is rare to frequent throughout the lower marine section. Known geologic range. — Lower to middle Miocene. From the top of unit 9 of the Calvert Formation to the middle of unit 16 ofthe Choptank Formation of Mary- land (Andrews, 1978). Genus DENTICULOPSIS Simonsen, 1979 Denticulopsis nicobarica (Grunow) Simonsen Denticula nicobarica Grunow, 1870, p. 97, pl. 1A, fig. 5; Grunow in Van Heurck, 1881, pl. 49, fig. 3; Simonsen and Kanaya, 1961, p. 503, pl. 1, figs. 11-13; Schrader, 1973a, p. 705, pl. 1, figs. 31— 35; Schrader, 1973b, pp. 419-420, pl. 1, figs. 25-27. Denticulopsis nicobarica (Grunow) Simonsen, 1979, p. 65. 78 BULLETIN 321 Description. — Valves narrowly linear to linear-ellip- tical with bluntly rounded ends. Four to five pseudo- septa in 10 um with intercalated short riblike wall thickenings that extend from valve edge to raphe, about 16 in 10 um. Secondary pseudosepta not present. Transverse rows of coarse areolae, about 16 in 10 um, arranged in quincuncial pattern. Raphe marginal. Discussion. — Observed as rare by Abbott in sample FE 105 at approximately the 12.2 m (40 ft) level in the lower marine section. Known geologic range. —Reported by Schrader (1973b) from North Pacific Diatom Zones 20 through 24, approximately early middle Miocene in age. Gom- bos (1975) observed this species in Pacific deposits from early Miocene to late middle Miocene in age. Genus DIPLONEIS Ehrenberg, 1840 Diploneis bombus (Ehrenberg) Cleve Pinnularia (Diploneis) bombus Ehrenberg, 1844, p. 84. Diploneis bombus (Ehrenberg) Cleve, 1894, p. 90; Hustedt, 1937, pp. 704—709, fig. 1086; Hendey, 1964, p. 227, pl. 32, fig. 2; Abbott and Andrews, 1979, p. 243, pl. 4, fig. 6. Description. — Valve panduriform with central con- striction dividing the valve into two suborbicular or elliptical segments. Hyaline central area longitudinally rectangular, extending into horns that enclose the raphe. The horns diverge in the middle of each segment but converge toward the apices. Valve surface covered with transverse rows of areolae alternating with costae, about eight in 10 um. The areolae show a secondary orien- tation in longitudinal rows. Discussion. — Observed as rare by Abbott throughout the lower marine section. Known geologic range.—Reported by Abbott and Andrews (1979) from the middle Miocene Coosa- whatchie Clay Member of the Hawthorn Formation. A common species in modern coastal waters. Diploneis crabro (Ehrenberg) Ehrenberg Plate 8, figures 15, 16 Pinnularia (Diploneis) crabro Ehrenberg, 1844, p. 85. Diploneis crabro (Ehrenberg) Ehrenberg, 1854, pl. 19, fig. 29; Cleve, 1894, pp. 100-102; Hustedt, 1937, pp. 616—626, fig. 1028; Hen- dey, 1964, p. 225, pl. 32, figs. 1, 3; Andrews, 1976, p. 23, pl. 7, figs. 22, 23; Abbott and Andrews, 1979, pp. 243-244, pl. 4, fig. 7. Description. — Valve panduriform with elliptical-cu- neate segments; apices obtusely rounded. Central nod- ule quadrate to slightly elongate longitudinally, ex- tended to form siliceous horns on either side of the raphe. A row of large pores borders very narrow fur- rows. About seven transverse striae in 10 um, radiate, consisting of double transverse rows of fine areolae alternating with costae. Discussion. — A complex species, showing much variation in external outline. Frequent throughout the lower marine section and rare in the upper marine bed. Known geologic range. — Lower to middle Miocene of Maryland to Recent (common in modern marine environments of high salinity); in the Coosawhatchie Clay Member ofthe Hawthorn Formation (Abbott and Andrews, 1979). Diploneis aff. D. suborbicularis (Gregory) Cleve Plate 8, figure 17 Navicula smithii var. suborbicularis Gregory, 1857, p. 487, pl. 9, fig. qu À Diploneis suborbicularis (Gregory) Cleve, 1894, p. 81; Hustedt, 1937, pp. 612-613, fig. 1026; Hendey, 1964, p. 224. Description. — Valve broadly elliptical or oblong el- liptical with rounded apices and almost parallel sides. Central nodule quadrate, extended into two curved horns on either side ofthe raphe. Furrows linear, crossed by a faint continuation of the costae that ornament the valve surface. Costae about six to eight in 10 um, par- allel in the middle but radiating toward the apices. Discussion. — This form seems to conform with D. suborbicularis in most respects, but the ends are some- what more blunt than those shown in the figures of Hustedt (1937). Frequent in the 12.8 m (42 ft) level and rare in the 15.5 and 16.5 m (51 and 54 ft) levels of the lower marine section. Known geologic range.—Not previously reported as a fossil. À common shallow marine species in Recent warm to temperate waters. Genus ENDICTYA Ehrenberg, 1845b Endictya oceanica Ehrenberg Plate 8, figure 18 Endictya oceanica Ehrenberg, 1845b, p. 76; Ehrenberg, 1854, pl. 35A, XVIII, figs. 6, 7; Hustedt, 1928, pp. 297-299, fig. 136; Hen- dey, 1964, p. 82; Abbott and Andrews, 1979, p. 244, pl. 4, fig. 10. Description. —Frustules cylindrical with large flat circular valves and a relatively wide perpendicular mantle. Observed in this deposit only as large mantle fragments with straight sides and covered with rela- tively fine areolae in transverse straight lines. Discussion. — Occurs intermittently as rare frag- ments in the lower marine section and was observed in the upper marine bed. Known geologic range. — Previously reported from the Coosawhatchie Clay Member of the Hawthorn For- mation by Abbott and Andrews (1979). Widespread in modern oceans. MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 79 Genus GRAMMATOPHORA Ehrenberg, 1841 Grammatophora marina (Lyngbye) Kützing Plate 8, figure 20 Diatoma marinum Lyngbye, 1819, pl. 62A. Grammatophora marina (Lyngbye) Kützing, 1844, p. 128, pl. 17, figs. XXIV, 1-6; pl. 18, figs. I, 1-5; Hustedt, 1931, pp. 43-44, fig. 569; Hendey, 1964, p. 170; Andrews, 1976, p. 22, pl. 7, figs. 14, 15; Abbott and Andrews, 1979, p. 245, pl. 4, fig. 14; Andrews, 1980, p. 30, pl. 2, fig. 14. Description. — Valve elongate with bluntly rounded apices. Fine structure not usually preserved. Robust internal septa are nearly flat. Single elliptical central Opening is the most striking feature of the valve. Discussion. —Intermittently of rare occurrence in the lower marine section. Known geologic range.—Miocene to Holocene; a benthic form common in modern oceans. Genus GYROSIGMA Hassall, 1845 Gyrosigma species Plate 8, figure 19 Description.— Valve sigmoid-lanceolate tapering to narrowly rounded apices. Surface of valve covered with very fine areolae, arranged in both transverse and lon- gitudinal rows. Raphe thin, in center of the valve through most of its length but skewed toward the con- cave sides of the sigmoidally flexed ends. Hyaline cen- tral area small, irregular in outline. Discussion.—This form of Gyrosigma was rare in the 12.8 m (42 ft) level of the lower marine bed. It could not be readily identified with any described species, and the few specimens observed did not justify formal taxonomic treatment. Known geologic range.— Until this form can be spe- cifically identified, it must be considered as known only from this deposit. Genus HEMIAULUS Ehrenberg, 1844 Hemiaulus ambiguus Grunow Hemiaulus ambiguus Grunow, 1884, p. 62, pl. 2, figs. 25, 26; Hu- stedt, 1930, pp. 876-877, fig. 520. Description. — Valve irregularly elliptical-lanceolate with apices terminating in prominent horns, normal to the plane of the valves. Central part of valve shows a slight swelling. Valve surface covered with irregularly radiating rows of fine areolae, about nine to 10 in 10 um, extending from the face of the valve to the mantle. Apical horns show a short curved spine on ends. Discussion. — Observed by Abbott as rare in the 18.3 m (60 ft) and the 12.2 m (40 ft) levels and frequent in the 10.4 m (34 ft) level of the lower marine section. Known geologic range.—Previously reported only from modern arctic marine environments. Hemiaulus bipons (Ehrenberg) Grunow Plate 8, figures 21, 22 Zygoceros bipons Ehrenberg, 1845a, p. 273. Hemiaulus bipons (Ehrenberg) Grunow in Van Heurck, 1882, pl. 103, figs. 6-9; Lohman, 1948, p. 177, pl. 10, fig. 7; Lohman, 1974, p. 348. Description.— Valve elliptical and moderately con- vex, with apices extended to a small sharp point. Sur- face of valve covered with large pores distributed ir- regularly. Length of observed specimens, 32 to 35 um; width about 18 um. Interior of valve has two transverse septa, each located about halfway between the center and respective ends of the valve. These septa are some- times warped and not always oriented in an exactly transverse direction. Discussion. —Intermittently rare in the lower marine section. Known geologic range.—Lohman (1948) reported this species as occurring in the Miocene Calvert For- mation of Maryland and ranging into modern arctic marine environments. Hemiaulus polymorphus Grunow Hemiaulus polymorphus Grunow, 1884, p. 66; Hustedt, 1930, pp. 880-881. Description.— Valve usually oriented in girdle view, with a single slightly bulbous center and two prominent tubular apical horns. Bulbous central part divided from ends of valve by two internal transverse septa. Mantle and horns of valve covered with irregularly radial rows of areolae. Discussion. —Observed by Abbott as frequent in sample FE 100 and rare in sample FE 104, approxi- mately the 18.3 and 13.1 m (60 and 43 ft) levels, of the lower marine section. Known geologic range.— A variety of H. polymor- phus was reported by Grunow (1884) from lower Eocene deposits in Denmark and by Abbott and Andrews (1979) from the middle Miocene Coosawhatchie Clay Member of the Hawthorn Formation. It is known from modern arctic marine waters. Genus HYALODISCUS Ehrenberg, 1845b Hyalodiscus scoticus (Kiitzing) Grunow Plate 8, figure 23 Cyclotella scotica Kützing, 1844, p. 50, pl. 1, figs. 2, 3. Hyalodiscus scoticus (Kützing) Grunow, 1879, p. 690, pl. 21, fig. 5; Hustedt, 1928, pp. 293-294, fig. 133; Hendey, 1964, p. 90; An- drews, 1980, pp. 30-31, pl. 2, fig. 11. Description. — Valve round, convex, with center flat- tened or slightly depressed. Surface of valve shows a roughly circular umbilicus at about half the radius. Valve covered with fine areolae, but pattern and spac- 80 BULLETIN 321 ing were too fine to resolve under the light microscope. Narrow marginal rim is finely striate. Discussion. — Rare throughout the lower marine sec- tion and frequent in the marine beds immediately above and below the nonmarine strata. Known geologic range.—Reported by Andrews (1980) from the upper Miocene or lower Pliocene de- posit at Petersburg, Virginia. Reported from Holocene marine and brackish-water environments. Genus LIRADISCUS Greville, 1865 Liradiscus bipolaris Lohman Plate 8, figure 24 Liradiscus bipolaris Lohman, 1948, p. 164, pl. 7, fig. 5; Abbott and Andrews, 1979, p. 245, pl. 4, fig. 19. Description.— Valve oblong with broadly rounded ends, sometimes slightly concave along lateral mar- gins. Surface of valve nearly flat, but showing two low raised areas from which radiate curved to linear anas- tomosing markings that form an irregular network. In- terspaces between markings are hyaline. Discussion.— Rare in the 16.5 m (54 ft) level of the lower marine section. Known geologic range.—Originally described by Lohman (1948) from the lower to middle Miocene Calvert Formation of Maryland. Reported by Abbott and Andrews (1979) from the Coosawhatchie Clay Member of the Hawthorn Formation. Genus LITHODESMIUM Ehrenberg, 1840 Lithodesmium ehrenbergii (Grunow) Forti Plate 8, figure 25 Triceratium (Ditylium?) ehrenbergii Grunow in Van Heurck, 1883, pl 145, figs. 7; 8. Lithodesmium ehrenbergii (Grunow) Forti, 1912, p. 83; Forti, 1913, pp. 1613-1614. Description. — Valve rounded-triangular with round- ed obtuse angles. Surface of valve covered with radial rows of areolae, about 14 in 10 um. Small irregular hyaline areas at the angles and a large irregular hyaline central area. Single large “punctum” at center of valve is probably a labiate process that cannot be resolved under the light microscope. Discussion. — Rare in the 18.3 m (60 ft) level of the lower marine section. Known geologic range. — Originally described by Grunow in Van Heurck, 1883 from the lower Miocene part of the Calvert Formation at Nottingham, Mary- land. Reported by Forti (1912) from middle Miocene limestone in Italy. Lithodesmium undulatum Ehrenberg Plate 8, figure 26 Lithodesmium undulatum Ehrenberg, 1841, p. 155, pl. 4, fig. 13; Grunow in Van Heurck, 1883, pl. 116, figs. 8-11; Hustedt, 1930, pp. 789—791, fig. 461; Hendey, 1964, p. 111, pl. 6, fig. 6; Abbott and Andrews, 1979, p. 246, pl. 4, fig. 21. Description. — Valve triangular, each side with a median swelling forming an undulate margin. This me- dian swelling is caused by a more or less circular central part of the valve being separated from the angles by indentations in the valve surface. Angles are bluntly rounded. Valve covered with radiate rows of areolae, about 10 rows in 10 um. Valve mantle sharply deflected from surface and relatively wide. Small hyaline central area with a centered prominent “punctum”, which is probably a labiate process that cannot be resolved un- der the light microscope. Discussion. — Rare in the 18.3 m (60 ft) level of the lower marine section. Known geologic range.