Early Miocene 

Nonmarine Diatoms 

From the Pine Ridge Area, 

Sioux County, Nebraska

By GEORGE W. ANDREWS

CONTRIBUTIONS TO PALEONTOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 683-E

A description of an early Miocene nonmarine 

diatom assemblage from the Great Plains 

region and its stratigraphic and 

paleoecologic significance

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1 97 1
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

W. A. Radlinski, Acting Director

Library of Congress catalog-card No. 74-611764

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.O. 20402 - Price 50 cents (paper cover)

Stock Number 2401-1163
CONTENTS

Abstract- _-_--_____________.

Introduction_ _ _ -___-______.

Acknowledgments. _______

Pine Ridge diatomaceous beds. 

Location ________________

Lithology _ ______________

Locality A__________

Locality B_________.

Locality C_________.

Page

El 

1 

1 

1

1

2

2

3

3

Page

The Arikaree Group._________________________________ E4

Stratigraphy. _________-_-_-_-_------__-_-_-____.

Geologic age_____________________________________

Diatom assemblage._____-____^_______-__________--__.

Stratigraphic significance.___-_______-_-___---_--_.

Paleoecologic interpretation_____________-_-_-_-__.

Systematic descriptions_______________________________

Selected references___________________________________

Index.._ _______________-.--___-_-_-----__-_-----_-_-.

4

5

5

6

7

8

14

17

ILLUSTRATIONS

[Plates follow index]

PLATE 1. Melosira, Fragilaria, Eunotia, Cocconeis, Achnanthes, Anomoeoneis, Navicula, and Pinnularia. 

2. Pinnularia, Amphora, Cymbella, Gomphonema, and Hantzschia.

Page 

FIGURE 1. Index map showing location of the Pine Ridge area in Nebraska-_--_-______---_-_-___------------------_-_--- E 1

2. Map showing location of the Pine Ridge fossil diatom localities, Sioux County, Nebr.__________________________

3-6. Photographs:

3. Diatomaceous "white bed" at locality A_________________________.______________-_-_-_---_---_--_-_-----

4. Diatomaceous "white bed" at locality B______________________________-_________________---_----__---_-

5. Lower and upper "white beds" at locality C-_________._____________---_-_-___-_-_-_-_-_--_-_-_---------

6. Diatomaceous lower "white bed," at locality C_______-______-____-___-_-_-_-_-_-___-_-_-_--------------

7. Graph of ranges of living nonmarine diatom species compared with those of living mollusk species during the Tertiary 

Period- ____________________________________________________________________________________________

TABLE

TABLE 1. Relative abundance of diatoms in six collections from the Monroe Creek Sandstone _

Page

E6

ill

CONTRIBUTIONS TO PALEONTOLOGY

EARLY MIOCENE NONMARINE DIATOMS FROM THE 

PINE RIDGE AREA, SIOUX COUNTY, NEBRASKA

BY GEORGE W. ANDREWS

ABSTRACT

The Monroe Creek Sandstone of early Miocene age contains 

diatomaceous sediments at two stratigraphic levels in outcrops on 

the Pine Ridge escarpment, Sioux County, Nebr., 2 to 10 miles 

southwest of Crawford. The formation is dated as early Miocene 

by contained vertebrate faunas in the western Nebraska area; 

potassium-argon dating of the underlying Gering Formation and 

the overlying Harrison Sandstone limits the age of the Monroe 

Creek to between 21.3XlO6 and 25.6X106 years.

The Monroe Creek Sandstone contains what is here termed the 

"Pine Ridge diatom assemblage," consisting of 21 species and 

varieties of nonmarine diatoms. Seven of these species are new, and 

three others were known previously only from the late Eocene of 

Wyoming. Ten species and varieties are still living in modern 

nonmarine environments. The diatom assemblage suggests that 

deposition occurred in a shallow lake that had seasonal fluctuations 

in alkalinity. The diatomaceous sediments show evidence for 

deposition in a shallow, widespread playalike lake during temporary interruptions in Monroe Creek clastic sedimentation. The 

relatively large number of extinct species in the assemblage should 

be helpful in stratigraphic correlation once their ranges are more 

precisely known. The earliest occurrence of still-living species and 

varieties of nonmarine diatoms is also important in determining the 

age of diatom assemblages. The information available suggests 

that nonmarine diatom species may be somewhat longer ranging 

than other types of fossils. Thus, extinct diatoms may be more 

useful for stratigraphic correlation in Miocene and older assemblages, whereas the presence or absence of still-living forms may 

be more useful for correlation in Pliocene and later assemblages.

INTRODUCTION

Diatomiferous sediments crop out in two distinctive 

"white beds" in the Monroe Creek Sandstone, which is 

exposed along the Pine Ridge escarpment in eastern 

Sioux County, Nebr. These diatomaceous beds can be 

observed extensively in an area 2 to 10 miles southwest 

of Crawford, Nebr., but they are relatively inaccessible 

in most places because of the steep face of the escarpment. An early Miocene age is indicated by the vertebrate fossil faunas of the Monroe Creek and associated 

formations in western Nebraska.

The Monroe Creek Sandstone contains the oldest 

Tertiary nonmarine diatom assemblage yet discovered 

from the Great Plains area of North America. It is 

intermediate in age between the late Eocene assemblage 

from central Wyoming described by Lohman and 

Andrews (1968) and the late Miocene assemblage from

Kilgore, Nebr., described by Andrews (1970). The 

preservation of the Pine Ridge diatom assemblage, 

though not excellent, is adequate for a meaningful 

study. Its age is confirmed by the independent evidence 

of vertebrate paleontology. The Pine Ridge diatom 

assemblage from the Monroe Creek Sandstone provides 

valuable information for determining the stratigraphic 

ranges of Tertiary nonmarine diatoms, as it is the first 

early Miocene diatom assemblage from North America 

to be systematically studied.

The diatomiferous beds of the Monroe Creek Sandstone were first observed by the author in 1962. 

Samples for diatom study were collected during the 

summers of 1962 and 1966.

ACKNOWLEDGMENTS

Thanks are expressed to Kenneth E. Lohman, 

Division of Paleobotany, The Smithsonian Institution, 

and to Sergius H. Mamay, U.S. Geological Survey, for 

their critical review of the manuscript and their many 

helpful comments.

PINE RIDGE DIATOMACEOUS BEDS

LOCATION

Diatomaceous sediments of the Monroe Creek 

Sandstone crop out as two "white beds" in the otherwise 

drab strata on the Pine Ridge escarpment west of 

Crawford, Nebr. The location of the Pine Ridge area 

in western Nebraska is shown in the index map (fig. 1).

1__________lOfLLJValentine^ J^Q.!_JDAK°TA__ 9^

21 Pine Ridge diatom locality 

s!

KANSAS

5O O 5O 1OO MILES

I i i i i I_____________

FIGURE 1. Pine Ridge area in Nebraska.

El
E2 CONTRIBUTIONS TO PALEONTOLOGY

103°30'

42°40' -

T. 31 N. 2

Boundary of Fort Robinson Reservation

Hi

25 I 30

R. 53 W. R. 52 W.

FIGURE 2. Pine Ridge fossil diatom localities, Sioux County, Nebr.

The diatomaceous sediments were examined and collected at the three localities shown in detail in figure 2. 

Locality A is about one-half mile southeast of the lower 

end of Smiley Canyon on the northwest-facing cliff of 

Pine Ridge in the NWiNEiSWi sec. 14, T. 31 N. 

R. 53W., Sioux County. Locality B is farther to the 

southeast along the same ridge, on the end of the 

easternmost point of the high part of Pine Ridge between the Smiley Canyon and White River drainage 

basins in the SEJNEJSWJ sec. 14. Locality C is on the 

northeast side of a tributary valley to the White River, 

a short distance northeast and uphill from new (in 1967) 

U.S. Highway 20, downslope from a spirelike erosional 

remnant of Monroe Creek Sandstone, and in the 

NWiNWiNEJ sec. 21, T. 31N., R. 53W., Sioux 

County.

The outcrops at localities A and B can be reached 

from the point where old U.S. Highway 20 enters the 

lower end of Smiley Canyon by following Pine Ridge in 

a southeasterly direction about one-half and threequarters mile, respectively, and climbing nearly to the 

top of the ridge. Locality C is readily accessible by 

climbing a short distance from new U.S. Highway 20. 