—Reported by Abbott and Andrews (1979) from the middle Miocene Coosa- whatchie Clay Member of the Hawthorn Formation. A common neritic species in warmer modern coastal waters. Genus MELOSIRA Agardh, 1824 Melosira westii Smith Plate 8, figure 27 Melosira westii Smith, 1856, p. 59, pl. 52, fig. 333; Hustedt, 1927, pp. 268-269, fig. 113; Hendey, 1964, p. 73, pl. 1, fig. 4; pl. 22, fig. 8; Andrews, 1976, p. 8, pl. 1, figs. 1, 2; Abbott and Andrews, 1979, p. 246, pl. 4, fig. 23; Andrews, 1980, p. 31, pl. 2, fig. 15. Description.— Valve disciform with heavy mantle, rarely seen because of common orientation in valve view. Immediately inside the mantle rim is a row of very short, fine striae. Center of valve dominated by relatively large, irregularly distributed blobs of silica showing a patchy appearance. Discussion. —Intermittently rare to frequent through the lower marine section. Known geologic range. — Cretaceous to Holocene ac- cording to Fenner (1977); modern occurrence in ma- rine coastal waters. Genus NAVICULA Bory, 1822 Navicula arenaria Donkin Plate 8, figures 28, 29 Navicula arenaria Donkin, 1861, p. 10, pl. 1, figs. 8, 9; Hendey, 1964, p. 196, pl. 30, fig. 15. Description. — Valve small, lanceolate, with subacute apices. Axial area narrow, indistinct with small, ill- defined, rounded central area. Transverse rows of ar- MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 81 eolae about nine to 10 in 10 um, radiate in the middle of the valve to transverse or slightly convergent toward the apices. Discussion. — Observed as rare at the 12.8 m (42 ft) level of the lower marine section. Known geologic range.— Not previously reported as a fossil. A marine littoral species in modern oceans and tolerant of a considerable range in salinity. Navicula maculata (Bailey) Edwards Plate 8, figure 30 Stauroneis maculata Bailey, 1850, p. 40, pl. 2, fig. 32. Navicula maculata (Bailey) Edwards, 1860, p. 128; Hustedt, 1966, pp. 707-711, fig. 1698. Description. — Valve broadly elliptical with rounded, slightly subrostrate apices. Transverse rows of large round areolae, about seven in 10 um, divergent throughout the length of the valve, secondarily ar- ranged in irregular longitudinal rows. Hyaline axial area narrow. Hyaline central area moderately large, subround to transversely elliptical. Discussion.— Rare in both the 18.3 m (60 ft) level of the lower marine section and the upper marine bed. Known geologic range. — Hustedt (1966, p. 710) re- ported the occurrence of this taxon as: "Especially widespread and common in brackish and sea water on the Atlantic coast of America. In the European region not observed in the Recent, found as fossil in Hungary and Italy." This is a curious distribution, suggesting that perhaps N. maculata may be a fossil species re- worked from Miocene deposits along the east coast of the United States into modern marine sediments. Genus NITZSCHIA Hassall, 1845 Nitzschia species A Plate 8, figures 31, 32 Description. — Valve smoothly lanceolate with point- ed apices and only a trace of central constriction. Length of observed specimens, 53 to 62 um, width about 10 um. Either the surface of valve is hyaline or the rows Of pores are too fine to be resolved under the light microscope. About eight marginal keel puncta in 10 um. Discussion.—If the valves are indeed hyaline, this form may be related to Nitzschia imperforata Andrews, 1980, described from Neogene strata in Virginia. This form is definitely not N. imperforata, however, and because of its scarcity, formal taxonomic treatment is not here attempted. This species of Nitzschia is rare in the 12.8 and 16.5 m (42 and 54 ft) levels of the lower marine section. Known geologic range. — Known only from this de- posit. Genus PARALIA Heiberg, 1863 Paralia complexa (Lohman) Andrews Plate 8, figure 33 Melosira complexa Lohman, 1948, p. 156, pl. 5, figs. 1-7. Paralia complexa (Lohman) Andrews, 1976, p. 8, pl. 1, figs. 3, 4; Abbott and Andrews, 1979, p. 247, pl. 4, fig. 26. Description. — Valve round, convex. Ornamentation varies in concentric zones: outer zone dominated by highly irregular but generally radiate striae; second zone by a ring of concentric areolae; third zone, 3 to 5 um wide, with fine pores arranged in a quincuncial pattern. Center of valve highly convex, with many irregularly distributed large areolae; at selected focus, it may also show radiate striae. Discussion. — Noted as rare in the 13.7 and 18.3 m (45 and 60 ft) levels of the lower marine section and in the upper marine bed. Known geologic range. — Lower to middle Miocene. Reported by Abbott and Andrews (1979) in the middle Miocene Coosawhatchie Clay Member of the Haw- thorn Formation. Paralia sulcata (Ehrenberg) Cleve Plate 9, figure 1 Gaillonella sulcata Ehrenberg, 1838, p. 170, pl. 21, fig. 5. Paralia sulcata (Ehrenberg) Cleve, 1873, p. 7; Hendey, 1964, p. 73, pl. 23, fig. 5; Andrews, 1976, pp. 8-9, pl. 1, figs. 5, 6; Abbott and Andrews, 1979, p. 247, pl. 4, figs. 27, 28; Andrews, 1980, pp. 31- 32 pl 2 tee 23% Melosira sulcata (Ehrenberg) Kützing, 1844, p. 55, pl. 2, fig. 7; Hu- stedt, 1928, pp. 276-279, fig. 119; Lohman, 1941, p. 64, pl. 12, fig. 1; Lohman, 1948, pp. 156-157. Description.— Valve round, nearly flat. Outer rim complexly loculate with about five chambers in 10 um. Rim is succeeded inwardly by a narrow band of fine pores, about 14 in 10 um, arranged in a quincuncial pattern, then by a hyaline band less than 1 um in width, then by a ring of prominent radial striae, about 10 in 10 um, which taper toward the hyaline center. Discussion. — Frequent to common in all the marine strata studied for this report. Known geologic range.—A variety as old as Creta- ceous is known (Lohman, 1948), and the species ranges throughout the Tertiary and Quaternary to a common occurrence in Holocene marine coastal waters. P. sul- cata and the related variety, P. sulcata var. coronata (Ehrenberg, 1845c) Andrews, 1976, are the most com- mon marine diatoms to be found in the Cenozoic de- posits of the Atlantic Coastal Plain. They seem to be relatively resistant to dissolution and are sometimes the only identifiable diatoms in a poorly preserved assemblage. Although valuable as indicators of marine deposition, their long range makes them useless for correlation or age determination. 82 BULLETIN 321 Paralia sulcata var. coronata (Ehrenberg) Andrews Plate 9, figure 2 Gaillonella coronata Ehrenberg, 1845c, p. 154, pl. 38, XXII, fig. 5. Paralia sulcata var. coronata (Ehrenberg) Andrews, i976, p. 9, pl. 1, figs. 7, 8; Abbott and Andrews, 1979, pp. 247-248, pl. 4, fig. 29; Andrews, 1980, p. 32, pl. 3, fig. 1. Melosira (Paralia) sulcata var. coronata (Ehrenberg) Grunow in Van Heurck, 1882, pl. 91, fig. 17. Melosira sulcata forma coronata Grunow. Hustedt, 1928, p. 278, fig. 119d. Description.—Valve round, nearly flat. Outer rim complexly loculate, similar to that of the typical va- riety, succeeded inwardly by a hyaline band about 2 um in width, then by a ring of knobby and irregular siliceous processes, three to four in 10 um, directed outward from a broad, flat hyaline center. Discussion. — Frequent to common in all the marine strata studied for this report. Recent research suggests that this variety is the separation valve and that the typical variety is the linking valve in chains of frustules of the same diatom. Known geologic range. — Same as the typical variety. Genus PERIPTERA Ehrenberg, 1845a Periptera petiolata Andrews Plate 9, figure 3 Periptera petiolata Andrews in Abbott and Andrews, 1979, pl. 4, figs. 30-34; pl. 8, fig. 1. Description.—Valve usually seen in girdle view, roughly rectangular in outline, but prominently flexed at both apices and the center. A single row of areolae, about six to eight in 10 um, is irregularly spaced along one flexed margin. On the same side of the valve, extending from the center is a prominent projection or boss, eight to 10 um high, tapering slightly from the valve surface to a flat top with a narrow flange around it. Discussion. — Observed as rare in the 8.8 and 18.3 m (29 and 60 ft) levels of the lower marine section. This is probably a diatom spore, but the diatom to which it pertains has not yet been identified. Known geologic range. —Previously reported only from the middle Miocene Coosawhatchie Clay Mem- ber of the Hawthorn Formation by Abbott and An- drews (1979). Genus PLEUROSIGMA Smith, 1852 Pleurosigma aff. P. aestuarii (Brébisson) Smith Plate 9, figures 4, 5 Navicula aestuarii Brébisson in Kützing, 1849, p. 890. Pleurosigma aestuarii (Brébisson) Smith, 1853, p. 65, pl. 31, fig. 275; Hendey, 1964, p. 247, pl. 36, fig. 5; pl. 41, fig. 5. Description. — Valve lanceolate to broadly lanceolate with a gently sigmoid outline. Ends attenuate, ending in sharply rounded apices. Raphe considerably more sigmoid than the valve margin, central in the middle of the valve, but close to the margin near the apices. Valve surface covered by very fine areolae, arranged in both transverse and oblique rows. Axial area narrow; central area small, rounded. Discussion.—Appears to be close to P. aestuarii, though the apices are somewhat more attenuate and the ends of the raphe are closer to the margin than are those in the specimen illustrated by Hendey (1964, pl. 36, fig. 5). The form is rare in most of the samples from the lower marine section. Known geologic range.—P. aestuarii has not previ- ously been reported as a fossil. A common species in temperate marine coastal waters of modern oceans. Genus PYRGUPYXIS Hendey, 1969 Pyrgupyxis johnsoniana Hendey Plate 9, figure 6 Pyrgupyxis johnsoniana Hendey, 1969, p. 3. Pyxilla johnsoniana Grove and Sturt, 1887, p. 71, pl. 5, fig. 10 (non Greville, 1865); Laporte and Lefébure, 1929, pl. 7, fig. 48. Description. — Valve usually seen in girdle view, cy- lindrical in shape. Base straight, extending to a slightly bulbous main part of valve, extending upward into a long, hollow horn. This horn has a single siliceous spine directed outward from the end. Valve covered with irregular radial rows of areolae, about seven to eight in 10 um, finer on the projecting horn. Discussion.—This form seems to be identifiable as P. johnsoniana, although the published figures cited above do not show the spine at the end of the apical horn. The species was noted as rare in the 12.8 m (42 ft) level of the lower marine section and also observed as rare by Abbott in sample FE 104 at approximately the 13.1 m (43 ft) level. Known geologic range.—Reported by Grove and Sturt (1887) from the upper Eocene deposit at Oamaru, New Zealand. Not previously known from Miocene strata in the southeastern United States. Genus RHAPHONEIS Ehrenberg, 1844 Rhaphoneis adamantea Andrews Plate 9, figures 7, 8; Plate 13, figures 2, 3 Rhaphoneis adamantea Andrews, 1978, pp. 384-385, pl. 2, figs. 9- iL Description.— Valve lozenge-shaped with obtusely rounded lateral margins and narrowly rounded, some- times slightly produced apices. Transverse rows of large, round areolae, about three to four in 10 um, parallel in the center to slightly radiate near the apices. Areolae show a secondary arrangement in slightly curved lon- gitudinal rows. Transverse rows of areolae not aligned across the very narrow hyaline axial area. A single i | | H | MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 83 labiate process subcentered in each end of the valve. Pseudocellus consists of a small field of fine pores at the very tip of the valve. Vela supported by two struts and show a roughly concentric pattern of fine openings. Discussion. — Rare to frequent throughout the lower marine section. Known geologic range.—Reported by Andrews (1978) from the middle part of lithologic unit 11 to the upper part of lithologic unit 13 of the Calvert For- mation (upper lower to lower middle Miocene) of Maryland. Rhaphoneis elegans (Pantocsek and Grunow) Hanna Plate 9, figures 9, 10; Plate 13, figure 4 Rhaphoneis gemmifera var. elegans Pantocsek and Grunow in Pan- tocsek, 1886, pt. 1, p. 34, pl. 2, fig. 21; pl. 20, fig. 179; pl. 27, fig. 264; pl. 30, fig. 317. Rhaphoneis elegans (Pantocsek and Grunow) Hanna, 1932, p. 213, pl. 15, figs. 6-8; Lohman, 1948, p. 182, pl. 11, fig. 2; Lohman, 1974, p. 353, pl. 6, fig. 1; Andrews, 1975, p. 208, pl. 2, figs. 25- 27; Andrews, 1978, p. 386, pl. 3, figs. 10, 11. Description.— Valve subrhomboid with obtusely rounded lateral margins at center and elongate, pro- tracted apices. Areolae large, arranged in slightly ra- diating transverse rows, five in 10 um. Areolae show secondary orientation in somewhat poorly organized longitudinal rows. Hyaline axial area 1.5 to 2 um wide at center, narrowing toward the apices. Transverse rows of areolae not aligned across the axial area. Apical pseudonodulus consists of transverse rows of fine pores. Discussion.—Rare in the 13.7 and 15.5 m (45 and 51 ft) levels of the lower marine section. Known geologic range.—Reported by Andrews (1978) from the lower part of lithologic unit 14 of the Calvert Formation (lower middle Miocene) in Mary- land. Rhaphoneis fusiformis Andrews Plate 9, figures 11-13; Plate 13, figure 5 Rhaphoneis fusiformis Andrews, 1978, p. 386, pl. 3, figs. 14-16. Description. —Valve lanceolate with smoothly rounded lateral margins. Apices protracted, narrowly rounded to bluntly pointed, somewhat asymmetrical and often slightly bent in relation to the longitudinal axis. Five to six transverse rows of large, relatively few areolae in 10 wm. Hyaline axial area narrow, and rows of areolae are not aligned across it. Apical fine struc- tures not observed. Discussion. — Rare to frequent throughout the lower marine section, except for the uppermost and lower- most beds. Known geologic range.—Reported by Andrews (1978) from the upper part of lithologic unit 3 to the middle of unit 11 in the Calvert Formation (upper lower Miocene) of Maryland. Rhaphoneis magnapunctata Andrews Plate 9, figures 14-16; Plate 13, figure 7 Rhaphoneis magnapunctata Andrews, 1978, pp. 387-388, pl. 4, figs. 1-4; pl. 7, fig. 2. Description.— Valve large, variable in shape from subrhomboidal to narrowly lanceolate with protracted attenuate apices. Ends of valve very narrowly rounded. Transverse rows of areolae three to four in 10 um, parallel, composed of very large areolae with a sec- ondary arrangement in slightly wavy longitudinal lines. Although the areola spacing remains constant except at the very tip of the valve, in large specimens the pores increase in size toward the attenuate apices. Valves sometimes slightly asymmetrical longitudinally and a bit bent near the apices. Hyaline axial area nar- row and transverse rows of areolae not aligned across it. Single internal labiate process on each end of valve. Pseudocellus consists of a small field of fine pores at the tip of the valve. Discussion. — Frequent throughout the lower marine section but rare in the uppermost bed. Known geologic range.—Reported by Andrews (1978) from lithologic unit 10 through the lower part of unit 14 of the Calvert Formation (upper lower to lower middle Miocene) of Maryland. Rhaphoneis parilis Hanna Plate 9, figures 17-19; Plate 13, figure 6 Rhaphoneis parilis Hanna, 1932, p. 214, pl. 16, figs. 2-4; Lohman, 1948, p. 182, pl. 11, fig. 10; Andrews, 1975, pp. 214-215, pl. 3, figs. 41-44; Andrews, 1978, p. 388, pl. 3, figs. 22, 23; pl. 7, fig. 3. Description.— Valve narrowly lanceolate, long and slender, tapering to protracted apices and with very obtusely rounded lateral margins. Transverse rows of evenly spaced areolae are straight, about six to seven in 10 um. Areolae arranged secondarily in straight lon- gitudinal rows, and valve shows a distinctly quadrate areolate pattern. Hyaline axial area very narrow, but usually distinct. Transverse rows of areolae are aligned across the axial area. The apices show pseudocelli formed of very fine pores and a single internal labiate process on each end. Discussion. — Frequent throughout the lower marine section, except for the 19.2 m (63 ft) level and a rare occurrence in the 8.8 m (29 ft) level. Known geologic range.—Reported by Andrews (1978) from the middle of lithologic unit 11 to near the top of unit 15 of the Calvert Formation (upper lower to lower middle Miocene) in Maryland. 84 BULLETIN 321 Genus RHIZOSOLENIA Ehrenberg, 1843 Rhizosolenia styliformis Brightwell Rhizosolenia styliformis Brightwell, 1858, p. 94, pl. 5, fig. 5; Hustedt, 1929, p. 584, fig. 333; Hendey, 1964, p. 150, pl. 2, fig. 1; Abbott and Andrews, 1979, pp. 251-252, pl. 5, figs. 24, 25. Description.—Only the more heavily silicified pen- point-like tip observed in these assemblages. Apical spine is hollow with two small lateral wings at base. Tip is hyaline; center of base marked by scattered ar- eolae; wings ornamented by fine striations flaring out- ward from base. Discussion. — Observed by Abbott as rare in samples FE 104 and FE 106 at approximately the 13.1 and 10.4 m (43 and 34 ft) levels of the lower marine section. Known geologic range.—Reported by Abbott and Andrews (1979) from the middle Miocene Coosa- whatchie Clay Member of the Hawthorn Formation. It is widespread in modern marine environments. Genus ROSSIELLA Desikachary and Maheshwari, 1958 Rossiella paleacea (Grunow) Desikachary and Maheshwari Plate 9, figures 20-22 Stoschia? paleacea Grunow in Van Heurck, 1883, pl. 128, fig. 6. Rossiella paleacea (Grunow) Desikachary and Maheshwari, 1958, pp. 28-29, fig. 1. Coscinodiscus paleaceus (Grunow) Rattray, 1889, p. 597; Schrader, 1973a, p. 703, pl. 3, figs. 10-12. Cussia paleacea (Grunow) Schrader, 1974a, p. 914; Abbott and An- drews, 1979, p. 241, pl. 3, fig. 14. Bogorovia paleaceus (Rattray) Jousé, 1976, pp. 1233-1234, figs. 556. Description. — Valve flat, lanceolate with slightly at- tenuate pointed apices. Single row of large areolae, about six in 10 wm, around margins. Similar large rounded to subpolygonal pores fill the inner part of the valve and show a random orientation. No hyaline cen- tral or axial areas. Discussion. — Desikachary and Maheshwari (1958) apparently complied with the rules of nomenclature in establishing the genus Rossiella with Stoschia? pale- acea Grunow as its generotype. Despite the rather ob- scure publication of the name Rossiella, it seems ad- visable to regard both Cussia Schrader, 1974b and Bogorovia Jousé, 1973 as junior synonyms. R. pale- acea is intermittently rare or frequent in the lower marine section. Known geologic range. — Reported by Schrader (19732) from his North Pacific Diatom Zones XVI- XXIII and by Abbott and Andrews (1979) from the Coosawhatchie Clay Member of the Hawthorn For- mation. Rossiella praepaleacea (Schrader) Andrews new combination Coscinodiscus praepaleaceus Schrader, 1973a, p. 703, pl. 3, figs. 1-9. Cussia praepaleacea (Schrader) Schrader, 1974a, p. 914; Abbott and Andrews, 1979, p. 241, pl. 3, fig. 15. Description. — Valve flat, smoothly lanceolate, with pointed apices. Surface of valve areolate; strong mar- ginal ribs extend to center of valve between areolae. Transverse ribs not aligned across center of valve, but joined at center by a weak, crudely zigzag central apical rib. No central or axial area. Discussion. — Observed by Abbott as rare to frequent in samples FE 103, FE 104, FE 105, and FE 106 at approximate levels of 13.7, 13.1, 12.2, 10.4 m (45, 43, 40, and 34 ft), respectively, in the lower marine section. Known geologic range.— According to Abbott and Andrews (1979), this species is possibly restricted to the Miocene, but the first occurrence is not known with certainty. Genus SCEPTRONEIS Ehrenberg, 1844 Sceptroneis grandis Abbott Sceptroneis grandis Abbott in Abbott and Ernissee, 1983, pp. 302- 303, pl. 11, fig. 7; pl. 12, fig. 1. Description.— Valve clavate, elongate, heavily silic- ified, with a broader rounded head-pole and narrower pointed foot-pole. Valve covered with short transverse rows of areolae, not aligned across the narrow axial area. Apical structures not observed. Discussion.— Sceptroneis grandis was described by Abbott (1983) from the Pungo River Formation in North Carolina. The species was observed by Abbott as frequent in samples FE 102, FE 103 and FE 106 and rare in FE 105 at levels of approximately 15.2, 13.7, 10.4, and 12.2 m (50, 45, 34, and 40 ft), respec- tively, in the lower marine section. Known geologic range. — Atlantic Miocene Siliceous Microfossil Zones I and III of Abbott (1978) and upper lower Miocene to lower middle Miocene. Genus STEPHANOPYXIS Ehrenberg, 1844 Stephanopyxis corona (Ehrenberg) Grunow Systephania corona Ehrenberg, 1845a, p. 272; Ehrenberg, 1854, pl. 33, XV, fig. 22. Stephanopyxis corona (Ehrenberg) Grunow in Van Heurck, 1882, pl. 83 ter, figs. 10, 11; Andrews, 1976, p. 9, pl. 1, figs. 11, 12; Abbott and Andrews, 1979, p. 252, pl. 5, fig. 27. Description. — Valve round, convex, hemispherical, but markedly flattened in the center. Margin loculate, convex part of valve covered with areolae arranged in | | MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 85 an orderly hexagonal pattern. Three to four large hex- agonal areolae in 10 um. A ring of prominent thornlike siliceous spines radiates from a zone near the margin, but these spines do not extend beyond the margin. A second ring of prominent siliceous spines occurs at about half radius on the valve. Discussion.— Observed as rare by Abbott in sample FE 104 at approximately the 13.1 m (43 ft) level of the lower marine section. Known geologic range.—Calvert and Choptank For- mations (lower to middle Miocene) of Maryland and the middle Miocene Coosawhatchie Clay Member of the Hawthorn Formation (Abbott and Andrews, 1979). Stephanopyxis lineata (Ehrenberg) Forti Stephanodiscus? lineatus (= Peristephania lineata) Ehrenberg, 1854, pl. 33, XIII, fig. 22. Stephanopyxis lineata (Ehrenberg) Forti, 1912, p. 83; Forti, 1913, p. 1547, pl. 11, figs. 21-23; pl. 12, fig. 3; Andrews, 1976, pp. 9- 10, pl. 1, figs. 13, 14; Abbott and Andrews, 1979, p. 252, pl. 5, fig. 28. Description. — Valve round, almost flat to slightly domed. Surface of valve shows generally regular hex- agonal net of areolae, about four-and-one-half in 10 um. Margin loculate, and a ring of thornlike siliceous spines, somewhat irregularly spaced, occurs 2 to 3 um inward from the outer margin. Discussion. — Observed as frequent by Abbott in sample FE 104 at approximately the 13.1 m (43 ft) level of the lower marine section. Known geologic range. — Koizumi (1973, fig. 10) in- dicated that this species ranges throughout the middle Miocene. It has been reported in the Choptank For- mation of Maryland and the Coosawhatchie Clay Member of the Hawthorn Formation of South Caro- lina and Georgia, both of middle Miocene age. Stephanopyxis turris (Greville) Ralfs Plate 9, figure 23 Creswellia turris Greville in Gregory, 1857, p. 538, pl. 14, fig. 109. Stephanopyxis turris (Greville) Ralfs in Pritchard, 1861, p. 826, pl. 5, fig. 74; Hendey, 1964, p. 92; Abbott and Andrews, 1979, pp. 252—253, pl. 6, figs. 1, 2; pl. 8, fig. 6; Andrews, 1980, p. 34, pl. 3, fig. 15. Stephanopyxis turris (Greville and Arnott) Ralfs; Hustedt, 1928, pp. 304-307, fig. 140; Lohman, 1948, p. 185; Andrews, 1976, p. 10, pl 2 hos 1525 Description. — Valve round, highly domed. Height usually greater than diameter, hence more often seen in girdle view. Valve shows flat or slightly concave base, expanded into a narrow flange, then tapering to almost parallel sides, arching over the top as a rounded or flattened dome. Surface of valve covered with a somewhat irregular hexagonal net of areolae, four to six in 10 um. Bases of siliceous spines on domed end are commonly present. Discussion.— The valves observed in this deposit seem to be more nearly hemispherical than some de- scribed specimens, and many lack distinct spines. Per- haps some of these forms might be classified as Pyxi- dicula cruciata Ehrenberg, 1843, but most seem to be closer to S. turris. Intermittently rare in the lower ma- rine section. Known geologic range.—From Cretaceous to Ho- locene; frequent pelagic occurrence in modern marine environments. Genus STICTODISCUS Greville, 1861 Stictodiscus kittonianus Greville Plate 9, figure 27 Stictodiscus kittonianus Greville, 1861, pp. 79-80, PITO figs 2, 3: Schmidt, 1882, pl. 74, figs. 16-18; Hanna, 1932, p. 219; pl: 16, fig. 12; Lohman, 1948, pp. 167-168, pl. 9, fig. 2; Abbott and Andrews, 1979, p. 253, pl. 6, fig. 3. Description. — Valve irregularly round and markedly umbonate. Surface of valve covered with irregularly radial rows ofareolae, about eight in 10 um. Each group of two or three rows of pores separated by a siliceous ray extending from the margin part way to the center. Areolae cover center of valve in an unorganized pat- tern. Narrow hyaline marginal rim. Discussion. — Observed as rare in the 17.4 m (57 ft) level of the lower marine section. Known geologic range. — Lower to middle Miocene, including the Coosawhatchie Clay Member of the Hawthorn Formation, according to Abbott and An- drews (1979). Genus SYNEDRA Ehrenberg, 1832 Synedra jouseana Sheshukova-Poretskaya Synedra jouseana Sheshukova-Poretskaya, 1962, p. 208, fig. 4; Schrader, 1973a, p. 710, pl. 23, figs. 21-23, 25, 38. Description. — Valve narrow, lanceolate with acute apices. Transverse striae 12 to 13 in 10 um, originating in marginal areolae and projecting 2 to 3 um into valve. Axial area hyaline, very wide, lanceolate, divided into three parts by two longitudinal lines. Discussion. — Observed by Abbott as rare to frequent throughout the lower marine section. The species is difficult to distinguish from Thalassionema obtusum (Grunow in Van Heurck, 1881) Andrews, 1976. Known geologic range. —Reported by Schrader (1973a) from his North Pacific Diatom Zones XVII to XXIV, of middle to late Miocene age. Reported by Schrader and Fenner (1976) from upper Oligocene to lower Miocene deposits in the Norwegian Sea. 86 BULLETIN 321 Genus THALASSIONEMA Grunow in Van Heurck, 1881 Thalassionema nitzschioides (Grunow) Hustedt Plate 9, figure 24 Synedra nitzschioides Grunow, 1862, p. 403. Thalassionema nitzschioides (Grunow) Hustedt, 1932, pp. 244-246, fig. 725; Hendey, 1964, p. 165; Abbott and Andrews, 1979, p. 253, pl. 6, fig. 11; Andrews, 1980, p. 34, pl. 3, fig. 17. Description.