The diatomiferous "white beds" crop out at an altitude 

of about 4,400 feet according to the Alliance, Nebr.,. 

1:250,000 map of the Army Map Service (1958), the 

only topographic map available for the region.

LITHOLOGY 

Locality A

The exposure at locality A is a basal 4-foot section of 

typical drab brownish-gray silty fine sand of the Monroe 

Creek Sandstone. The diatomaceous "white bed", 

which overlies the basal section, is a 1-foot layer of 

intensively bored and disturbed sediments, as illustrated 

in figure 3. This layer originally was deposited as a 

2-inch bed of white thinly laminated crinkly limestone 

overlain by a 10-inch bed of white moderately soft 

calcareous clay. After these original sediments were 

bored, the borings and interstices were filled by fine

FIGURE 3. Diatomaceous "white bed" at locality A indicated by 

hammer. USGS diatom localities 5972 and 5973.
MIOCENE NONMARINE DIATOMS, PINE RIDGE AREA, SIOUX COUNTY, NEBRASKA E3

sand and silt from the overlying sediments of typical 

Monroe Creek Sandstone lithology. Samples for diatom 

study were carefully selected to eliminate, as far as 

possible, these contaminating bore fillings. Although 

these fillings are not significantly younger than the 

enclosing matrix, they are less likely to contain diatoms 

than the finer grained original sediments. Both the 

laminated limestone (USGS diatom loc. 5972) and the 

softer overlying calcareous clay (USGS diatom loc. 

5973) contain identifiable diatoms. A larger assemblage 

was obtained from the limestone, probably because of 

better preservation.

Locality B

The "white bed" exposed at locality B, illustrated in 

figure 4, is approximately 2 feet thick. This section is 

correlative with that exposed at locality A, but the

laminated limestone is missing, and the diatomaceous 

sediments consist of white relatively soft silty clay. 

The white clay is again thoroughly bored, and the 

borings are filled with fine sand and silt typical of the 

overlying beds of the Monroe Creek Sandstone. A 

sample from a silty layer at the top of the "white bed" 

(USGS diatom loc. 5974) was unfossiliferous. Samples 

of carefully selected fragments of coherent white clay 

from the lower part of the bed (USGS diatom Iocs. 

5510 and 5975) contained a sparse assemblage of 

poorly-preserved diatoms.

Locality C

At locality C two distinct "white beds" are exposed, 

separated by about 12 feet of drab brownish-gray silty 

sandstone of typical Monroe Creek Sandstone lithology, 

as shown in figure 5. The lower "white bed", shown in

-j-Upper"white bed"

' " "ii>v

A*'-. Lower 

-*' . white bed"

FIGURE 4. Diatomaceous "white bed" at locality B occurs as a 

2-foot bed of soft silty clay immediately below the hard calcareous ledge. The overlying deposit is typical Monroe Creek 

Sandstone with pipy concretions. USGS diatom localities 5510, 

5574, and 5575.

FIGURE 5. Lower and upper "white beds" at locality C, as indicated. The interval between the two diatomaceous beds is 

about 12 feet thick.

figure 6, is about 8 to 10 inches thick, and it shows some 

variation in thickness and considerable evidence of 

boring. This bed can be divided into a lower 6-to 8-inch 

moderately hard white silty limestone (USGS diatom 

loc. 5976) and an upper 2-inch softer white silty 

calcareous clay (USGS diatom loc. 5977). This entire 

"white bed" is thoroughly bored and contains abundant 

calcareous internal molds of fossil gastropods. The lower 

"white bed" is underlain by mottled gray and brown 

fine sand which has a somewhat whitened appearance 

immediately below the "white bed." It is overlain by 

typical grayish-brown massive Monroe Creek Sandstone 

containing pipy concretions. The hard white gastropodbearing limestone contains the best preserved and most 

abundant diatom assemblage of those studied for this 

report. The upper calcareous clay contains a sparse 

assemblage.
E4 CONTRIBUTIONS TO PALEONTOLOGY

FIGURE 6. Diatomaceous lower "white bed" at locality C. The 

hammer head rests on hard white silty limestone (USGS diatom 

loc. 5976) and indicates the overlying soft white silty clay 

(USGS diatom loc. 5977).

The upper "white bed" exposed at locality C is 

irregular in thickness, and the white sediments themselves range within this small outcrop from 0 to 12 

inches in thickness. This variation appears to be due to 

erosion or planation of the upper surface of the bed. 

The white relatively soft calcareous clays are thoroughly 

bored, and the bore fillings are composed of typical 

Monroe Creek fine sand and silt similar to that of the 

overlying beds. Although the actual white sediments of 

this zone are discontinuous, they are underlain by a 

2-foot layer of mottled brown and light-gray sand, 

somewhat lighter in color at the top than typical 

Monroe Creek sediments. This bed seems to have lateral 

persistence, which may account for the widespread 

presence of the upper "white bed" in vertical scarp 

faces of the Pine Ridge. Fragments of white calcareous 

siltstone from the upper "white bed" at locality C 

(USGS diatom loc. 5978) contain a moderately varied 

diatom assemblage with fair preservation.

Although it appeared to the author that the single 

"white bed" at localities A and B correlated with the 

upper "white bed" of locality C, the only criterion for 

correlation was lithologic similarity. These diatomaceous beds are certain to be lenticular although they 

have a lateral extent of several miles in the Crawford 

area. The age difference of the diatomaceous beds is 

not great enough to be significant, and the paleoecological factors were probably similar during deposition 

of all of the diatom-bearing strata.

THE ARIKAREE GROUP

The lower Miocene strata now included in the 

Arikaree Group were first named and mapped by

Barton (1899, p. 743-747). However, Barton clearly 

distinguished the upper part of the modern Arikaree 

Group as his "Arikaree Formation" and recognized it 

as distinct from his underlying Gering Formation. He 

did point out (p. 743-744) that in some localities there 

is difficulty in identifying a definitive contact between 

his Gering and Arikaree Formations. Hatcher (1902, 

p. 116-117) divided the Arikaree Formation of Barton 

(1899) into two units: the Monroe Creek Beds and the 

Harrison Beds. Hatcher was inconsistent in his report, 

for on p. 118 he included the Gering Sandstone and the 

"Monroe Creek" in the "Arikaree" but then placed his 

"Harrison" as the lowermost unit in his overlying 

"Loup Fork".

The stratigraphic terminology of the lower Miocene 

rocks of western Nebraska was clarified by Schultz 

(1938), who redefined the Arikaree Formation of Barton 

(1899) as a group. Schultz (1938) included as subdivisions in his newly defined Arikaree Group the Gering 

Formation of Barton and the Monroe Creek Beds and 

Harrison Beds of Hatcher (1902). This classification 

was accepted by Lugn (1939, p. 1251-1253), and according to current terminology of the U.S. Geological 

Survey (Keroher and others, 1966, p. 132, 1497, 1686, 

2559), the Arikaree Group contains the following three 

units in ascending order: Gering Formation, Monroe 

Creek Sandstone, Harrison Sandstone.

STRATIGRAPHY

The Monroe Creek Sandstone, the middle unit of the 

Arikaree Group, contains what is here termed the 

"Pine Ridge diatom assemblage." This is named for 

the Pine Ridge, a 500-foot escarpment in northwestern 

Nebraska with a near vertical face that is composed 

mainly of Monroe Creek Sandstone. Thus, although 

this formation is extensively exposed for more than 150 

miles, the outcrops are so steep in many places that 

detailed study is difficult.