—Valve narrowly linear, with almost parallel sides tapering only slightly toward bluntly rounded apices. Valve marked with a single row of marginal areolae, 10 to 11 in 10 um. Hyaline axial area covers most of valve surface. Discussion. —Rare through most of the lower marine section. Known geologic range.—A long-ranging species, at least from Miocene to Holocene. A common and wide- spread neritic species in modern coastal waters. Thalassionema obtusum (Grunow) Andrews Plate 9, figure 25 Thalassiothrix? nitzschioides var. obtusa Grunow in Van Heurck, 1881, pl. 43, fig. 6. Thalassionema obtusum (Grunow) Andrews, 1976, p. 21, pl. 7, figs. 6-8; Abbott and Andrews, 1979, p. 253, pl. 6, fig. 11. Description.—Valve narrowly lanceolate with rounded apices. A single row of areolae, about nine- and-one-half to 11 in 10 wm along the margin of the valve. Wide hyaline lanceolate axial area fills the cen- ter. Discussion. — Rare in the 12.8 m (42 ft) level of the lower marine section. Known geologic range. — Middle Miocene, including the Coosawhatchie Clay Member of the Hawthorn For- mation, as reported by Abbott and Andrews (1979). Genus THALASSIOSIRA Cleve, 1873 Thalassiosira eccentrica (Ehrenberg) Cleve Plate 9, figure 28 Coscinodiscus eccentricus Ehrenberg, 1841, p. 146; Ehrenberg, 1854, pl. 18, fig. 32; pl. 21, fig. 6; Hendey, 1964, pp. 80-81, pl. 24, fig. 7. Thalassiosira eccentrica (Ehrenberg) Cleve, 1904; Fryxell and Hasle, 1972, pp. 297-317, pls. 1-4; Abbott and Andrews, 1979, p. 254, pl, 6, fig. 12; Andrews, 1980, pp. 34-35, pl. 3, fig. 16. Coscinodiscus excentricus Ehrenberg. Hustedt, 1928, pp. 388-391, fig. 201; Lohman, 1941, pp. 67-68, pl. 12, fig. 7; pl. 13, fig. 8; Lohman, 1948, p. 161. Description. — Valve round, flat or nearly so. Valve covered by an areolate net showing a regular hexagonal pattern over much of the valve. This net is disordered somewhere on the valve by a single areola surrounded by seven, rather than six, areolae. Areolae about four- and-one-half in 10 wm, round, very even in size and spacing. Valve shows a narrow, finely granular margin. Discussion. — Rare throughout most of the lower ma- rine section. Known geologic range.—From the Calvert Forma- tion (lower and middle Miocene) in Maryland to a common and widespread occurrence in modern neritic plankton. Thalassiosira leptopus (Grunow) Hasle and Fryxell Plate 9, figures 29, 30 Coscinodiscus (lineatus var.?) leptopus Grunow in Van Heurck, 1883, pl. 131, figs. 5, 6. Thalassiosira leptopus (Grunow) Hasle and Fryxell, 1977, pp. 20- 22, pls. 1-4; pl. 18, figs. 94-96. Coscinodiscus lineatus Ehrenberg, 1838, p. 129; Ehrenberg, 1854, pl. 18, fig. 33; pl. 22, fig. 6; pl. 35A, figs. XVI-3, XVII-7; Hustedt, 1929, pp. 392-394, fig. 204; Hendey, 1964, p. 76; Abbott and Andrews, 1979, p. 238, pl. 3, fig. 1. Coscinodiscus leptopus Grunow. Rattray, 1889, p. 476. Description.—Valve round, flat or nearly so. Cov- ered with an areolate net showing a regular hexagonal pattern. Areolae about five-and-one-half in 10 um, round to hexagonal, even in size and spacing. Margin is narrow and finely striate. Small spinelike processes sometimes seen along inner edge of margin. Discussion. —Rare throughout most of the lower ma- rine section. Known geologic range.—From the Calvert Forma- tion (lower and middle Miocene) of Maryland to a common and widespread occurrence in the plankton of modern oceans. Thalassiosira species A Plate 9, figure 31 Description.—Valve round, flat, slightly warped in at least some specimens. Diameter of observed spec- imen, 26 um. Surface of valve covered by a net of polygonal areolae, about six in 10 um in the radius of the valve. These areolae are oriented in an irregularly radiate pattern; many are distinctly elongate parallel to the radius of the valve. Discussion.—This form seems to resemble Thalas- siosira somewhat more than it does Coscinodiscus Eh- renberg, 1838, but too few specimens were observed to justify formal taxonomic treatment. Rare in the 16.5 m (54 ft) level of the lower marine section. Genus THALASSIOTHRIX Cleve and Grunow, 1880 Thalassiothrix longissima Cleve and Grunow Plate 9, figure 26 Synedra thalassiothrix Cleve, 1873, p. 22, pl. 4, fig. 24. Thalassiothrix longissima Cleve and Grunow, 1880, p. 108; Hustedt, 1932, p. 247, fig. 726; Lohman, 1948, p. 185; Andrews, 1976, p. 21, pl. 7, figs. 9, 10; Abbott and Andrews, 1979, p. 254, pl. 6, fig. 13; Andrews, 1980, p. 35. Description. — Valve extremely elongate and narrow, with parallel sides and bluntly rounded apices. Trans- | | | MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 87 verse rows of areolae short, marginal, about 12 in 10 um. Hyaline axial area about one-third the width of the valve, narrowing near the apices. Discussion.— Rare in the 18.3 m (60 ft) level of the lower marine section. Known geologic range.— Miocene to Holocene. Es- pecially abundant in the colder waters of modern oceans. Genus TRICERATIUM Ehrenberg, 1841 Triceratium condecorum Ehrenberg Plate 9, figure 32 Triceratium condecorum Ehrenberg, 1845a, p. 272; Grunow in Schmidt, 1882, pl. 76, fig. 28; Hustedt in Schmidt, 1959, pl. 478, figs. 14-21; Andrews, 1976, p. 18, pl. 5, figs. 18, 19; Abbott and Andrews, 1979, p. 254, pl. 6, figs. 14, 15. Triceratium interpunctatum Grunow in Schmidt, 1882, pl. 76, fig. 7; Lohman, 1948, p. 175, pl. 10, fig. 2. Description.— Valve triangular with raised rim and depressed triangular center. Sides vary from slightly concave to straight, or slightly convex. Angles vary from obtusely rounded to a rounded point. Surface of valve covered with large areolae, arranged primarily in a radial pattern and secondarily in a roughly con- centric pattern. About five areolae in 10 um near the center, somewhat more closely spaced at the margin. Radial rows of large areolae terminate inwardly with a single small pore. A pseudonodulus consisting of fine pores is found on each of the angles. Discussion.—Rare to frequent throughout most of the lower marine section. Known geologic range. — Hustedt (1959) reported this species from the upper Eocene of New Zealand. Fre- quent to common in the Calvert and Choptank For- mations (lower to middle Miocene) of Maryland. Not known from deposits younger than Miocene. Triceratium spinosum Bailey Plate 9, figures 33, 34; Plate 12, figure 4 Triceratium spinosum Bailey, 1844, p. 139, pl. 3, fig. 12; Schmidt, 1885, pl. 87, figs. 2, 3; Hustedt, 1930, pp. 804-806, fig. 467; Hendey, 1964, pp. 108-109. Description.— Valve triangular with commonly slightly concave or straight, but sometimes slightly convex, sides. Angles of the valve are produced into narrow, tapering, horn-like processes. Valve surface convex, covered with fine areolae arranged in a warped hexagonal pattern. Several spines, both short and long, are scattered over the surface of the valve. No hyaline central area. Discussion.—Intermittently rare throughout the lower marine section. Known geologic range.—Originally described by Bailey (1844) from the Neogene deposit at Petersburg, Virginia, but not observed in a later study by Andrews (1980) ofa similar deposit. A widespread and common littoral form on the coasts of warmer seas. Genus TROCHOSIRA Kitton, 1871 Trochosira spinosa Kitton Trochospira spinosa Kitton, 1871, p. 170, pl. 14, figs. 6, 7; Sheshu- kova-Poretskaya, 1967, pp. 137-138, pl. 11, figs. 6a, b; pl. 13, figs. 4a, b; Schrader, 1973a, p. 713, pl. 12, figs. 18, 19; Abbott and Andrews, 1979, p. 255, pl. 6, fig. 19. Description. —Frustules in chains connected by sev- eral short processes. Valves convex, central part flat. Processes connecting the frustules emanate from mar- gin of the flattened central part of the valve. Discussion. —Observed by Abbott as common to fre- quent throughout the lower marine section and in the upper marine bed. Usually seen in girdle view and may be readily confused with girdle orientations of Paralia sulcata (Ehrenberg, 1838) Cleve, 1873. Known geologic range.—Lower Eocene to middle Miocene. Reported by Kitton (1871) from the lower Eocene deposit at Mors, Denmark; by Schrader (1973a) from his North Pacific Diatom Zone XXIII; by Abbott and Andrews (1979) from the middle Miocene Coo- sawhatchie Clay Member of the Hawthorn Formation. Genus XANTHIOPYXIS Ehrenberg, 1845a Xanthiopyxis species Discussion. —Specimens attributable to Xanthio- pyxis were observed as frequent throughout the lower marine section and in the upper marine bed. As is common in the Miocene deposits of the southeastern United States, the forms are highly varied, mostly small, ovate or elliptical-elongate and either hyaline or show- ing varying degrees of spinosity. Each form is very rare, and because of the doubtful value of these forms to biostratigraphy, no attempt has been made to under- take their taxonomic treatment. Genus and species indeterminate Plate 9, figure 35 Description. —Elongate valves or girdle bands, mark- edly flexed in the center. Sides straight, except for flex- ure normal to the flat surface; ends rounded and slightly asymmetrical. One longitudinal row of large marginal areolae, about five-and-one-half in 10 um, on one side only. Areolae continue to the ends. Discussion. — This object is similar to the siliceous microfossil reported without taxonomic treatment by Abbott and Andrews (1979) from the Coosawhatchie Clay Member of the Hawthorn Formation of South Carolina and eastern Georgia. These objects show the same flexed shape but differ in having a single longi- tudinal row of large pores, rather than two as in the 88 BULLETIN 321 previously observed form. These objects are equally problematical in origin. They may be girdle fragments of some diatom, possibly Rhaphoneis magnapunctata Andrews, 1978. They could possibly be valves of a flexed and imperforate species of Nitzschia Hassall, 1845, the row of pores being analogous to keel puncta. However, the similar forms having two rows of pores indicate that this interpretation is unlikely. NONMARINE DIATOMS Genus ACHNANTHES Bory, 1822 Achnanthes hungarica (Grunow) Grunow Plate 10, figure 1 Achnanthidium hungaricum Grunow, 1863, p. 146, pl. 4, figs. 8a-c. Achnanthes hungarica (Grunow) Grunow in Cleve and Grunow, 1880, p. 20; Hustedt, 1933, pp. 383-384, fig. 829; Patrick and Reimer, 1966, p. 259, pl. 16, figs. 27, 28. Description. — Valve linear-elliptical to linear-lan- ceolate with bluntly rounded, slightly subrostrate api- ces. Raphe valve with narrow linear hyaline axial area. Central area a narrow stauros reaching both margins, but broadening considerably toward one margin only. Raphe very thin. Striae fine, about 24 in 10 um, slightly radiate. Rapheless valve not observed. Discussion. — The single raphid valve observed in the nonmarine assemblage seems to conform well to A. hungarica. Known geologic range. — Not, to our knowledge, pre- viously reported as fossil. This is an alkaliphilous species with widespread occurrence in modern lakes, ponds and flowing waters. Reported by Hustedt (1933) to occur in fresh and slightly saline waters. Genus CALONEIS Cleve, 1894 Caloneis westii (Smith) Hendey Plate 10, figure 12 Navicula westii Smith, 1853, p. 49, pl. 16, fig. 135. Caloneis westii (Smith) Hendey, 1964, pp. 230-231, pl. 44, figs. 5- 10; pl. 45, figs. 1-13. Navicula formosa Gregory, 1856b, p. 42, pl. 5, fig. 6. Caloneis formosa (Gregory) Cleve, 1894, p. 57; Hustedt, 1930a, pp. 232-233, fig. 350. Description. — Valve lanceolate with obtusely round- ed apices. Axial area narrowly lanceolate, irregular, with a slight asymmetric dilation at the center of the valve. Valve surface shows about 14 transverse striae in 10 um, slightly radiate throughout the length of the valve. Longitudinal lines somewhat nearer the valve margin than the raphe. Discussion. — Although the figured specimen (PI. 10, fig. 12) is somewhat more broadly lanceolate than any figured by Hendey (1964), this taxon conforms to C. westii in all other respects. Occurs frequently in the nonmarine diatom assemblage. Known geologic range. — Not, to our knowledge, pre- viously reported as a fossil. A brackish water species, known from littoral marine environments as well as saline inland waters. Genus EUNOTIA Ehrenberg, 1837 Eunotia parallela Ehrenberg Plate 10, figure 2 Eunotia parallela Ehrenberg, 1843, p. 414; Hustedt, 1932, p. 302, fig. 768; Patrick and Reimer, 1966, p. 193, pl. 10, fig. 12; Andrews, 1970, p. A12, pl. 1, fig. 24. Description. — Valve elongate, varying from almost straight to slightly arched. Ventral and dorsal margins ofthe valve very nearly parallel. Apices bluntly round- ed. Fine structures poorly preserved in this assemblage. Discussion. — A distinctive species that is rare in the nonmarine deposit. Known geologic range. — Reported by Andrews (1970, p. A12) from a Nebraska deposit of early to middle Miocene age. Common in modern cool to cold freshwaters. Eunotia pectinalis (Müller) Rabenhorst Plate 10, figure 3 Conferva pectinalis Müller, 1788, p. 91, pl. 1, figs. 4-7; Dillwyn, 1809, pl. 24. Eunotia pectinalis (Müller) Rabenhorst; Patrick and Reimer, 1966, pp. 204—205, pl. 12, figs. 8, 10. Eunotia pectinalis (Dillwyn) Rabenhorst, 1864, p. 73. Eunotia pectinalis (Dillwyn? Kützing) Rabenhorst; Hustedt, 1932, pp. 296-299, fig. 763a. Description. — Valve elongate, slightly curved. Ven- tral margin straight to slightly concave; dorsal margin straight to slightly convex, nearly parallel to ventral margin. Valve narrows to slightly bent, attenuated, rounded ends. Transverse striae 12 in 10 um, slightly finer near the end of the valve. Discussion. — Fragments of specimens referable to E. pectinalis were observed as rare in the nonmarine as- semblage. Known geologic range.