The Monroe Creek Sandstone is a massive, semiconsolidated brownish-gray silty fine sand. It is distinctly bedded, but this bedding is commonly inconspicuous because of the uniform lithology throughout 

the stratigraphic section. So-called "pipy" concretions 

are characteristic of the formation; they are locally 

restricted to certain layers, but in some places they are 

seemingly scattered indiscriminately in the massive 

outcrops. These concretions are typical Monroe Creek 

clastic sediments densely cemented by calcium carbonate; their hardness contrasts sharply with the semiconsolidated matrix material. The pipy concretions of 

the Monroe Creek Sandstone were studied by Schultz 

(1941), who reported that they have a preferred orientation in axial direction.
MIOCENE NONMARINE DIATOMS, PINE RIDGE AREA, SIOUX COUNTY, NEBRASKA E5

Lugn (1939, p. 1252) stated that the Monroe Creek 

Sandstone as exposed along the Pine Ridge between 

Crawford and Harrison, Nebr., ranges in thickness from 

about 285 to more than 360 feet. He also differentiated 

between two units of distinctive lithology in the formation. The lower part of the formation consists of from 

185 to about 220 feet of gray fine to medium sand, and 

the upper part consists of from 100 to nearly 150 feet of 

finer grained pink to buff sandy silt and clay. The Pine 

Ridge diatom assemblage occurs in two "white beds" of 

calcareous silt, fine sand, volcanic ash, and diatoms. 

One or both of the beds is exposed in various places on 

the cliffs of the Pine Ridge escarpment near Crawford, 

Fort Robinson, and Smiley Canyon. No measured 

stratigraphic sections of the Monroe Creek Sandstone 

have been published for this area. The diatomaceous 

"white beds" clearly fall within Lugn's upper unit of 

the formation in the finer grained and more distinctly 

bedded sediments.

GEOLOGIC AGE

The Monroe Creek Sandstone in western Nebraska 

is dated by contained vertebrate remains as well as by 

the fossil vertebrate faunas of the underlying and overlying formations. Fossil vertebrates are not as common 

in the Monroe Creek Sandstone as in the overlying 

Harrison Sandstone. Barton (1899, p. 747) reported 

that "vertebrate remains were collected in small numbers" from the Gering and Monroe Creek Formations. 

He also reported that fresh-water mollusks had been 

found in these beds, and that one particularly abundant 

mollusk fauna was found in a matrix of diatomaceous 

earth at a locality south of Gering, Nebr. The author 

has searched in vain for this diatomaceous bed in the 

area of Scottsbluff and the bluffs south of Gering. This 

deposit is probably similar to the diatom-bearing 

sediments of the Pine Ridge area studied for this 

report.

Hatcher (1902, p. 117) stated that the Monroe Creek 

Sandstone is generally barren of vertebrate fossils but 

that the beds near the top of the formation were known 

to contain Promerycochoerus. Cook and Cook (1933, 

p. 22-27) published a list of fossil vertebrates from the 

Monroe Creek beds of western Nebraska. They also 

suggested that the Gering and Monroe Creek Formations be assigned a late Oligocene age and that the 

Oligocene-Miocene boundary be drawn at the contact 

of the Monroe Creek Sandstone with the overlying 

Harrison Sandstone. This age was not adopted by other 

geologists, and Cook (1960, p. 204) accepted the consensus of an early Miocene age for the Gering and Monroe Creek Formations. A summary of the fossil oreodonts from the Arikaree Group of Nebraska was given

by Schultz and Stout (1961, p. 12) on the basis of several 

reports by Schultz and Falkenbach. The consensus 

from paleontological studies, mainly on fossil vertebrates, is that the Monroe Creek Sandstone is of early 

Miocene age.

The Arikaree Group of Nebraska has also been dated 

by the potassium-argon radiometric technique (Evernden and others, 1964, p. 178, 186-187). They gave a 

date of 25.6 X 10 6 years for a sample of volcanic ash 

11 feet above the base of the Gering Formation at 

Scottsbluff (KA 985). They also gave a date of 21.3 

X 10 6 years for a sample of tuff from the Harrison 

Sandstone at a level about 30 feet stratigraphically 

below the Agate fossil quarry (KA 481). No date is at 

present available specifically for the Monroe Creek 

Sandstone but these radiometric dates for the underlying and overlying formations limit well the age of the 

formation and its contained diatom assemblage.

In summary, the Pine Ridge diatom assemblage is 

relatively accurately dated by its stratigraphic position 

in the Monroe Creek Sandstone. The stratigraphic 

relations of the three formations of the Arikaree Group 

are not particularly complicated, and their relation to 

the underlying and overlying formations is well defined. 

The formations of the Arikaree Group are dated as 

early Miocene by the contained fossil vertebrate faunas. 

Furthermore, radiometric dating of adjacent formations 

limits the age of the diatom assemblage to between 

21.3 X 106 and 25.6 X 106 years.

DIATOM ASSEMBLAGE

The samples were prepared for diatom study following standard procedures of the USGS diatom laboratory. All the samples were calcareous, and they were 

first treated with hydrochloric acid to remove carbonates. The residue contained little organic matter, and 

the diatom-sized particles were concentrated by differential settling and decanting. The cleaned samples were 

mounted in Kollolith, a synthetic resin with a refractive 

index approximating that of Canada Balsam. Individual 

specimens were located by systematic traversing by a 

mechanical stage, and their locations in the strewn 

mounts were recorded as coordinates of the mechanical 

stage. The relative abundance of each species or variety 

of diatom in six studied assemblages is shown in table 1. 

The forms are listed according to estimated relative 

frequency on a glass slide viewed at 250 magnification, 

as follows: abundant, at least one specimen in all fields 

of view; common, one specimen in many (but not all) 

fields of view; frequent, several specimens observed on 

slide, but seen only in a few fields of view; rare, one or 

two specimens on slide. The exact geographic location
E6 CONTRIBUTIONS TO PALEONTOLOGY

TABLE 1. Relative abundance of diatoms from the Monroe Creek 

Sandstone

[A, abundant; C, common; F, frequent; R, rare]

USGS diatom locality

5972 5973 5510 5976 5977 5978

5975

Melosira italica (Ehrenberg) 

Kutzing__

Fragilaria brevistriata Grunow

var. inflata (Pantocsek) Hustedt. 

Eunotia sp. _

Achnanthes cincta Andrews, n. sp._ _ _ 

Anomoeoneis bicapitata Andrews, n.

<ar»

costata (Ktitzing) Hustedt

Navicula netroformis Andrews, n. sp._ 

Pinnularia brevicostata Cleve

elliptica Lohman and Andrews. _ 

fusana Andrews, n. sp

microstauron (Ehrenberg) Cleve_ 

scapha Lohman and Andrews. __ 

subrostrata Lohman and Andrews 

Amphora deflecta Andrews, n. sp.

Cymbella cistula var. maculata 

(Kiitzing) Van Heurck

lanceolata (Ehrenberg) Brun____ 

Gomphonema affine var. insignis 

(Gregory) Andrews

Hantzschia recta Andrews, n. sp.

--

R

R

--

--

R 

F 

F

F

F

__ __

R R

__ R

F __

__ R 

R 

.. F 

R __

R R

F __

_. R

F

A

C

R,

R

R

F 

F

F 

F

R 

R 

C

R

F

R

F

F

R,

--

--

R

R

R

R 

R

R,

R

R,

F

R,

R

--

R 

R 

R

R

F

R

and stratigraphic level of these collections are given in 

the discussion of the location and the lithology of the 

Pine Ridge diatomaceous beds. USGS diatom localities 

5510 and 5975 were placed together in table 1 because 

they represent collections made at different times from 

the same site and the same bed.

STRATIGRAPHIC SIGNIFICANCE

This report is the second part of a continuing stratigraphic study of Tertiary nonmarine diatom assemblages of the Great Plains region of North America. 

The first part was a report on a late Miocene diatom 

assemblage (Andrews, 1970), from the Valentine Formation of Lugn (1938) near Kilgore, Nebr. Also of 

significance to this study is the description of the late 

Eocene diatom assemblage from the Wagon Bed Formation of Wyoming by Lohman and Andrews (1968), 

even though that assemblage is technically outside the 

Great Plains region. The Pine Ridge assemblage of this 

report is intermediate in age between the Wagon Bed 

and Kilgore assemblages and somewhat bridges the 

extensive time gap between late Eocene and late 

Miocene. It also is from a part of the stratigraphic 

section where known diatom assemblages are rare 

probably because of poor preservation.