—The type variety has not been previously reported as a fossil. Commonly re- corded in modern cool waters having a low mineral content. Eunotia pectinalis var. minor (Kiitzing) Rabenhorst Plate 10, figure 4 Himatidium minus Kützing, 1844, p. 39, pl. 16, fig. 10. Eunotia pectinalis var. minor (Kiitzing) Rabenhorst, 1864, p. 74; Hustedt, 1932, p. 298, figs. 763d-f; Patrick and Reimer, 1966, p. 207, pl. 12, figs. 12, 13; Andrews, 1970, pp. A12-A13, pl. 1, fig. 25 Description.— Valve elongate, ventral margin slight- ly concave, dorsal margin distinctly convex. Valve nar- rows toward ends; apices bluntly rounded. Striae 12 in 10 wm at center, where they are perpendicular to MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 89 the ventral margin; somewhat finer and slightly curved near the ends. Discussion.—E. pectinalis var. minor is rare in the nonmarine assemblage. Known geologic range.—Reported by Andrews (1970, pp. A12-A13) from a Nebraska deposit of early to middle Miocene age. Occurs in acid to circumneutral modern fresh waters but shows a greater tolerance for calcium carbonate than do many species of Eunotia. Genus GOMPHONEMA Agardh, 1824 Gomphonema affine var. insigne (Gregory) Andrews Plate 10, figure 5 Gomphonema insigne Gregory, 1856a, p. 12, pl. 1, fig. 39; Grunow in Van Heurck, 1880, pl. 24, figs. 39-41. Gomphonema affine var. insigne (Gregory) Andrews, 1970, p. A20, pl. 3, figs. 12-16; Andrews, 1971, p. E14, pl. 2, figs. 16-18; Patrick and Reimer, 1975, pp. 133-134, pl. 17, fig. 4. Gomphonema lanceolatum var. insignis (Gregory) Cleve, 1894, p. 183; Hustedt, 1930a, p. 376, fig. 701. Description. — Valve lanceolate-clavate to nearly lan- ceolate, rounded on the head-pole but somewhat more acutely pointed on the foot-pole. Hyaline axial area about one-fourth the width of the valve. Central area asymmetrical, formed by shortening of a single trans- verse row of areolae on one side of the valve. A single stigma on opposite side of valve from the shortened row of areolae. Transverse striae fine, about 10 in 10 um, composed of rows of fine areolae. Raphe thin, filamentous. Discussion. — Rare in the nonmarine deposit. Known geologic range. —Reported by Andrews (1971, p. E14) from lower Miocene deposits in Ne- braska and also by Andrews (1970, p. A20) from lower to middle Miocene deposits in Nebraska. It has a wide- spread modern occurrence in hard to circumneutral freshwaters. Genus GYROSIGMA Hassall, 1845 Gyrosigma aff. G. spencerii (Quekett) Griffith and Henfrey Plate 10, figure 6 Navicula spencerii Quekett, 1848, p. 440, pl. 0. Gyrosigma spencerii (Quekett) Griffith and Henfrey, 1856, p. 303, pl. 11, fig. 17; Patrick and Reimer, 1966, pp. 315-316, pl. 23, fig. 4. Gyrosigma spencerii (Smith) Cleve. Hustedt, 1930a, pp. 225-226, fig. 336. Description.—Valve moderately sigmoid, lanceo- late, tapering to narrowly rounded apices. Raphe ap- proximately centered throughout the length of the valve. Small longitudinally elliptical central area. Fine struc- ture not observed because of poor preservation. Discussion. — Observed as a single poorly preserved specimen that seemed to conform to G. spencerii. Known geologic range.— G. spencerii, so far as is known, has not been previously recorded as a fossil. It has been reported from modern alkaline freshwaters and is able to tolerate some salinity. Genus MELOSIRA Agardh, 1824 Melosira juergensi Agardh Plate 10, figure 7 Melosira juergensi Agardh, 1824, p. 9; Hustedt, 1927, pp. 238-240, fig. 99. Description. — Cylindrical frustules linked in chains. Valves cylindrical with rounded ends. Section through valve wall shows slight thickening toward open end, giving the frustule a distinctive, somewhat “hourglass” internal outline. Valve mantle may be finely marked but appears to be hyaline under the light microscope. Linking processes between frustules small, indistinct. Discussion.—Common in the nonmarine assem- blage. Known geologic range. — Reported as occurrring in the middle Miocene Hualapai Limestone of Arizona by Bradbury (written commun., 1983). Hustedt (1927) stated that M. juergensi is a widespread and common brackish-water species that may range into shallow ma- rine waters. Genus NAVICULA Bory, 1822 Navicula aff. N. radiosa Kützing Plate 10, figure 8 Navicula radiosa Kützing, 1844, p. 91, pl. 4, fig. 23; Hustedt, 1930a, p. 299, fig. 513; Patrick and Reimer, 1966, p. 509, pl. 48, fig. 15; Andrews, 1970, p. A16, pl. 2, fig. 15. Description. — Valve linear-lanceolate with acute, narrowly rounded ends. Valve surface with transverse rows of areolae, about 10 in 10 um, highly radiate near the center grading to parallel or slightly convergent near the apices. Hyaline axial area narrow, little or no wid- ening at center in specimens observed. Discussion.—' The transverse rows of areolae are somewhat finer and less divergent in the center of the valve than most descriptions of modern representa- tives of this taxon suggest. This species is rare in the nonmarine assemblage. Known geologic range. — Reported by Andrews (1970, p. A16) from deposits of early to middle Mio- cene in Nebraska. Common in a wide variety of mod- ern circumneutral fresh waters and tolerant of some salinity. 90 BULLETIN 321 Genus NITZSCHIA Hassall, 1845 Nitzschia hybrida Grunow Plate 10, figure 9 Nitzschia hybrida Grunow in Cleve and Grunow, 1880, p. 79, pl. 5, fig. 95; Hustedt, 1930a, p. 406, fig. 778. Description. — Valve linear with concave to nearly straight sides. End of valve asymmetrical, smoothly and broadly rounded on keel side of valve but more sharply truncated on girdle side. Surface of valve cov- ered with fine transverse striae, about 16 in 10 um. Keel puncta obscure in specimens observed. Discussion.—Specimens in this assemblage are somewhat more coarsely marked than has been re- ported for modern representatives. Occurs rarely as fragments in the nonmarine assemblage. Known geologic range.—Not known to have been reported previously from fossil deposits. It is a salt water species, known from modern coastal waters and inland saline waters. Nitzschia tryblionella var. victoriae (Grunow) Grunow Plate 10, figure 10 Tryblionella victoriae Grunow, 1862, p. 553, pl. 12, fig. 34. Nitzschia tryblionella var. victoriae (Grunow) Grunow in Cleve and Grunow, 1880, p. 69; Hustedt, 1930a, pp. 399-400, fig. 758. Description. — Valve relatively short, elliptical, with rounded ends. Surface of valve covered with robust transverse striae, about seven in 10 um. Keel puncta about 16 in 10 um. Discussion. — Occurs frequently in the nonmarine as- semblage. Known geologic range. — Not previously known as a fossil species. The most common modern occurrence is in somewhat saline waters, but the species and its varieties range into freshwater environments. Genus PINNULARIA Ehrenberg, 1843 Pinnularia brevicostata Cleve Plate 10, figure 11 Pinnularia brevicostata Cleve, 1891, p. 25, pl. 1, fig. 5; Hustedt, 1930a, pp. 329-330, fig. 609; Patrick and Reimer, 1966, p. 623, pl. 60, fig. 1; Andrews, 1970, p. A17, pl. 3, fig. 3; Andrews, 1971, p ELL pl, 188. I9. 19. Description. — Valve linear with a slight expansion at the center and rounded ends. Hyaline axial area wide, about half the width of the valve. Transverse striae short, 12 in 10 um, slightly radiate. Discussion. — Rare in the nonmarine assemblage. Known geologic range. —Reported by Andrews (1971) from the early Miocene Pine Ridge assemblage of Nebraska and also by Andrews (1970) from the early to middle Miocene Kilgore assemblage of Nebraska. Common in modern cool waters having a low mineral content. Pinnularia fusana Andrews Plate 10, figure 13 Pinnularia fusana Andrews, 1971, pp. E11-E12, pl. 1, figs. 25-27. Description. — Valve fusiform, lanceolate-elliptical with somewhat produced, rostrate apices. Ends of valve rounded. Strong transverse costae, 10 in 10 um, radiate near the center, but convergent near the apices. Hyaline axial area narrow at the apices, irregular in outline and expanding to about one-third the width of the valve by a slight lateral swelling at the central area. Raphe straight, terminating in pronounced central nodules. Discussion.—' This taxon seems to be close to the original description of P. fusana, except that the apices are much narrower, and the valve is relatively some- what narrower. Rare in the nonmarine deposit. Known geologic range. —Previously reported only from the lower Miocene Monroe Creek Sandstone at Pine Ridge, Nebraska, by Andrews (1971). Pinnularia aff. P. microstauron (Ehrenberg) Cleve Plate 10, figure 15 Stauroptera microstauron Ehrenberg, 1843, p. 423, pl. 1, fig. IV, 1. Pinnularia microstauron (Ehrenberg) Cleve, 1891, p. 28; Hustedt, 19302, p. 320, fig. 582; Patrick and Reimer, 1966, pp. 597-598, pl. 55, fig. 12; Andrews, 1971, p. E12, pl. 1, figs. 22-24. Description. — Valve linear-lanceolate, tapering to rounded apices. About nine transverse costae in 10 um, radiate at center, but becoming convergent near the apices. Hyaline axial area narrow at the ends, ta- pering to the central area where it expands to the mar- gins of the valve. Discussion. — The figured specimen (Pl. 10, fig. 15) shows little indication of rostrate apices but seems to conform reasonably well to a specimen figured by An- drews (1971, pl. 1, fig. 24). It was observed only as rare fragments in the nonmarine assemblage. Known geologic range. — Reported by Andrews (1971, p. E12) from a deposit of early Miocene age in Nebraska. Known from a variety of modern freshwater environments but is thought to prefer oligotrophic, slightly acid waters. Pinnularia torta (Mann) Patrick Plate 10, figure 14 Navicula torta Mann, 1924, p. 31, pl. 4, fig. 6. Pinnularia torta (Mann) Patrick in Patrick and Reimer, 1966, p. 634, pl. 63, fig. 3; Andrews, 1970, p. A18, pl. 3, figs. 4, 5. Pinnularia major var. asymmetrica Cleve, 1895, p. 89, pl. 1, fig. 22, MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 91 Description. — Valve linear with rounded ends and a slight lateral expansion at the center. About seven cos- tae in 10 um, radiate at the center to convergent near the apices, some flexed to an attenuated S-shape. Hya- line axial area about one-fourth to one-third the width of the valve, markedly asymmetric to the center line of the valve. Raphe about centrally located in the axial area, filamentous, oblique to the plane of the valves. Central area rounded, slightly more expanded in di- rection of deflection of the central nodules of the raphe. Discussion. — Observed as rare in the nonmarine as- semblage. Known geologic range.—Reported by Andrews (1970, p. A18) from the “Valentine Formation” (lower to middle Miocene) of Nebraska. Modern occurrence in standing acid waters of low mineral content. Genus STAURONEIS Ehrenberg, 1843 Stauroneis aff. S. salina Smith Plate 10, figure 16 Stauroneis salina Smith, 1853, p. 60, pl. 19, fig. 188; Hustedt, 1959, pp. 786-789, fig. 1133. Description.— Valve lanceolate with rounded ends. Transverse striae very fine, parallel or slightly radiate throughout the length of the valve. Hyaline axial area narrow, expanded at the center of the valve to a narrow transversely rectangular stauros extending to the mar- gins of the valve. Discussion.