The Pine Ridge diatom assemblage contains 21 

recognized species and varieties of diatoms. Of these, 

seven species are new Achnanthes cincta, Anomoeoneis 

bicapitata, Navicula netroformis, Pinnularia, fusana,

Amphora deflecta, Amphora punctata, and Hantzschia 

recta. Three species Pinnularia elliptica, Pinnularia 

scapha, and Pinnularia subrostrata are known previously only from the Wagon Bed Formation (middle 

and late Eocene). The Pine Ridge assemblage has four 

species in common with the late Eocene, the aforementioned Pinnularias and the long-ranging Melosira 

italica. The Pine Ridge assemblage contains five diatom 

species and varieties in common with the late Miocene 

Kilgore assemblage Melosira italica, Fragilaria brevistriata, Pinnularia brevicostata, Cymbella cistula var. 

maculata, and Gomphonema affine var. insignis. All 

these are long-ranging forms still living in modern 

assemblages.

A significant difference from modern diatom assemblages is indicated by the relatively high number 

(about 50 percent) of extinct taxa in this early Miocene 

assemblage. Of equal importance is the lack of many 

modern diatom species, genera, and even families, 

which suggests that some of the modern forms might 

not yet have evolved by early Miocene time. It is impossible to say how typical the Pine Ridge assemblage 

is of early Miocene diatom assemblages or what percent 

it contains of early Miocene nonmarine diatoms to be 

found in other deposits. Furthermore, it is difficult to 

determine many ecological factors influencing the composition of this particular deposit. The significant 

differences between this assemblage and other studied 

assemblages, both fossil and modern, must be explored.

The only centric diatom observed in the Pine Ridge 

assemblage is Melosira italica, and the genera Cyclotella 

and Stephanodiscus, both common to modern assemblages, are absent. The subfamily Tabellarioideae is 

totally absent and the subfamily Fragilarioideae is 

represented by two closely related forms of Fragilaria 

brevistriata. The Eunotiaceae are represented by one 

problematical form of Eunotia which needs more study. 

Of the suborder Monoraphidineae, Cocconeis and Achnanthes occur only as single species. The common 

modern naviculoid genera Mastogloia, Caloneis, Neidium, Diploneis, and Stauroneis are absent; Navicula is 

represented by only one species, and Anomoeoneis by 

two species. The genus Pinnularia, with six species, 

shows more variety in forms than any other genus in 

the assemblage. Both Amphora and Cymbella are 

present in the Pine Ridge assemblage, and C. cistula 

var. maculata is also common in the late Miocene at 

Kilgore. Gomphonema is represented both here and at 

Kilgore by only one form, G. affine var. insignis, and the 

early Miocene specimens of this form in the Pine Ridge 

assemblage seem much less variable than the late 

Miocene specimens of the Kilgore assemblage. The
MIOCENE NONMARINE DIATOMS, PINE RIDGE AREA, SIOUX COUNTY, NEBRASKA E7

Epithemiaceae and the Surirellaceae are absent in 

both the Pine Ridge and Kilgore assemblages.

The Pine Ridge assemblage contains 12 genera of 

nonmarine diatoms and 21 species and varieties, 50 

percent of which are extinct. For comparison, the late 

Eocene Wagon Bed assemblage of Lohman and 

Andrews (1968) shows nine genera with 34 species and 

varieties, 80 percent extinct; the late Miocene Kilgore 

assemblage of Andrews (1970) shows 15 genera with 

45 species and varieties, 16 percent extinct; the late 

Pleistocene Hixton assemblage of Andrews (1966) 

shows 23 genera with 73 species and varieties, 3 percent 

extinct. Two trends are obvious from modern to progressively older assemblages: (1) the older the deposit, 

the greater the number of extinct species present, and 

(2) the older the deposit, the fewer species and varieties 

present. The decline in numbers of living taxa with age 

is somewhat greater than the decline in total numbers 

of taxa.

A comparison of the ranges of living nonmarine 

diatoms and marine mollusks for part of the Tertiary 

Period is shown in figure 7. The data on the diatoms are

50 40 30 20 10 0 

MILLION YEARS, BEFORE PRESENT

FIGURE 7. Ranges of living nonmarine diatom species 

compared with those of living mollusk species during 

the Tertiary Period.

drawn from these studies; data on the mollusks are 

adapted from Dunbar (1949, p. 397) and based on the 

classical Lyellian data of progressive Tertiary extinction. This chart is tentative and is a crude approximation of the actual situation. It does suggest, however, 

that nonmarine diatom species tend to be somewhat

longer ranging than marine mollusk species. The percentage of modern diatom species living in the Pleistocene and most of the Pliocene was high, and the extinct 

species in these deposits may be too few to be useful in 

stratigraphic correlation. Using extinct diatom species 

to determine the age of a deposit is more effective in 

Miocene or older deposits. It is increasingly apparent 

that successful stratigraphic correlation using nonmarine diatoms requires study of the total assemblage 

and consideration of the species absent as well as those 

present. Further study of other well-dated deposits 

will help determine the stratigraphic ranges of living 

and extinct species. The earliest geologic occurrence of 

living diatom species should be helpful in stratigraphic 

correlation, especially in the later Tertiary deposits.

PALEOECOLOGIC INTERPRETATION

The modern ecology of the 10 living species and 

varieties of nonmarine diatoms in the Pine Ridge 

assemblage provides some clues to the early Miocene 

paleoecology of the deposit. One assumes, of course, 

that these forms have preferred similar ecologic conditions from the early Miocene to the present, an 

assumption that cannot be proved. The relatively small 

percentage of centric and other planktonic species suggests deposition in a relatively shallow pond or sheet of 

water. This depositional environment is confirmed by 

the occurrence of such shallow-water species as Cocconeis placentula and Cymbella lanceolata. The evidence 

concerning alkalinity and salt content is conflicting. 

Only one species, Anomoeoneis costata, shows a preference for saline water, and Fragilaria brevistriata var. 

inflata and Cocconeis placentula show some preference 

for alkaline waters. On the other hand, Pinnularia 

brevicostata and P. microstauron prefer waters of low 

mineral content. Possibly the shallow ponds in which 

this assemblage was deposited fluctuated seasonally in 

alkalinity depending upon the inflow of fresh water. 

The abundance of lime in the diatom-bearing layers 

suggests that alkaline waters were present part of the 

time. Data are not sufficient to justify speculation 

about the water temperature during deposition of the 

diatomaceous sediments.

The physical stratigraphy, distribution, lithology, 

and fossil nonmarine mollusks of the diatom-bearing 

"white beds" also provide clues to the paleoecology of 

the deposit. The fresh-water limestone and calcareous 

clastic lithology suggest shallow-water deposition and 

moderate evaporation of water. The relatively thin 

beds suggest that the lakes in which the diatoms grew 

were of short duration. The distribution of the diatomaceous sediments over several miles suggests a thin 

sheet of water of considerable lateral extent.
E8 CONTRIBUTIONS TO PALEONTOLOGY

The diatomaceous "white beds" of the Monroe Creek 

Sandstone were deposited during interruptions in the 

deposition of fine silty sand. Probably little more was 

involved than temporary diversion of stream waters 

laden with clastic materials to another area. Perhaps 

a playa lake formed, having extremely shallow water 

and seasonal fluctuations. These lakes existed long 

enough for fresh-water limestones be deposited, for 

diatoms to live and be deposited, and for a mollusk 

assemblage, which caused extensive bioturbation of 

the sediments, to be disseminated throughout the lake 

basin. Conditions changed, and mixed clastic and 

carbonate sedimentation continued for a time; later, 

the lakes were filled by a fresh influx of typical Monroe 

Creek clastic material. Clastic sedimentation slowed 

twice in the Pine Ridge area, allowing deposition of the 

two diatomaceous "white beds." The diatom assemblages of these two beds are similar, indicating that 

ecologic conditions during both episodes were similar. 

This similarity in diatom assemblages and the stratigraphic proximity of the two diatom-bearing " white 

beds" indicate that a relatively short time elapsed 

between the deposition of these two beds.

SYSTEMATIC DESCRIPTIONS

The classification of diatoms used in this report is 

based on a proposed classification by K. E. Lohman 

(unpub. data) and was previously used in Lohman and 

Andrews (1968) and Andrews (1970). It follows the 

suggestions of Moore (1954) to the rank of class and 

follows in many respects the earlier classifications proposed by Schu'tt (1896), Karsten (1928), and Hendey 

(1937). As in previous reports, the treatment of the 

nomenclature in the generic and lower ranks is conservative, although this does not imply complete agreement 

with all the accepted nomenclature. Previously designated infraspecific taxonomic designations in current 

use are retained without enthusiasm, for reasons outlined by Andrews (1970, p. A8). To adhere to the 

binomial system as closely as possible, all new taxa are 

described by the author as species in this report.

The descriptions in this report refer to the specimens 

observed in the Pine Ridge diatom assemblage and do 

not necessarily reflect the total variation of each form. 

The descriptions of previously described species and 

varieties are brief; more complete diagnoses are in the 

general works cited in the synonymies. The first citation 

in each synonymy is that of the author of the taxon. 

The second citation includes references to the taxon in

the literature in chronologic order using the nomenclature accepted in this report. The third and remaining 

citations include synonyms, misidentifications, and 

incorrect attributions of authorship, also in chronologic 

order. References not examined by the author are 

marked with an asterisk. The comments on the ecology 

of the modern diatom taxa are adapted from Patrick 

and Reimer (1966), Hustedt (1927-30, 1931-59, 

1961-66), and Hustedt (1930). The known geologic 

ranges of the species and varieties are based on the 

results of this and previous studies; they may be modified by further investigations.

Kingdom PROTISTA Haeckel, 1866

Subkingdom PROTOCTISTA Hogg, 1860

Division CHRYSOPHYTA Pascher, 1914

Class DIATOMOPHYCEAE Rabenhorst, 1864

Order CENTRALES Schutt, 1896

Suborder DISCINEAE Kutzing, 1844

Family COSCINODISCACEAE KVltzing, 1844

Subfamily MELOSIROIDEAE Kutzing, 1844

Genus MELOSIRA Agardh, 1824

Melosira italica (Ehrenberg) Kutzing

Plate 1, figures 1, 2

Gaillonella italica Ehrenberg, 1836, Kgl. preuss. Akad. Wiss.

Berlin, Ber., 1836, p. 53. 

Melosira italica (Ehrenberg) Kutzing, 1844, Die kieselschaligen

Bacillarien oder Diatomeen, p. 55, pi. 2, fig. 6. 

Hustedt, 1927, Die Kieselalgen Deutschlands, Osterreichs,

und der Schweiz, pt. 1, p. 257-262, fig. 109. 

Lohman and Andrews, 1968, U.S. Geol. Survey Prof. Paper

593-E, p. 12, pi. 1, fig. 6. 

Andrews, 1970, U.S. Geol. Survey Prof. Paper 683-A, p. A9,

pi. 1, fig. 4. 

Gallionella crenulata Ehrenberg, 1843, Kgl. preuss. Akad. Wiss.

Berlin, Phys. Abh., 1841, p. 376, pi. 2, fig. I, 41; pi. 3, fig. I,

28; pi. 4, fig. I, 31. 

Melosira crenulata (Ehrenberg) Kutzing, 1833, Die kieselschaligen

Bacillarien oder Diatomeen, p. 55, pi. 2, fig. 8. 

Meloseira crenulata (Ehrenberg) Kutzing. Boyer, 1927, Acad. Nat.

Sci. Philadelphia Proc., v. 78, supp., p. 29.

Description. Valves cylindrical, bound in chains of 

frustules; margin denticulate; mantle finely punctate, 

puncta arranged in longitudinal, sometimes slightly 

spiral, rows; about 20 rows of puncta in 10/z. Diameter, 

about 7/i-15/z; height of single valve, about 10/z.

Remarks. M. italica is frequent in USGS diatom 

locality 5976 and rare in locality 5977.

M. italica is common in modern fresh-water environments as a pelagic form in lakes and as a littoral form 

in smaller bodies of water.

Known geologic range. From late Eocene to present.

Diameter of figured specimens (USGS diatom cat. 

Nos. 3702-25 and 3702-20), 15M, ll/*.
MIOCENE NONMARINE DIATOMS, PINE RIDGE AREA, SIOUX COUNTY, NEBRASKA E9

Order PENNALES Schutt, 1896

Suborder ARAPHIDINEAE Karsten, 1928

Family FRAGILARIACEAE Ki'tzing, 1844

Subfamily FRAGILARIOIDEAE KHtzing, 1844

Genus FRAGILARIA Lyngbye, 1819

Fragilaria brevistriata Grunow

Plate 1, figures 3, 4

Fragilaria brevistriata Grunow in Van Heurck, 1885, Synopsis des

diatomees de Belgique, p. 157. 

Hustedt, 1931, Die Kieselalgen Deutschlands, Osterreichs,

und der Schweiz, pt. 2, p. 168-170, fig. 676 a-e. 

Patrick and Reimer, 1966, Acad. Nat. Sci. Philadelphia

Mon. 13, p. 128-129, pi. 4, fig. 16. 

Andrews, 1970, U.S. Geol. Survey Prof. Paper 683-A,

p. 11, pi. 1, fig. 18, 19.

Description. Valve linear-lanceolate, often with subrostrate, rounded apices; transverse striae about 13 to 

14 in Wfj., marginal to a broad central hyaline area. 

Length, about 15//; width, about 4/z to 6/z.

Remarks. This species is usually seen in girdle view 

as chains of frustules, and well-oriented specimens in 

valve view are much less common. The transverse 

striae are of moderate length and more closely resemble 

the striae in the species as illustrated by Patrick and 

Reimer (1966) and Andrews (1970) than as illustrated 

by Grunow in Van Heurck (1881, pi. 45, fig. 32) and 

Hustedt (1931). The forms in the Pine Ridge assemblage resemble F. denticulata Lohman and Andrews 

(1968, p. 14, pi. 1, fig. 11, 12) but have slightly less 

robust and more closely spaced transverse striae. The 

species in this assemblage may be transitional between 

F. denticulata and later forms of F. brevistriata.

The species is abundant in USGS diatom locality 

5976.

Living representatives of the species are tolerant of 

a wide range of fresh-water environments.

Known geologic range. From early Miocene to 

present.

Length of figured specimens (USGS diatom cat. 

Nos. 3737-37 and 3737-38), both 15M .

Fragilaria brevistriata var. inflata (Pantocsek) Hustedt

Plate 1, figures 5, 6

Fragilaria inflata Pantocsek, 1902, Resultate Wiss. Erforsch.

Balatonsees, v. 2, pt. 2, sec. 1, p. 79, pi. 9, fig. 219-221. 

Fragilaria brevistriata var. inflata (Pantocsek) Hustedt, in Pascher,

1930, Die Susswasser-flora Mitteleuropas, no. 10, p. 145,

fig. 152. 

Patrick and Reimer, 1966, Acad. Nat. Sci. Philadelphia

Mon. 13, p. 129, pi. 4, fig. 16.

Description. Valve broadly fusiform with small 

rounded apices; short marginal transverse striae, 

about 14 in 10/z, with a large hyaline central area.

Length, about 12//; width, about 7/z.

Remarks. This variety occurs with the type, and 

it is difficult to separate the two when seen as chains of 

frustules in girdle view.

The variety is common in USGS diatom locality 5976 

and rare in locality 5978.

Living representatives of the variety prefer slightly 

alkaline waters.

Known geologic range. From early Miocene to 

present.

Length of figured specimens (USGS diatom cat. 

Nos. 3737-39 and 3702-42), 12M, 16M.

Suborder RAPHIDIOIDINEAE Karsten, 1928

Family EUNOTIACEAE Kutzing, 1844 

Subfamily EUNOTI01DEAE Kutzing, 1844

Eunotia sp.

Plate 1, figure 7

Description. Valve with slightly concave ventral 

side and more highly convex dorsal side; apices blunt, 

smoothly rounded, subrostrate; terminal nodules small, 

indistinct, on ventral side of valve near the apices. 

Length, about 28/z to 40/x; width, about 8/z.

Remarks. These specimens show a typical outline 

of Eunotia with a strong rim and terminal nodules. The 

center of the valve is hyaline and shows no discernable 

striae. This may result from poor preservation, striae 

too fine to be resolved with the light microscope, or no 

striae in this species. It is hoped that the structure of 

this form can be determined more fully in the future by 

the scanning electron microscope. This is the earliest 

known occurrence of the genus Eunotia in North 

America.