—This taxon shows somewhat more bluntly rounded apices and a less distinctly defined stauros than do the specimens illustrated by Hustedt (1959); otherwise, it appears to be similar to S. salina. Rare in the nonmarine assemblage. Known geologic range.—Not previously reported as a fossil, to the writers’ knowledge. S. salina is known from modern saline and brackish-water environments. REFERENCES CITED Abbott, W. H. 1978. Correlation and zonation of Miocene strata along the At- lantic margin of North America using diatoms and silico- flagellates. Marine Micropaleontology, vol. 3, pp. 15-34, DIS 162% 1980. Diatoms and stratigraphically significant silicoflagellates from the Atlantic Margin Coring Project and other Atlantic Margin sites. Micropaleontology, vol. 26, No. 1, pp. 49- 80, pls. 1-6. Abbott, W. H., and Andrews, G. W. 1979. Middle Miocene marine diatoms from the Hawthorn For- mation of the Ridgeland Trough, South Carolina and Georgia. 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Torrey Bot. Club, Bull., vol. 6, pp. 71-76, 207-210. Kanaya, T. 1959. Miocene diatom assemblages from the Onnagawa For- mation and their distribution in the correlative formations in northeast Japan. Tohoku Univ. Sci. Repts., ser. 2 (Geol), vol. 30, pp. 1-130. Kitton, F. 1870, 1871. Diatomaceous deposits from Jutland. Quekett Mi- crosc. Club, J., vol. 1, pp. 99-102, 1870; vol. 2, pp. 168- 171, 1871; Koizumi, I. 1973. The late Cenozoic diatoms of sites 183-193, leg 19, Deep Sea Drilling Project. Initial Reports of the Deep Sea Drill- ing Project, vol. 19, pp. 805-855. Kützing, F. T. 1844. Die kieselschaligen Bacillarien oder Diatomeen. Nordhau- sen, W. Kohne, pp. 1-152, pls. 1-30. 1849. Species algarum. Leipzig, F. A. Brockhaus, pp. 1-922. Laporte, L. J., and Lefebure, P. 1929. Diatomées rares et curieuses. Paris, privately printed, vol. 1, pls. 1-15. Lohman, K. E. 1938. Pliocene diatoms from the Kettleman Hills, California. U. S. Geol. Surv., Prof. Paper, 189-C, pp. 81-94, pls. 20- 23: 1941. Geology and biology of North Atlantic deep-sea cores be- tween Newfoundland and Ireland, Part 3, Diatomaceae. U. S. Geol. Surv., Prof. Paper 196(3): pp. 55-86, pls. 12- FR 94 BULLETIN 321 Lohman, K. E. 1948. Middle Miocene diatoms from the Hammond Well. In: Cretaceous and Tertiary subsurface geology. Maryland Dept. Geol., Mines, Water Resources, Bull. 2, pp. 151- 187, 331-333, pls. 5-11. 1974. Lower middle Miocene diatoms from Trinidad. Naturf. Ges. Basel Verhandl., 84, No. 1, pp. 326-360, pls. 1-6. Lohman, K. E., and Andrews, G. W. 1968. Late Eocene nonmarine diatoms from the Beaver Divide area, Fremont county, Wyoming. U. S. Geol. Surv., Prof. Paper 593-E, pp. El-E26, pls. 1, 2. Long, J. A., Fuge, D. P., and Smith, J. 1946. Diatoms of the Moreno Shale. J. Paleontology, vol. 20, pp. 89-118, pls. 13-19. Lyngbye, H. C. 1819. Tentamen Hydrophytologiae Danicae. Hafnia, pp. 1-248, pls. 1-70. Mann, A. 1924. The fossil swamp deposit at the Walker Hotel site, Con- necticut Avenue and DeSales Street, Washington, D.C. Diatom deposit found in the excavation. Washington Acad. Sci., J., vol., 14, No. 1, pp. 26-32, pl. 1. Moore, R. C. 1954. Kingdom of organisms named Protista. J. Paleontology, vol. 28, pp. 588-598. Müller, O. F. 1788. De Confervis palustribus oculo nudo invisibilis. Nova Acta Acad. Ser. Imp. Petropolitanae, vol. 3, p. 91, pl. 1. Pantocsek, J. 1886, 1889. Beiträge zur Kenntniss der fossilen Bacillarien Un- garns. Nagy-Tapolcsany, Julius Platzko: pt. 1, pp. 1-75, pls. 1-30, 1886; pt. 2, pp. 1-122, pls. 1-30, 1889. Patrick, R., and Reimer, C. W. 1966, 1975. The diatoms of the United States. Acad. Nat. Sci. Philadelphia, Mon. 13: vol. 1, pp. 1-688, 64 pls. 1966; vol. 2, pp. 1-213, 28 pls. 1975. Patterson, S. H. 1974. Fuller’s earth and other industrial mineral resources of the Meigs-Attapulgus-Quincy District, Georgia and Florida. U. S. Geol. Surv., Prof. Paper 828, pp. 1-45, pls. 1-2. Patterson, S. H., and Buie, B. F. 1974. Field conference on kaolin and fuller’s earth, November 14-16, 1974. Georgia Geol. Surv., Guideb. 14, pp. 1-53. Pritchard, A. 1861. Id Goscinodiscas perforatus var. cellulosus GINO Tr a a wesen een, 74 USGS Diatom Cat. no. 3965-2, x 1000, diameter 82 um. 19.2C0seinodiseussrothii. (Ehrenbers))GRUNoWERT ee ee ay en E eS aste EE 75 USGS Diatom Cat. no. 3953-1, x 1000, diameter 47 um. 98 Figure de 11-13. 21,22 28, 29. 30. 31.32 33: BULLETIN 321 EXPLANATION OF PLATE 8 Page GCosemodiweus Vor (ENTIDAD EE eris ee acere ee > USGS Diatom Cat. no. 3959-19, x 1000, diameter 57 um. - Cymatogonia amblyoceros (Ehrenberg) Hanna ee 15 2. USGS Diatom Cat. no. 3959-39, x 1000, height 42 um. 3. USGS Diatom Cat. no. 3963-33, x 1000, height 39 um. O A PMOL à 2 scx. EE 76 4. USGS Diatom Cat. no. 3969-28, x 1000, length 59 um. 5. USGS Diatom Cat. no. 3969-56, x 1000, length 70 um. E Catos a ammini OA Abbott... eu... e revues A A a 76 USGS Diatom Cat. no. 3969-9, x 1000, length 35 um. REC a tos tilo enana STUD ne BEER D QE uec eec eee Feed ere ee enden e 76 7. USGS Diatom Cat. no. 3989-17, x1000, length 20 um. 8. USGS Diatom Cat. no. 3990-18, x1000, length 18 um. L Deiphirkers unpustata F antoeselo) Andrewsi. PAL ER Dee He ss Wey Oe Rer meh RR Ea ee e gens seine e e S e e 77 9. USGS Diatom Cat. no. 3970-44, x 1000, length 52 um. 10. USGS Diatom Cat. no. 3963-37, x 1000, length 69 um. EE 77 11. USGS Diatom Cat. no. 3961-1, x 1000, length 35 um. 12. USGS Diatom Cat. no. 3969-89, x 1000, length 38 um. 13. USGS Diatom Cat. no. 3959-18, x 1000, length 44 um. . Delphineis novaecaesaraea (Kain and Schultze) Andrews ............................................................... Wil USGS Diatom Cat. no. 3961-32, x 1000, length of fragment 59 um. = Diploners crabro: (Ehrenbere) Blitenberg a EE EE bette de RENE OR CA TRE RARE eee 78 15. USGS Diatom Cat. no. 3989-19, x 1000, length 52 um. 16. USGS Diatom Cat. no. 3953-2, x 1000, length 43 um. ^ Diploneiv all D. suborbrenlaris (Gregory) Cleve-. cai eee o NS AM ARR RM AE Pr ARS RAA, RS 78 USGS Diatom Cat. no. 3969-47, x 1000, length 23 um. AA DN nn aie uM aS le USO. 78 USGS Diatom Cat. no. 3969-80, x 1000, width of fragment 31 um. GV OSTOING SINC CLES o a supe de ee ER URN coh vv ioa ENG WER EME NE SR SERIE AR RD UR a 79 USGS Diatom Cat. no. 3969-92, x 500, length of fragment 114 um. .. Grammutophoramarina (Lyngbye) ENEE 19 USGS Diatom Cat. no. 3961-9, x 1000, length 58 um. Hemiaulus bipons (Elmenbers) GrUBOW. sa... Ad wenn 79 21. USGS Diatom Cat. no. 3969-83, x 1000, length 32 um. 22. USGS Diatom Cat. no. 3959-20, x 1000, length 35 um. Hlyulddıseus SCOLICH EEN 79 USGS Diatom Cat. no. 3969-94, x 1000, diameter 49 um. INC A DUO EE E E E E EE 80 USGS Diatom Cat. no. 3961-29, x 1000, length 27 um. = Lithodesminne Ehrenbergin. (Snow) POLÍ EE 80 USGS Diatom Cat. no. 3953-36, x 1000, length 39 um. AO IA E aT e ee Na net O END Seu roter 80 USGS Diatom Cat. no. 3989-21, x 1000, length 39 um. ER DE EE A A E e et PIER hern 80 USGS Diatom Cat. no. 3969-58, x 1000, diameter 18 um. IE a A En N ERE EEEE ER 80 28. USGS Diatom Cat. no. 3969-27, x 1000, length 38 um. 29. USGS Diatom Cat. no. 3969-82, x 1000, length 67 um. Nabiont macular (Baley Edwards seee ee A O sey le Pe eH Favs Cen gts gt A NR eu UMS 81 USGS Diatom Cat. no. 3957-19, x 1000, length 48 um. IN ES CT SDS MIES NE ea Ls e EE EE, een: hens E E P 81 31. USGS Diatom Cat. no. 3963-7, x1000, length 53 um. 32. USGS Diatom Cat. no. 3970-17, x1000, length 62 um. Puane complert T Olay WS. +. an 109 Oa netu Ee sedere ccn mede e ee 81 USGS Diatom Cat. no. 3971-11, x1000, diameter 41 um. PLATE 8 Hitt ‚ur | BULLETINS OF AMERICAN PALEONTOLOGY, VOLUME 87 PLATE 9 BULLETINS OF AMERICAN PALEONTOLOGY, VOLUME 87 an sur DEA 795.0 00 0:08 000000 aa re © pa . à " P OOO M gie qat DXX 11-13. 14-16. 17-19. 20-22. 2/37 24. 25. 26. 216 28. 290 EIE 32 33, 34. DOE MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT EXPLANATION OF PLATE 9 < Paraliassuleatas(Ehrenberz)@leye cm. re ee nes ee USGS Diatom Cat. no. 3969-60, x 1000, diameter 27 um. JAeParaliassulcatasvar coronata (Bluenbers) Andrews ee... ee nen USGS Diatom Cat. no. 3989-23, x 1000, diameter 30 um. ‚Periptera petiolata Andrews e EU. EE RE E USGS Diatom Cat. no. 3969-72, x 1000, length 28 um. < Pleurosigmataite P. aestiarit (Bre biSsOm) SOLIDE ar Rs 4. USGS Diatom Cat. no. 3969-42, x 1000, length of fragment 44 um. 5. USGS Diatom Cat. no. 3970-10, x 1000, length 38 um. c Pyrgupyxisyolmnsonidndiklendey ex ape o ccce cl rM tuc o E nen. USGS Diatom Cat. no. 3970-38, x1000, length 66 um. . Rhaphoneis ad ter Andrews rn GL SS UIN Dc A UL. MM MEE JUNI V or n URP ie e E Me 7. USGS Diatom Cat. no. 3969-19, x1000, length 45 um. 8. USGS Diatom Cat. no. 3969-55, x1000, length 48 um. . Rhaphoneis elegans (Pantocsek and Grunow) Hanna... EENS erre 9. USGS Diatom Cat. no. 3963-7, x1000, length 35 um. 10. USGS Diatom Cat. no. 3967-27, x1000, length 36 um. Rhaphoneis fusıformiss Andrews c eee UU US E n ique SA ee... 11. USGS Diatom Cat. no. 3969-17, x1000, length 41 um. 12. USGS Diatom Cat. no. 3953-7, x1000, length 54 um. 13. USGS Diatom Cat. no. 3953-42, x1000, length 63 um. Rhaphoneis magnap VOIE AT REN Se CERE EA och Ret d oM cess ULM c SV MN EE 14. USGS Diatom Cat. no. 3965-29, x1000, length 130 um. 15. USGS Diatom Cat. no. 3959-40, x1000, length 104 um. 16. USGS Diatom Cat. no. 3953-38, x1000, length 75 um. Rhaphoneis- parks anha RR o LL o IE ec T toda e Ee CINE d 17. USGS Diatom Cat. no. 3990-31, x1000, length 33 um. 18. USGS Diatom Cat. no. 3953-17, x1000, length 49 um. 19. USGS Diatom Cat. no. 3953-18, x1000, length 72 um. Rossiella paleacea- (Grunow) Desikachary and Maheshwanle ccce c ccc M TUE E. 20. USGS Diatom Cat. no. 3963-17, x1000, length 29 um. 21. USGS Diatom Cat. no. 3970-7, x1000, length 39 um. 22. USGS Diatom Cat. no. 3970-1, x1000, length 44 um. Stephanopyxis turbis Gre ville) Rasse wenn T Ete ae eesti seris deu MEVS cL DECRE à USGS Diatom Cat. no. 3965-30, x1000, diameter 39 um. Thalassionemma nitzschioidesGirunow) EE USGS Diatom Cat. no. 3959-10, x1000, length 75 um. Thalassionemarobtusum(@ininow) Andrews me ee... usc Ic ee USGS Diatom Cat. no. 3969-45, x 1000, length 48 um. Mhalssiothrisslongissima.@leve and @mnowe man. Kr Mu Mom cH e USGS Diatom Cat. no. 3990-35, x1000, length of fragment 61 um. SCOS OM AU OEN ÍA t a CAL ERE UN per le mM eU KK. en moa E... USGS Diatom Cat. no. 3959-22, x1000, diameter 59 um. Thalassiosirakeccentrica(ENTenberp)I@leyer mn u AR e cud ICD EA IM e USGS Diatom Cat. no. 3953-5, x1000, diameter 37 um. ThalussiosiraMeptopus (Gun on) ASC an Xe leet ue... ct uu Nucl uu c I e EE E 29. USGS Diatom Cat. no. 3961-25, x1000, diameter 25 um. 30. USGS Diatom Cat. no. 3953-41, x1000, diameter 34 um. Thalassiosira SPECS A ee I So RR SR Ro LC c M M E TU LII e USGS Diatom Cat. no. 3961-11, x1000, diameter 25 um. SEH USGS Diatom Cat. no. 3990-36, x 1000, height 33 um. EE EE pear ree ann oe os aA gehen. 33. Girdle view, USGS Diatom Cat. no. 3969-78, x 1000, width 35 um. 34. Valve view, USGS Diatom Cat. no. 3970-15, x 1000, height 26 um. Genus HEET EE Grs alas ei onl UM E uaa. weal, a cba cos a USGS Diatom Cat. no. 3963-24, x 1000, length 57 um. 99 100 BULLETIN 321 EXPLANATION OF PLATE 10 Figure Page T- Achnanthes hungarica (Grunow) OLBUOW 25090: Me en o cin à IEEE ERU NN a 88 USGS Diatom Cat. no. 4165-3, x 1000, length 18 um. 2 E O e en le ed oo n etri eene ON a RR 88 USGS Diatom Cat. no. 4165-15, x 500, length 108 um. S. Eunoria peeimals (Müller) Rabenhorst.. 