Rare in USGS diatom localities 5976 and 5978.

Known geologic range. Early Miocene.

Length of figured specimen (USGS diatom cat. No. 

3704-19), 29M .

Suborder MONORAPHIDINEAE Karsten, 1928

Family ACHNANTHACEAE Kutzing, 1844

Subfamily COCCONEOIDEAE Schutt, 1896

Genus COCCONEIS Ehrenberg, 1838

Cocconeis placentula Ehrenberg

Plate 1, figures 8, 9

Cocconeis placentula Ehrenberg, 1838, Die Infusionsthierchen als

vollkommene Organismen, p. 194.* 

Hustedt, 1933, Die Kieselalgen Deutschlands, Osterreichs,

und der Schweiz, pt. 2, p. 347-348, fig. 802a, b. 

Patrick and Reimer, 1966, Acad. Nat. Sci. Philadelphia

Mon. 13, p. 240-241, pi. 15, fig. 7.

Description. -Valve elliptical and relatively little 

arched; transverse striae about 20 in 10/z, finely punctate; pseudoraphe narrow, linear, not expanded into a
E10 CONTRIBUTIONS TO PALEONTOLOGY

central area; raphe valve not observed. Length, 2(V to 

27 n, width about 10/i to 14/i.

Remarks. The species is frequent in USGS diatom 

locality 5978 and rare in localities 5972, 5973, and 5975.

Living representatives of the species are epiphytic 

on aquatic plants and other objects and are common in 

circumneutral to alkaline waters.

Known geologic range. From early Miocene to 

present.

Length of figured specimens (USGS diatom cat. Nos. 

3704-12 and 3700-1), 27M, 24M .

Subfamily ACHNANTHOIDEAE Schutt, 1896 

Genus ACHNANTHES Bory, 1822

Achnanthes cincta Andrews, n. sp.

Plate 1, figures 10, 11

Diagnosis. Valve elliptical-lanceolate with rounded 

apices; striae about 18 in 10/i on both valves, slightly 

radiate. Both valves have a hyaline central belt or 

stauros in which two or three central striae are lacking. 

Raphe valve with thin straight raphe in narrow axial 

area; pseudoraphe valve with narrow pseudoraphe 

which expands to the margins of the valve at the central 

stauros. Length, about 21yu; width, about 5 to 6/i.

Holotype: USGS diatom catalog No. 3737-35 (pi. 1, 

figures 10, 11) length, 21/*; width, 5/t. From USGS 

diatom locality 5976.

Remarks. This species is readily distinguished by 

its elliptical-lanceolate shape and by the stauros on 

both the raphe and pseudoraphe valves. Most species 

of Achnanthes with a bilateral central hyaline area on 

the raphe valve do not show this feature on the pseudoraphe valve. Superficially A. cincta most closely resembles A. exigua var. elliptica Hustedt, but that variety 

is much smaller in size and has much finer striations.

Rare in USGS diatom localities 5972 and 5976.

Known geologic range. Early Miocene.

Suborder BIRAPHIDINEAE Karsten, 1928

Family NAVICULACEAE Kutzing, 1844

Subfamily NAVICUL01DEAE Kutzing, 1844

Genus ANOMOEONEIS Pfitzer, 1871

Anomoeoneis bicapitata Andrews, n. sp.

Plate 1, figures 12, 13

Diagnosis.- Valve small, linear, with broadly 

rounded, extremely capitate apices; raphe straight, 

hairlike; axial area narrow, bounded on each side by a 

single row of prominent puncta; central area defined by 

a slight asymmetric expansion of the axial area toward 

one side of valve; transverse striae radiate, about 24 in 

10/i, fine, formed of distinct puncta arranged in longitudinally undulating rows. Length, 26/i to 33/*; width, 

about 7fi.

Holotype: USGS diatom cat. No. 3704-16 (pi. 1, 

fig. 12), length, 26yu; width, 7/t. Paratype: USGS diatom 

catalog No. 3704-15 (pi. 1, fig. 13), length, 33/*; width, 

7/t. Both from USGS diatom locality 5978.

Remarks. This small species of Anomoeoneis is distinctive in its extremely bicapitate apices. In some 

specimens the ends of the valve have the appearance 

of rounded knobs attached to the main part by slender 

stalks. The punctation, typical of Anomoenoneis, is 

sometimes so fine that observation is difficult.

Rare in USGS diatom locality 5978.

Known geologic range. Early Miocene.

Anomoeoneis costata (Kutzing) Hustedt

Plate 1, figure 14

Navicula costata Kutzing, 1844, Die kieselschaligen Bacillarien

oder Diatomeen, p. 93, pi. 3, fig. 56. 

Anomoeoneis costata (Kutzing) Hustedt, 1959, Die Kieselalgen

Deutschlands, Osterreichs, und der Schweiz, pt. 2, p. 744-

747, fig. 1111. 

Patrick and Reimer, 1966, Acad. Nat. Sci. Philadelphia

Mon. 13, p. 376, pi. 32, figs. 3, 8.

Description. Valve elliptical-lanceolate with rounded 

apices showing very slight attenuation; axial area narrow, bounded by a single row of pronounced puncta; 

central area asymmetrical, expanding on one side to 

reach the margin of the valve; other areas between the 

axial area and margins filled with transverse striae, 

about 19 in 10/i, composed of undulating longitudinal 

rows of puncta. Length, about 38yu; width, about 11/i.

Remarks. A. costata, as it occurs in the Pine Ridge 

deposit, shows several minor differences from modern 

forms. It is somewhat smaller and more finely striated, 

and the axial area is narrow rather than wide. The Pine 

Ridge form also shows a slight tendency for attenuation 

of the apices. This Miocene form, however, does not 

differ significantly enough from the modern A. costata 

to be assigned to a separate species. Perhaps this 

Miocene form is ancestral to the two modern species, 

A. costata and A. sphaerophora, for it seems to show 

some characteristics of each species.

The species is rare in USGS diatom locality 5976.

Living representatives of the species occur in inland 

waters of medium to high salt concentration.

Known geologic range. From early Miocene to 

present.

Length of figured specimen (USGS diatom cat. No. 

3702-36), 38M .
MIOCENE NONMARINE DIATOMS, PINE RIDGE AREA, SIOUX COUNTY, NEBRASKA Ell

Genus NAVICULA Bory, 1822 

Navicula netroformis Andrews, n. sp.

Plate 1, figures 15-17

Diagnosis. Valve fusiform, lanceolate, with rostrate 

to subcapitate apices; transverse striae fine, 15 in lOju, 

somewhat radial and showing fine puncta; raphe fine 

and straight, occupying a narrow axial area, which 

expands into a smoothly rounded central area one-third 

to one-half the width of the valve; striae sometimes 

irregularly spaced marginal to the central area, but 

regularly shortened around the central area. Length, 

30M to 37M ; width, 9M to 10/*.

Holotype: USGS diatom catalog No. 3702-34 (pi. 1, 

fig. 15), length, 35M ; width, 9M. Paratype: USGS diatom 

catalog No. 3703-5 (pi. 1, fig. 16), length, 37M ; width, 

10/*. Paratype: USGS diatom catalog No. 3737-8 (pi. 1, 

fig. 17), length, 30//; width, 9/z. Holotype and second 

paratype from USGS diatom locality 5976; first paratype from locality 5977.

Remarks. N. netroformis closely resembles N. exigua 

var. capitata Patrick in general outline. It differs 

significantly, however, in its smoothly rounded hyaline 

central area. The apices of N. netroformis are also 

slightly less capitate than those of N. exigua var. capitata.

Frequent in USGS diatom locality 5976; rare in 

localities 5510, 5977, and 5978.

Known geologic range. Early Miocene.

Genus P1NNULARIA Ehrenberg, 1843 

Pinnularia brevicostata Cleve

Plate 1, figures 18, 19

Pinnularia brevicostata Cleve, 1891, Soc. pro Fauna et Flora

Fennica Acta, v. 8, no. 2, p. 25, pi. 1, fig. 5. 

Hustedt, in Pascher, 1930, Die Siisswasser-flora Mitteleuropas,

no. 10, p. 329-330, fig. 609. 

Patrick and Reimer, 1966, Acad. Nat. Sci. Philadelphia

Mon. 13, p. 623, pi. 60, fig. 1. 

Andrews, 1970, U.S. Geol. Survey Prof. Paper 683-A, p. 17,

pi. 3, fig. 2.

Description. Valve linear-elliptical with rounded 

apices; broad, hyaline axial area nearly half the width 

of the valve; striae short, 11 in 10/z, slightly radiate at 

center and convergent at the apices; raphe filamentous 

with prominent, slightly deflected central pores and 

terminating as a "question mark" near the apices. 

Length, about 65/x; width, about 15/z.

Remarks. The form occurring in this assemblage 

does not show any central swelling of the valve and 

shows only a slight suggestion of lateral expansion of 

the central area.

The species is frequent in USGS diatom locality 5976.

Living representatives of the species prefer cool 

waters of low mineral content.

Known geologic range. From early Miocene to 

present.

Length of figured specimens (USGS diatom cat. 

Nos. 3737-16 and 3702-24), 65M, 45M .

Pinnularia elliptica Lohman and Andrews

Plate 1, figures 20, 21

Pinnularia elliptica Lohman and Andrews, 1968, U.S. Geol. Survey 

Prof. Paper 593-E, p. 19, pi. 2, figs. 1, 2.

Description. Valve elliptical-lanceolate with narrowly rounded apices; some specimens show a slight 

tendency toward protracted apices; axial area narrow 

near the apices increasing gradually to about one-third 

to one-half the width of the valve at the center, hence, 

no distinct central area; transverse costae 11 to 16 in 

10/z, curved, strongly radiate near the center, slightly 

divergent near the apices; valve strongly curved 

laterally, with broad hyaline marginal band observed 

only in oblique view of specimens and fragments. 

Length of observed specimens, 100/z to 190//; width, 

about 30/z to 40/z.

Remarks. This species is poorly preserved in the 

Pine Ridge assemblage, and it is usually found as 

fragments. These fragments indicate that the upper 

size limits of the species may be much greater than 

indicated above, and large specimens may show fewer 

costae in 10/z than indicated above. Because the relatively large thin valves have such a high lateral convexity, they have often been broken by the normal 

processes of sedimentation and diagenesis.

The species occurs frequently in USGS diatom localities 5973 and 5976 and rarely in locality 5977.

Known geologic range. From late Eocene to early 

Miocene.

Length of figured specimens (USGS diatom cat. 

Nos. 3702-16 and 3702-29), about 166M, 190M .

Pinnularia fusana Andrews, n. sp.

Plate 1, figures 2 5-27

Diagnosis. Valve large, fusiform, lanceolate-elliptical with broad, rostrate apices; ends bluntly rounded; 

raphe straight, terminating in pronounced central 

pores; axial area narrow at the apices, increasing 

regularly to about one-third the width of the valve at 

the center; a rounded, slightly expanded central area is 

noticeable in some specimens but not in others; transverse costae, 9 to 10 in 10/z, radial near the center, 

divergent near the apices, sometimes showing an
E12 CONTRIBUTIONS TO PALEONTOLOGY

attenuated S-shape. Length, 68/u to 130/u; width, 22/u 

to 30/u.

Holotype: USGS diatom catalog No. 3737-10 (pi. 1, 

fig. 25), length, 78/u; width, 22/u. Paratype: USGS diatom catalog No. 3702-31 (pi. 1, fig. 26), length, 68/u; 

width, 22/u. Paratype: USGS diatom catalog No. 3702-4 

(pi. 1, fig. 27), length 87/u; width, 24/u. All from USGS 

diatom locality 5976.

Remarks. P. fusana has obvious affinities for both 

P. elliptica and P. subrostrata. It has a distinctive 

external shape, however, which differentiates it from 

these species. P. fusana differs from P. elliptica in 

having distinctly rostrate protracted apices. It differs 

from P. subrostrata in the markedly elliptical lateral 

margins, which contrast with the weakly elliptical or 

subparallel lateral margins of the latter species. Some 

specimens of P. fusana show no expanded central area 

typical of P. elliptica; others show a definitely expanded 

central area similar to that of P. subrostrata.

Frequent in USGS diatom locality 5976; rare in 

locality 5977.

Known geologic range. Early Miocene.

Pinnularia microstauron (Ehrenberg) Cleve

Plate 1, figures 22-24

Stauroptera microstauron Ehrenberg, 1843, Kgl. preuss. Akad.

Wiss. Berlin, Phys. Abh., 1841, p. 423, pi. 1, fig. IV, 1. 

Pinnularia microstauron (Ehrenberg) Cleve, 1891, Soc. pro Fauna

et Flora Fennica Acta, v. 8, no. 2, p. 28. 

Hustedt, in Pascher, 1930, Die Siisswasser-flora Mitteleuropas,

no. 10, p. 320, fig. 582.

Patrick and Reimer, 1966, Acad. Nat. Sci. Philadelphia 

Mon. 13, p. 597-598, pi. 55, fig. 12.

Description. Valve linear with broadly rostrate 

apices; axial area narrow, tapering toward the central 

area, which expands to the margins of the valve; striae 

about 13 in 10/u, markedly radiate near the center, but 

becoming convergent toward the apices. Length, 32/u 

to 60/u; width, 8/u to 10/u.

Remarks. P. microstauron has affinities with P. 

brebissonii, reported by Lohman and Andrews (1968, 

p. 18-19) from the late Eocene of Wyoming.

The species is rare in USGS diatom localities 5972, 

5975, 5976, 5977, and 5978.

P. microstauron is tolerant of a variety of fresh-water 

environments, but seems to prefer oligotrophic, slightly 

acid waters.

Known geologic range. From early Miocene to 

present.

Length of figured specimens (USGS diatom cat. 

Nos. 3737-31, 3702-47, 3737-27), 35/u, 40/u, 60/u.

Pinnularia scapha Lohman and Andrews 

Plate 2, figures 1, 2

Pinnularia scapha Lohman and Andrews, 1968, U.S. Geol. Survey 

Prof. Paper 593-E, p. 20, pi. 2, fig. 5.

Description. Valve elliptical with bluntly rounded 

apices; transverse costae 9 to 10 in 10/u, radial at the 

center but convergent near the apices; axial area narrow, expanding at the central area into a transverse 

fascia, more or less quadrangular and oriented with 

one diagonal parallel to the longitudinal axis. Length, 

41/u to 59/u; width, 14/u to 15/u.

Remarks. This species shows affinities for P. subrostrata, which is more common in the Pine Ridge 

assemblage. It differs mainly in its smoothly rounded 

apices and somewhat more quadrangular central area. 

The quadrangular central area seems less consistently 

well developed in the Pine Ridge specimens than in the 

late Eocene form described by Lohman and Andrews 

(1968, p. 20).

The species is frequent in USGS diatom locality 5972 

and rare in localities 5510, 5976, and 5978.

Known geologic range. From late Eocene to early 

Miocene.

Length of figured specimens (USGS diatom cat. 

Nos. 3699-18 and 3702-35), 48/u and 50M .

Pinnularia subrostrata Lohman and Andrews

Plate 2, figures 3-5

Pinnularia subrostrata Lohman and Andrews, 1968, U.S. Geol. 

Survey Prof. Paper 593-E, p. 21, pi. 2, fig. 16.

Description. Valve linear-elliptical with broadly 

rounded subrostrate apices; lateral margins straight to 

slightly convex; axial area narrow, expanding rapidly 

near the center into a rounded or diagonally subquadrangular central area; transverse costae, 9 to 12 in 10/u, 

radial at center, convergent near apices. Length, 39/u 

to 108/u; width, 13/u to 20/u.

Remarks. This species is distinguished from P. 

scapha mainly by its more linear outline and its broad 

subrostrate apices. It shows considerable variation in 

outline and shape of the central area. It is more linear 

and less biconvex than P. fusana.

P. subrostrata is common in USGS diatom locality 

5976, frequent in localities 5510, 5972, 5973, 5975, and 

rare in 5977 and 5978. The preservation of specimens 

is good.

Known geologic range. Late Eocene to early Miocene.