2... me... aan EN De UNE A. sis de E 88 USGS Diatom Cat. no. 4165-2, x 1000, length of fragment 37 um. 4. Eunotia pectinalis var: minor (Kützing) Rabenhorst .........2...sun nn Sees en nn EE NN nude. 88 USGS Diatom Cat. no. 4165-8, x 1000, length 37 um. 5. Gomphonema- affine Var insigne (Gregory) Andrews ran... o Eee 89 USGS Diatom Cat. no. 4165-13, x 1000, length 54 um. 6. Gyrosigma att. 6. spenceru (Quekett) Grifithrand Henfrey «oo. ns ee en 89 USGS Diatom Cat. no. 4165-24, x 500, length about 100 um. TEMPLOS TO ED LE E 89 USGS Diatom Cat. no. 4165-14, x 500, diameter 20 um. SENDICHIRANEN. radiosa 019 00 EE EE dt ee v LP le us 89 USGS Diatom Cat. no. 4165-19, x 1000, length 58 um. 9. Nüzsehta BV IAG OW e à OR ole Meas RR ee a eve gas NN CO CR A A 90 USGS Diatom Cat. no. 4165-5, x 1000, length of fragment 52 um. 10. Nitzschia tryblionella var. victoriae (Grunow) Crunow. EE 90 USGS Diatom Cat. no. 4165-22, x1000, length 55 um. ED. SPP TAVITA breytcostat leve EEE aer ceci dom de on ciae D At aL d Lens HUN re cH e APAE E tL Ee, Ze 90 USGS Diatom Cat. no. 4165-12, x1000, length 63 um. 19S COPI West (Stt BELGIO. cris ce E Emudesc Nc Nue T. qe MCI Ad 88 USGS Diatom Cat. no. 4165-4, x1000, length 60 um. ES Pag O AMS A a St eM E 6 ce cer erbe ee Rod LAURE ER Nad LOR 90 USGS Diatom Cat. no. 4165-18, x 500, length 104 um. ta Pine a O DOUdCRE EOS s eo oem ess eeu cer E A ceti Some uma metum 90 USGS Diatom Cat. no. 4165-9, x 500, length 156 um. 15% PHOTOS all P PHOTDSIOU TOR (ERICBDCOUS)Cleve.. so i da aa e e en C ra SRI ueteres ans ae 90 USGS Diatom Cat. no. 4165-7, x1000, length of fragment 39 um. LG SIuroners A Sit oS MR Ces nre ee Et eR eres E O 91 USGS Diatom Cat. no. 4165-17, x1000, length 41 um. RA 18: Mormoptyehus aequalis Andrews, DEW SPOOLS ais «uer oh s e ME dl pon HART RENE 69 17. Exterior of 14-sectored specimen, USGS diatom locality 6469, x 750, diameter 88 um. 18. Exterior of deeply crenulate 12-sectored specimen, x1500, diameter 47 um. Scanning electron micrographs. PLATE 10 BULLETINS OF AMERICAN PALEONTOLOGY, VOLUME 87 Een, BULLETINS OF AMERICAN PALEONTOLOGY, VOLUME 87 PLATE 11 MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 101 EXPLANATION OF PLATE 11 Scanning electron micrographs Figure Page l=6. Actinoptychus degudas ‘Andrews; new Speciosa ete EE 69 1. Girdle view of frustule, 12-sectored specimen, USGS diatom locality 6469, x 1500, diameter 49 um. 2. Interior of 12-sectored specimen, USGS diatom locality 6469, x 1700, diameter 41 um. . Detail of edge of valve shown in figure 1, x 5250. . Detail of labiate process in specimen shown in figure 2, x 27,500. . Detail of inside of valve and aberrant labiate process, USGS diatom locality 6469, x 10,000. . Detail of pore structure on interior of valve, same specimen as figure 5, x 15,000. SU RU 102 BULLETIN 321 EXPLANATION OF PLATE 12 Scanning electron micrographs Figure Page le vAUCHHODty elus senarius (Ebveubergycbhrenbertgo et EE nals MEC OC mean et a mt Dan GAR SAD ce 70 1. Interior of valve showing three labiate processes in each raised sector. USGS diatom locality 5578, x 2500, diameter 32 um. 2. Interior of valve showing three labiate processes in each raised sector and one off-center labiate process in each depressed sector. USGS diatom locality 5578, x 2000, diameter 36 um. AA A A ee dE d COP ENTIER a gta SC ei 76 Exterior of valve, USGS diatom locality 5578, x 2000, diameter 36 um. 4 e Bailey: a uou eer rto OR eee EE IE QE UR ne ne UD C REN SR a 87 Girdle view of valve with attached girdle bands, USGS diatom locality 5578, x1200, diameter 56 um. PLATE 12 EN BULLETINS OF AMERICAN PALEONTOLOGY, VOLUME 87 PLATE 13 MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 103 EXPLANATION OF PLATE 13 Scanning electron micrographs Figure Page Eeer T7 Exterior of valve, USGS diatom locality 5578, x 3500, length 24 um. 2, 3. Rhaphoneis ad LEAD ARSS Ta E RIEN ne ER doses c e LES ES CR 82 2. Interior of valve, USGS diatom locality 5578, x 1600, length 44 um. 3. Detail of interior of another specimen, same locality, showing labiate process and sieve plates, x 8900. -Rhaphoneis elegans (Pantocsek and: Grunow Hannas weer ies. a TOT yah 83 Exterior of valve, USGS diatom locality 6468, x 2000, length 38 um. V Rhdphoneis fusiformis: ANTON SS RR HO Rte re AAA vetns 83 Interior of valve, USGS diatom locality 5578, x 2400, length 46 um. c Rhaphoneis PATS ANA mt. MN OT P So or OI D N EE 83 Interior of valve, USGS diatom locality 5578, x 1500, length about 70 um. 2 RhHaüphoneis magnapuncidra AN ATEN S: ANNE RENAN TE E A l'on oa 83 Interior of valve, USGS diatom locality 5578, x 1200, length about 78 um. 104 BULLETIN 321 INDEX Note: Page numbers are in light face, plate numbers are in bold face type; numbers in italics indicate principal discussions. Abbott (1978) Abbott (1980) Abbott (1983) Abbott and Andrews (1979) ................... 62,63,68,70-82,84-87 Abbott and Binddlestim (1980) 2... ee. nn en 57 Achnanthes hungarica (Grunow) Grunow, 1880 .... 10 ...... 62,88 Achnanthidium hungaricum Grunow, 1863 ......................... 88 Actinocyclus Ehrenberg, 1838 ; COPE Eno AUS 10 en... ee ET eco ces 68 ehrenbergii var. tenella (Brébisson) Hustedt, 1929 ............. 68 ingens Rattray, 1890 ......... normanii Hustedt, 1957a ... EE EE, ss cede Rs eher DELONAS Ehrenberg, 1838 cotarro comen emeret oe senarius Ehrenberg, 1838 ......... tenellus (Brebisson) Andrews .... Actinoptychus Ehrenberg, 1841 aequalis Andrews, n. sp. ...... 6,10,11 ...... 57,60,62,64,69-70 amblyoceros (Ehrenberg) Schmidt, 1874 ........................... 2 heliopelta Grunow, 1883 70 TOLDO OGU AMOLES, FITO eu cream Oran 62,70 senarius (Ehrenberg) Ehrenberg, 1843 ..... 612 rear 69,70,76 OA var: Tommi CHAN I9 80:3. Leer eere eee eto Rea a ia erre iun (Schmidt) Hanna, 1932 ran. san undulatus (Bailey) Ralfs, 1861 ............. virginicus (Grunow) Andrews, 1976 vulgaris var. virginica Grunow, 1883 QUOC, RUGDNONCIS eoe eere eri ed aequalis, Actinoptychus ........... 6,10,11 E nn derriere dec ee gestuar (ali); Pleurosiemnesss. seen D 82 affine var. insigne, Gomphonema ................. TOS os 62,63,89 AAI 1190: v EL eege 16 E ERAT vie 89 a MENS ee 57 alata, Navicula 71 ADS AR RE AI sen O 71 Ahoa BTS VADE ee EE 5 GIRDISUNS, EE 63,79 amblyoceros, ACTIVO CITAS EE Edu berne eere rr ceso CERES le ie 75 ETAT ORONO a UN ee SEA 75, DICO DEV O nene A crée ce ie ee 15 Amphiprora aff. A. alata (Ehrenberg) Kützing, 1844 .. 6 ...... ZEN Anaulus birostratus (Grunow) Grunow, 1882 ................... 935/21 OOV CLONE CURE NE A 63,64,72,88-91 AOTC we Cho TM o ramos dde coiso vs aro mei EE, 63,64,72,89,90 Andre OT Re drame busses ree Tes EROR 67 Andrews (1975) ... 76,77,83 Andrews (1976) ... 68,70,72-75,77,79-82,84-87 Pavo: (19/0575 Ter Muerte owas avec ee A E 4/41 Andrews (1978) 62,63,70,71,77,78,82,83 Ponts) Gores CS A LI D TET 70 Pone O) eite ee NS 71-73,79-82,85,86 angustata, DCW HITIOIS E constat EEN 8. 62,77 PRA 01010) ia ER ea accra UR cs Gace EE TI Appalachian Monnan nee me 65 Appalachicola Embayment arenaria, Nayioula EES argus, AA CO CUS ER TR ea LI gi esee Tl SIRF LD OCIS CUS Cee va sais «id. Ta Rte E pal EE E Ser Re core ES 89 Ee Eeer TEE 63,73 Atlantic Ocean. ste less, 58,64,65 Aulacodiscus argus (Ehrenberg) Schmidt, 1886 ......... VEM Val Aulacosira italica (Ehrenberg) Simonsen, 1979 ..... (RES 64,72 Auliscus Ehrenberg, 1843 COCIAIUS Bailey, LS SA ne nn nr E a 42 SCUIDIUS (Smith) RAS lis GU pro 995 7 9 "BO 72. amua, IQ AULD NIG ee ee, DEE 72 CUNAS: DIO NA ON en RENE ten 12 Bailey (1844) Bailey (1845) Bailey (1850) Barrons) A N are 58 Batrom ISO a ee E 68 belgica, EE BA 76 BETHEL 64 Biddulphia Gray, 1821 aurita (Lyngbye) Brébisson, 19909 99. 2. TRE tee 72 Dirostrar d Imon EEN 71 tuomeyi (Bailey) Roper, 1859 ......................... zu 64,72 Diharensiss Gymatosira; Sete. Ste Sea. NE. 76 UlpoldrissLiradiscust VEN ATT aed RIV ee ee Sema. 80 bipons, AAA a ARE ea dt ZLVLOCCION E EE birostrata, Biddulphia ... birostratus, Anaulus ...... EE o dn Blow: CUS GQ) ME LL CR C Bogorovia paleaceus (Rattray) Jousé, 1976 ........................... bombus DONAS EU ee Bradbury o EE BTÉDISSO SSD) nier nn Ser Bréissel ee EE E brevicostdio EnaA EE ee EE ER, Bine, EE 58 CaelatUS AM CUS e EE EE EE 72 Caloneis Cleve, 1894 ELE 88 westii (Smith) Hendey, 1964 ..................... T0555 62,65,88 Calvert EoOumallon 08e. nr 57,63,71,74—77,80,83,85 “Chattahoochee emDayment soe dT I, 57 Choptank Formation ........: oU RR E 63,68,71,77,85 Cleve (1873) 81,86 Cleve CUS OD ie Son NE en dires anne tee TE 90 GIG VE (592) Eve o asian EE eg, 78,88,89 (len Ee Ee 90 Cleve CUO a nee RA 86 Cleve amd OPINO WAS SO) aa usares acres A E S 86 complexa, Melot an nr ete OE eet SRT 81 BE 81 9 87 MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 105 Gönferyaspeennals Müller, 1788 Hot 88 Diploneis Ehrenberg, 1840 Eoosawhatlchieequiyalent beds e eese IRE 57,59,62-64 bombuss(Ebnenberg)i@leves1s94. ner. e 63,78 GONNA EE 58 crabro (Ehrenberg) Ehrenberg, 1854 ..................... SES 78 corona, aff. D. orbicularis (Gregory) Cleve, 18904... 78 SICON OD IS. sro EE 63,84 DORE CLS ÉD) o REA ee 80 SA IM SA AN E E E A A 84 eelste E eee a OS 82 A nn E ON Coscinodiscus Ehrenberg, 1838 CGCENINICA) EE asteromphalus Ehrenberg, 1844 eccentricus, Coscinodiscus ... curvatulus Grunow, 1878 ........... Edwards (1860) una. decrescens Grunow, EE Ehrenberg (1838) .............. se See diorama Schmidt, 1878... O die ee eccentricus Ehrenberg, 1841 un ROL 71,74,80,86 elegans Greville, 1866 Ehrenberg (1843) ... s 69,74,88,90 excentricus Ehrenberg gigas var. diorama (Schmidt) Grunow, 1884 ................. 63,73 lacustris Grunow, 1880 73 leptopus Grunow, 1889 86 lineatus Ehrenberg AE cea GAG 86 (lineatus var.?) leptopus Grunow, 1883 ..…........................... 86 marginatus Ehrenberg, 1843 HUASCO Ee PAR essere aaa oculus-iridis Ehrenberg, 1841 .. Daleaceuss (Guunow Rattray, LRO eee DerforatusabhrenDerpededde «sca 1 ees perforatus var. cellulosus Grunow, 1884 praepaleaceus Schrader, 1973a .................. rothii (Ehrenberg) Grunow, 1878 .... SCH EE VELUSTISST MUS BANTO SOR; Re ne crabro, Diploneis Creswellia turris Greville, 1857 cruciata, Pyxidicula 85 curvatulus, Coscinodiscus 73 Cussia Schrader, 1974 paleacea (Grunow) Schrader, 1974 a ................................. 84 praepaleacea (Schrader) Schrader, 1974a .......................... 84 Gyclotella:seolioaiKutzingwlioddee te em 79 Cymatogonia amblyoceros (Ehrenberg) Ma EE B x 7 Cymatosira Grunow, 1862 belgica.GrıUnow, d SU Aer eens T Santee 76 DiNGGENSISMPANTOGSE Pe anr oe ES 76 immunis (Lohman) Abbott, 1979 nennen Suse 76 UNA ow SOR NU E TO 8 cu 76 IEN E ER el 5 Debya insignis Pantocsek, 1886 12255: 63,76 AETERNI COSCHOAISCHN UE de D RES 63175 Delphineis Andrews, 1977 angustata (Pantocsek) Andrews, 1977 .............. Bares 62,77 novaecaesaraea (Kain and Schultze) Andrews IT LEG an SEHR: 62,77 penelliptica Andrews, 1977 ...................- 8,13 Denmark, MOL Re RE Denteula Ntcobarica Grunów, 1870 M c TO ES Denticulopsis nicobarica (Grunow) Simonsen, 1979 ........ Desikachary and Maheshwari (1958) nt. DIO MACU Eyngbye, eos RR NS E A Er ae ee Dimeregramma novaecaesaraea Kain and Schultze, 1889 ...... TH dorama COSCINOUISCUS ROO e RERO en NI 3/5) Ehrenberg (1844) Ehrenberg (18452) Ehrenberg (1845b) Ehrenberg (1845c) Ehrenberg (1854) ehrenbergii, PACU MOG) CLUS EMER eG E eA ee E Ea e DES 68 PR OUEST crt RS EE NU 80 ehren berau var. tenella, Actinoeyehs ca sm ienen 68 elegans, COSO US tometer en 68 e, DIS ca 62,63,83 Endictya oceanica Ehrenberg, 1845b ....................... NL LU. 78 Eer) laueren 63,65 EE 10 7. 62,88 pectinalis (Müller) Rabenhorst, 1864 ............. T0 \ 62,88 pectinalis var. minor (Kützing) Rabenhorst ..... 1 2% 62,88 Eupodiscus Ehrenberg, 1844 sculptus Smith, 1853 ......... tenellus Brébisson, 1854 excentricus, Coscinodiscus ld AA ae EL e ademas to la formosa, OGL OCI ME e ct ANR ee et NAYARIT LEE Bag (ONE) ira da m M C O LU M ta RT A PAA vaL dia Fryxell and Hasle (1972) .......... PUGES GANT Rees ee SE e E Gaillonella Bory, 1825 coronata Ehronberg, IBASE id E 82 GE EE E Fe 72 StleatasEhrenberemlsssr mean Es 81 REM INU CNA RNAPNONCIS a ott O, DN 63 gemimijferäsyarselesans»Rhaphoneis.... ann 83 EE IE, ion me 57,60,63 CMG a a. Nations ras 37 Ro XD S COUV nina annee LOI re 37 BISASEVARSULOTAMASCOSEINORISCUS. un... en ann 63,73 Combos a A na pe. Rocco tit v le 78 Gomphonema Agardh, 1824 affine var. insigne (Gregory) ANGIEWS dO Umea IL eL UE eu 10 106 BULLETIN 321 Gomphonema Agardh, 1824 10e GREY 18368 u. BOR don eed eye es 89 lanceolatum var. insignis (Gregory) Cleve, 1894 ................ 89 Grammatophora marina (Lyngbye) Kützing, 1844 ................ 79 grandis, Sceptroneis : TAR E FMI e S dep pe ee unsre dao EE EE EE EECH (Ee e EE LEE EE 58 (A O e Sens Re E t M c RI 60 Greville (1857) 85 Greville (1861) 85 Greville (1863) 12 Greville (1865) 82 Greville (1866) 68 SEAN And EDITÉ EE 89 Guo AS PURO A 5.5 eror deser nee nen avers 82 Go EC OCT) EE RER ne 76,86,90 E inc nine a nord ie rie 71,88 AO) TARN O INT FEAL Grunow (1878) e [Gp dano CLS iad nas nest Foc av cents AO 79 CON COO UIS. eon cence ela les tigris rer EE 73,88-90 (EATEN Na RUE A) adde a M UE T T US RE 76,77,86 SHON WLS ee PR E 72,79,84,87 (AA Rt, E A Se m e etre 80,84,86 CO NES E desk or nr nique 73,74,79 CE OME RECON ee ecrire mr EE 58,62 Cub Siro ee ies ae reapers naps ee 57,58,64 Geb HE ET e le eee 58 Gyrosigma Hassall, 1845 aff. G. spencerii (Quekett) Gibt and Hienirey, 18962... dO: cs 62,65,89 DCN A a O UE O 79 a Ea MA MR een RR A thane 66 A no crian E MC E ci 68 AN COD et RER AE reser ewe eae TUE e 66 rire bou Md ed Me RR A TET. 70,75,76,83,85 TESTE AREA Renee T M M 2 75 FAAS CHIT E A des cie 86 ora Dede. es uen oc ee 57 Hawthorn Formation, Coosawhatchie Clay Member ...... 57,60,63,68,70,75-78,80-86 EECH 57 O e NO ne ee py heiiopein, EE atu e g s E e 70 Hemiaulus Ehrenberg, 1844 ambiguus RUMO NGS TE PARUS es ecc ewe taii ne 63,79 bipons (Ehrenberg) Grunow, 1882 TE 79 polyrmorphus GION, 1884... e bt dco enger an, 63,79 Hendey (L964) -erreen eerie ezeren 65,66,71—76,78—82,84—88 EC Eeer 82 HendıysandsSproul(1906) u... nenn aa. eu 58 Hetrick Ata Vorms QUIDS) ner em PUR e Cc 58 Himatidium minus Kützing, 1844 ...................................... 88 Eval Wate IbXOISSION ne tamale ene) 89 Huddlestun (1981) 57 VURCANICH EE d'Us 62,88 hungaricum, Achnanthidium .......................................... 88 IIA E T DU E Wl Hostet 1927-1959)... REN AREN ne 65,66 EINSTEIN. een EEN 72,80,89 IA ee 73-75,78,79,81,82,85,86 A 0). e ee FREENET: 71,72,84,86 Elustecit (1930) areas nee 71,72,79,80,87 Hustedt (1930a) Hustedt (1931) Hustedt (1932) Hustedt (1933) Hustedt (1937) Hustedt (1957a) Hustedt (1959) Hustedt (1966) Hyalodiscus scoticus (Kützing) Grunow, 1845b .... 8 ...... 64,79 TONI ANTRO Se ee N 10323: % 62,65, 90 TITUS RT ee eee Unter USER 76 LIER OL aN ILZSCH Cec. BEREITEN ROUTE RES VISOS, SE 81 EE RO 63,68 EE 89 LISTS HIS ADO D) Ce ea E AE Re 125. v 63,76 EE 87 italica, PAIL GO SENG a E Rene ee TRUE DI tee Ma Gs 64,72 ECE OT oet iria aaa e M ER IE der CDR 72 AUF IATER EE AR en 72 Johnson: (892) ra Eh ERC 58 Johnsoniana, JE ROT eS e ODF 82 EE RIT BI M 82 TOUS en A OR HARE 84 NOVA IAS Mera pol ESSE En ect E 63,85 EE EE 101.78 62,65,89 Kain.and«Schültze. (1889), er atl ee RM 3j EE EE 00 Klo SEE ee EEE ee 87 ¡MOMIAS TICLOAISOUS Term RARO (ARE 85 orrainn IAS) rene dE ENEE ER 85 ere 71,72,79,81,88,89 LACUS TV ISH GOSODTOQISQUSS ee Re ST Kë lanceolatum var. insignis, Gomphonema irar Fa 89 ALEA TALC. en ne TL A ANLE 64 Laporte ana kele bure (L929)... UE ask ieee ANT TIR 82 leptopus, (a LIS CUSTOM RR I 86 RALES OS INCL Rates ext Battin ni ete ER e 9 86 lineata, ISTODHONODY Need EE 63,85 DEER ER lineatus, (GOSCINOGISCUS Er 86 Stephanodiscus 85 (lineatus ar) [EDIOp Us aC OSCINOAISCUS en ee TER NN 86 Liradiscus bipolaris Lohman, 1948 ......................... Sit tes 80 Lithodesmium Ehrenberg, 1840 ehrenbergii (Grunow) Forti, 1912 ........................ Sen. 80 undulatum Ehrenberg, 1841 ............................... si 80 br EE een DEE ORTU E u) Porman (do 4D) 06 Re. 73,75,81,86 Lohman (TIAS) uere rire tanins 71-77,79-81,83,85-87 BOAT OSAN R E E ee 77,19,83 Lohman and Andrews (1968) Bi Aue tees 66,72 Long. ice arca Smith (LIAO) no or no oa RR 66 MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 107 longissima, Thalassiothrix Be ein 86 NOWE ELA Cat re 85 lorenziana, Cymatosira ........... es Se 76 novaecaesaraea, SNL IE GRO RE ER tts 122719 UDUIDHYHUISE eor iden eee 8: cs 62,77 VAS IAE eec te tti C EE T M. EG maculata, Navicula ...... obtusum Thalassionema ee ls gear 85,86 Stauroneis Ocala High Pr SEE WEEN 65 magnapunctata, Rhaphoneis ................. IS 62,63,83,88 GE e Sr 78 major var. asymmetrica (aff), Pinnularia ..….......................... 90 EE LB 68 MAN COD Aes TER een KEE 74 marginatus, Coscinodiscus orbieularıs (ALL) SD IDIOTICIS tae ihe RE LM 78 marina, Grammatophora Mi ba E paleacea, Chesapeake Bay Region Cussia EA Hee elle DE 62,70 Rossiella Melosira Agardh, 1824 Stoschia complexa Lohman, OA Ge er Bus 81 paleaceus, italica (Ehrenberg) Kützinge, 1844 Re 712) Bogorovia UNE elle LO. 62,65,89 Coscinodiscus (Paralia) sulcata var. coronata (Ehrenberg) Grunow, 1882 .. 82 AS ee EN sülcata (Ehrenberg) Kützine, laden ne BE dE Ee sulcata forma coronata Hustedt, 1928 West Smile acid IMICTOSTA UNO NOS TAURO DLC a Atas a ere ee microstauron (aff), Pinnularia .... PUNUS UPA ee Monroe Greeks Sang Stole EE Moore (1954) Müller (1788) Navicula Bory, 1822 GESTUATITEBHEDISSON AS AO Ne en RAM teen alata Ehrenberg, 1840 ............... arenaria Donkin, 1861 .............. OF MOSGIGTER OLY MSS CDR na SU LOSS maculata (Bailey) Edwards, 1860 aff. N. radiosa Kützing, 1844 ............... smithii var. suborbicularis Gregory, 1857 ........................…. 78 ET 89 TOMANDO EE 90 WAOSDIESTIIHKE Ee URS 88 EE STEEN Pine Ridge area New Zealand, OAIUADUN Re ee ee 82 nicobarica, IL Ee TT. dee 63,77 nitidus, EE EE 74 ESOT Ee Eer 74 Nitzschia Hassall, 1845 AVONA Gino USO eer tee T 1027. 62,65,90 LIND CV {OVATAPANOLEWSt ISO te not es 81 tryblionella var. victoriae (Grunow) GTO MG ISSO! EE arts. DO 62,65,90 SPECIES RAS m N N Tne SX 81 nitzschioides, ISOC NUMMER CV feels mse ERO ROT T 86 VEAS AA RR RE S Que 86 nitzschioides var. obtusa, Thalassiothrix 86 TORT SACO VOUS eU CE ea SEE en RR ILS) EE EE "S Pantocsek and Grunow (1886) Paralia Heiberg, 1863 complexa (Lohman) Andrews, 1976 oo... See 81 sulcata (Ehrenberg) Cleve, 1873 ............. N aeh 60,64,81,87 sulcata var. coronata (Ehrenberg) IV A en ge 60,64,81,82 paralela EE WHO CUN NES RE ER 102.0 62,88 Dans Rap NES EEE ee een ga 62,63,83 Rate and RENTE CG) EE UU UN 88-90 Paic kand Renner (975) ccs A Oe 89 BEL ee o ES I ES ea nt eas Patterson IIA Patterson and Buie (1974) pectinalis, COINTE EE ra EE 88 VA RE D Ie et ee EAS 62,88 Deetinalıssyanı minor UNONA NN en 107577 62,88 e Ee 62,63,77 DER ONAUUS AGO SCD EE ren 74 perforatus var. cellulosus, Coscinodiscus .................. ER 74 Periptera petiolata Andrews, 1979 ........................ gru: 82 Peristephania lineata Ehrenberg, 1854 ............................... 85 Pelo atum OPIDO dest ee e iie TIT ga 82 Pinnularia Ehrenberg, 1843 brevicostata@leve, 189] a T0 62,63,90 (Diploneis) bombus Ehrenberg, 184441 00 78 (Diploneis)\icrabro Bhrenberg, T844 el 78 Jus anar Andres LITI cui c c 10.25: 62,63,90 aff. P. major var. asymmetrica Cleve, 1895 ...................... 90 aff. P. microstauron (Ehrenberg) (loy EN Se Se re 10 62,63,90 torna Manny Patrick DOOR TU 90 Pleurosigma aff. P. aestuarii (Brébisson) SIDE ALSO SS ee Je 82 DOW MOND NUS CM Ulsa MS 63,79 praepaleacea, (ERS orem a A en iode ce M TM ROSSI NR EET, praepaleaceus, Coscinodiscus Psammodiscus nitidus (Gregory) Round and Mann, 1980 ...... 74 BULBO ARI SEO ALO Se ema ien RAIN ANI AS 84 PürirandaVernonid9604) ec Ee 37 Pyrgupyxis johnsoniana Hendey, 1969 .................... VI orc 82 108 BULLETIN 321 yx a.cruciata Ehrenberg, 164320 rer 85 Pyxilla johnsoniana Grove and Sturt, 1887 ......................... 82 net Cb ntis N MAS. eas 89 RADEON OOM) een ee ae 88 radiosa (afk), Navicula ................. Ge | Vee eer RAS CSG DR ice Rattray (1888a) e RENIN s EE TOT na na Renee 12 In SEE TL E 72,84,86 NEA do uror ER Re master ates 68 Rhaphoneis Ehrenberg, 1844 ; adamantea Andrews, 1978 .......... ees OS os 62,63,82 EEN REESEN p elegans (Pantocsek and Grunow) Bel 013. 62,63,83 Jusiformis Andrews; 1978 .................... 913 o. 62,63,83 LenmmnyerdEhrenbere 1844. 41... ho nao RR 63 gemmifera var. elegans Pantocsek and Grunow, 1886 ........ 83 magnapunctata Andrews, 1978 .......... 913 us: 62,63,83,88 Dons Elena, E 9,13; nam 62,63,83 Rhizosolenia styliformis Brightwell, 1858 ........................ 63,84 LA Biouish scoot oy Cro EE 63 [ECOL EI oer ite own nas e ETE speciali nefas eius A N 75 ee ME Om D, Rossiella Desikachary and Maheshwari, 1958 paleacea (Grunow) Desikachary and MARIS DAD IUS aan ES LEE 84 praepaleacea (Schrader) Andrews, new combination ...... 63,84 VOUIT, EE digas de 15 sana (atas PAU ON atia. uere cera eoo erano cavado 10/5. 65,91 Scentroneis grandis Abbott; 1983 vacio amt erede ever pres 63,84 imm 1 ds CN decime ee MU RSC MT TR er UE 1/5) Schmidt (1878) 73 Schmidt (1882) 85 Schmidt (1885) 87 Schardt CE GOO) ER ae T E c recone 70,71 EIERE 77,84,85,87 MOLT O (SD) SAR A Re a ege T: EE ee eames 84 Sobrado and e nee 76,85 CODE ELO) DID PAR Reiser ced ree tie pa db pd ere ceo 79 SCONCUS AY O DISCUSS E CIL mer 64,79 sculptus, APIS Sea EE REEL EUMD cus ci e ala tie amet Aug eere ce y i fer 72 ONDOUI EA E E nee nee ake 12 senarius, SEHE AAL ces RITENA EE 70 CLIO A ee ee OET 017... 69,70,76 ee A nere ee 64 Sheshukova-Poretskaya (1962)... 322 er drogue e 85 SheshukovasBoreiskaya (196/72). ren. eive nenne 87 Sion DID a cot aa 67,72,77 tonta eins ad kanaya (1961) u... sr 77 Corn eon) oM N EM 72,82,88,91 Sonde NEC MEE EET UNT 80 smithii var. suborbicularis, Navicula 78 NODI a lic a ies oso avec ries nement y 57,60,63 Getters deele eege 57,58 spencerii, Navicula spencerii (aff.), Gyrosigma spinosa, Trochosira SDINOSUNDBLNICELANUM Sem re ae RD 87 Stauroneis Ehrenberg, 1843 maculna Bay US) en ee 81 All Ny QUESTI EOS een 107. 65,91 Stauroptera microstauron Ehrenberg, 1843 .......................... 90 Nela an ELIT EE 70 stellaris, Coscinodiscus Stephanodiscus lineatus Ehrenberg, 1854:......................... 85 Stephanopyxis Ehrenberg, 1844 corona (Ehrenberg) Grunow, 1882 lineata (Ehrenberg) Forti, 1912 .... turris (Greville) Ralfs, 1861 .............. d " Stierodiscus Kittonianus Greville, 1861. e 0 7 A te dav rte Wine plas E Tm 58,60 S/OSGITO paleacea MEUM OWS EE 84 SUV IMOLINIS AR IZOSOICHIO® ven E 63,84 sulcata, AA Orn NN he C E oc RD ee 81 MELO AR Rare ne enr cove nating ance GoM ORL RR à Cas dice 81 TAN PRE o TE Ee Gr 60,64,81,87 sulcata torma coronata, Melositase ee 82 sukad var. coronata, E mereri ire o 60,64,81,82 Synedra Ehrenberg, 1832 jouseana Sheshukova-Poretskaya, 1962 ........................ 63,85 EREECHEN 86 AMES TUX CIN SS CA le Cac een acme Suite 86 Svsvepnania corona Ehrenberg, 1845a mese varus 84 tenellus, AAA ey A P DRC EE Oe NOSA a 68 EE 68 Thalassionema Grunow, 1881 nitzschioides (Grunow) Hustedt, 1932 .................. Sex e 86 obtusum (Grunow) Andrews, 1976 .................. Dee 85,86 Thalassiosira Cleve, 1873 eccentrica (Ehrenberg) Cleve, 1904 ...................... Des 86 leptopus (Grunow) Hasle and Fryxell, 1977 .......... er 86 SIS CLES AN ea en We ante WIA nn den ve Gare, 86 Thalassiothrix Cleve and Grunow, 1880 longissima Cleve and Grunow, 1880 ................... Je 86 NilZSCHICIAeS Val, ODIUSA GIUNOW, 1881... es 86 VICIOS STO IS NCAA a ere one e TQ EE 86 DREI cA CIITLO DEV CHUS rated tet eee in tin 62,63,70 torta, NAME ORDRE ARRET Ee er A 90 TAWA UCI Mae Petre ON E ee a Fete eee Ae men 90 LI a er EE 58 Triceratium Ehrenberg, 1841 EE Ee US GOdecoVnnmoibrenberp 139498 rn... 9 9 oye Ji 87 IMLCHDUNCTALUTIUGIEUNOWs 992 en erinan ae 87 DIOS UMD ALE SAO e cp Si 5 87 TEIDOGISGHS AES S Ehrenborg, Todal t0 ar TES ne e qi UFO HOSTS DINOS Klon S SUA NU ETT nn ae 63,87 TUE ee fe BEE 90 tryblionella var. victoriae, Nitzschia .............. 10,208 62,65,90 tuomeyi, VAN A une ecco aor T CIE: yim 64,72 SOC Roky DNUS DC am EM 72 turris, Ta aaa CEREREM M TERN ET 85 TODOS t ecu da E e REL aan 85 EUA EUA ole IA RTT 824 80 MIOCENE DIATOMS FROM GEORGIA: ANDREWS AND ABBOTT 109 UE 70 EE 58,60,63 USNM (U.S. National Museum of Natural History, Weaver and Beck (IN) a ee 58-60,65 Smithsonian Institution, Washington, DC) ................ 69,70 westii, (Garne ee TON cm 62,65,88 Valentine Romana leo 63,64,91 NAE ee ee Sara 60,64,80 Van AEUR EGE aE a A I EE al EE 88 Van Heurck (1883) vetustissimus, Coscinodiscus A A N ee IM 87 NIE Virginia, A ew a LE ae meee Rare Date 80,87 EE EE 62,63,70,71 Zygoceros Ehrenberg, 1841 bipons Ehrenberg, 18458 ne 79 tuomeyi Bailey, 1844 STRATIGRAPHIC POSITION & SAMPLE NUMBER Table 1.—Relative frequency of occurrence of marine diatom taxa in the Coosawhatchie equivalent beds, Thomas County, Georgia. Estimated relative frequency under 18 mm cover glass viewed at x 250 is defined as follows: A = abundant (at least one specimen in all fields of view); C = common (one specimen in many, but not all, fields of view); F = frequent (several specimens observed on slide but seen only in a few fields of view); R = rare (about one or two specimens observed on a slide). MARINE ASSEMBLAGES FETIO 4.5 m (Cus fii SEG R F F R RIR R E FIF FETOSS Gel mm Ole aes) 6469, 8.8 m (29 ft.) R E H F F R F FIF R R RIR FENDS MES A A F R R Prete LF a| E PF F RIFF R MERC A Nee ee RIFIF F R R FIFI|IRIRIF FRE RIRIR cic R F E | EE R RIR F BASE REST ODE iia F F R R FIRIR|RI|F R| F R R CIEC F SEI R RIR R R 6466, 14.6 m (48 ft.) |R|F F F F FI R|RIF R| F R R c|c F RIFIE R RIR R R 6465, 15.5 m (51 ft.) F F F R RIFIR|IR|F F|F R ETC R F FE er R RIR R R 64284, 18:6 mos fL) lee F F FIRIRIF RIF R RIRIR ole R F F|F|F R R|R F R Cru ae a a FR F F R FIR|IRIRIF R|F RIR C|F R F ELSE R RIR R vie feio NON HESS NA he F F RIRIRIRIEF R|F R R|R R c|c R F F|F|F R R|R F R 6461, 19.2 m (63 ft.) R F F F R R R E R FIF R F | | | | PREPARATION OF MANUSCRIPTS Bulletins of American Paleontology usually comprises two or more sep- arate monographs in two volumes each year. This series is a publication outlet for significant longer paleontological monographs for which high quality photo- graphic illustrations and the large quarto format are a requisite. Manuscripts submitted for publication in this monograph series must be typewritten, and double-spaced throughout (including direct quotations and ref- erences). All manuscripts should contain a table of contents, lists of text-figures and (or) tables, and a short, informative abstract that includes names of all new taxa. 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Size of lettering for text-figures. Journal of Paleontology, vol. 36, p. 1402. Gilbert Dennison Harris (1864 - 1952) Founder of the Bulletins of American Paleontology (1895) 6 ISBN 0-87710-397