Length of figured specimens (USGS diatom cat. 

Nos. 3699-19, 3737-11, 3699-13), 54M, 60/u, 52/u.
MIOCENE NONMARINE DIATOMS, PINE RIDGE AREA, SIOUX COUNTY, NEBRASKA E13

Family CYMBELLACEAE Agardh, 1830 

Genus AMPHORA Ehrenberg, 1840

Amphora deflecta Andrews, n. sp.

Plate 2, figures 6, 7

Diagnosis. Frustule elliptical with protracted truncated apices; connective zone about one-third the width 

of the frustule, hyaline, with vague, ill-defined longitudinal markings; valve half elliptical-lanceolate with 

smoothly elliptical dorsal side and nearly straight 

ventral side; apices protracted, capitate, deflected 

ventrally; raphe fine, straight, near the ventral side of 

the valve, deflected ventrally near the apices, and 

having small central pores deflected dorsally; axial 

area narrow, not expanding into a central area; transverse striae fine, about 30 in 10/*, punctate, slightly 

radial, filling the entire lateral area. Length, 26 p to 34,u; 

width of valve, about 4/x to Q^.

Holotype: USGS diatom catalog No. 3700-9 (pi. 2, 

fig. 6), length, 34M ; width of valve, 6M ; from USGS 

diatom locality 5973. Paratype: USGS diatom catalog 

No. 3699-20 (pi. 2, fig. 7), length, 26M ; width of frustule, 

15M ; from USGS diatom locality 5972.

Remarks. A. deflecta is readily distinguished by its 

ventrally deflected capitate apices and fine uniform 

striation.

Frequent in USGS diatom locality 5972 and rare in 

locality 5973.

Known geologic range. The early Miocene.

Amphora punctata Andrews, n. sp.

Plate 2, figures 8-10

Diagnosis. Valve lanceolate with slightly produced 

sub rostrate apices; ventral margin straight; dorsal 

margin smoothly rounded until slightly deflected near 

the apices; raphe straight, located close to the ventral 

margin; transverse striae fine but sharp, about 20 in 

lO^i, continuous near both the raphe and the dorsal 

margin, but broken in the center of the valve into 

elongate puncta aligned in irregularly undulating 

longitudinal rows. Length, 35^ to 54^; width, lljt to

Holotype: USGS diatom catalog No. 3443-7 (pi. 2, 

fig. 8), length, 48M ; width, 13M . Paratype: USGS diatom 

catalog No. 3443-13 (pi. 2, fig. 9), length, 47M ; width, 

HM. Paratype: USGS diatom catalog 3702-33 (pi. 2, 

fig. 10), length, 40M ; width, 12M .

Remarks. A. punctata does not seem to resemble 

closely any of the previously described nonmarine 

forms of Amphora. It is distinguished by its halflanceolate shape, slightly rostrate apices, and undulating rows of transversely elongated puncta.

Rare in USGS diatom localities 5510 and 5976. 

Knoivn geologic range. Early Miocene.

Cymbella cistula var. maculata (Kulzing) Van Heurck

Plate 2, figures 11-13

Frustulia maculata Kiitzing, 1834, Algarum aquae dulcis Germanicarum, Dec., no. 85.*

Cymbella cistula var. maculata (Kiitzing) Van Heurck, 1880,

Synopsis des diatomees de Belgique, p. 64, pi. 2, fig. 16, 17.

Cleve, 1894, Kgl. svenska vetensk. akad. Handl., v. 26,

no. 2, p. 173. 

Hustedt, in Pascher, 1930, Die Siisswasser-flora Mitteleuropas,

no. 10, p. 363, fig. 676b. 

Andrews, 1970, U.S. Geol. Survey Prof. Paper 683-A, p. A19,

pi. 3, fig. 10.

Cymbella cistula maculata (Kiitzing) A. Schmidt. Boyer, 1927, 

Acad. Nat. Philadelphia Proc., v. 79, supp., p. 280.

Description. Valve asymmetric with markedly convex dorsal side and curved raphe; ventral side basically 

concave, but with enough central swelling so that the 

side becomes slightly convex; axial area narrow, without 

noticeable expansion into a central area; striae, 9 to 10 

in 10/i at center, more closely spaced near the apices, 

coarsely punctate, radiate throughout the valve. 

Length, 28/x to 57/x; width, about W/JL to 12/i.

Remarks. The species observed in this assemblage 

is a bit less asymmetric than previously described late 

Miocene and modern forms. The type variety was not 

observed, and only the variety maculata occurs in this 

deposit.

C. cistula var. maculata is frequent in USGS diatom 

localities 5972, 5973, 5976, and 5978; it is rare in locality 

5977.

Living representatives of the variety are common 

and widespread in fresh-water environments.

Known geologic range. From early Miocene to 

present.

Length of figured specimens (USGS diatom cat. 

Nos. 3702-5, 3702-28, 3704-2), 49M , 44M, 43M .

Cymbella lanceolata (Ehrenberg) Brun

Plate 2, figures 14, 15

Cocconema lanceolatum Ehrenberg, 1838, Die Infusionsthierchen

als vollkommene Organismen, p. 224.* 

Cymbella lanceolata (Ehrenberg) Brun, 1880, Diatomees des Alpes

et du Jura, p. 57, pi. 3, fig. 19. 

Boyer, 1927, Acad. Nat. Sci. Philadelphia Proc., v. 79, supp.,

p. 279. 

Cymbella (Cocconema} lanceolatum (Ehrenberg) Van Heurck, 1880,

Synopsis des diatomees de Belgique, pi. 2, fig. 7. 

Cymbella lanceolata (Ehrenberg) Van Heurck. Hustedt, in Pascher,

1930, Die Siisswasser-flora Mitteleuropas, no. 10, p. 364,

fig. 679.

Description. Valve half-lanceolate with convex dorsal side and nearly straight ventral side with slight
E14 CONTRIBUTIONS TO PALEONTOLOGY

central swelling; apices rounded; raphe slightly arched 

and centered in a narrow axial area which does not 

expand into a noticeable central area; transverse striae, 

11 to 12 in 10^, composed of distinct puncta. Length, 

68^ to 80^; width, about 15^ to 16^.

Remarks. This species has obvious affinities with 

C. cistula var. maculata, but it is larger and has a more 

elongate, lanceolate outline. It is difficult to determine 

whether Brun or Van Heurck deserve credit for revising 

the species, as both placed Cocconema lanceolatum in the 

genus Cymbella in 1880.

C. lanceolata is rare in USGS diatom localities 5975, 

5976, and 5978.

Living representatives of the species are common in 

fresh water, especially as a littoral form in standing 

water.

Known geologic range. From early Miocene to 

present.

Length of figured specimens (USGS diatom cat. 

Nos. 3704-17 and 3702-5), 74M , 80M .

Family GOMPHONEMACEAE Kutzing, 1844 

Genus GOMPHONEMA Agardh, 1824

Gomphonema affine var. insignis (Gregory) Andrews

Plate 2, figures 16-18

Gomphonema insigne Gregory, 1856, Micros. Soc. Quart. Jour.,

v. 4, p. 12, pi. 1, fig. 39. 

Grunow, in Van Heurck, 1880, Synopsis des diatomees de

Belgique, pi. 24, fig. 39-41. 

Gomphonema affine var. insignis (Gregory) Andrews, 1970, U.S.

Geol. Survey Prof. Paper 683-A, p. 20, pi. 3, figs. 12-16. 

Gomphonema lanceolatum var. insignis (Gregory) Cleve, 1894, Kgl.

svenska vetensk. akad. Handl., v. 26, no. 2, p. 183. 

Hustedt, in Pascher, 1930, Die Siisswasser-flora Mitteleuropas,

no. 10, p. 376, fig. 701. 

Gomphonema lanceolatum insigne (Gregory) Cleve. Boyer, 1927,

Acad. Nat. Sci. Philadelphia Proc., v. 79, supp., p. 295.

Description. Valve lanceolate-clavate to almost lanceolate, rounded on upper end, but tapering to a somewhat more acutely pointed lower end; axial area about 

one-fourth the width of the valve; asymmetrical central 

area formed by a few striae lacking on one side of valve; 

single stigma, not prominent, on opposite side from 

central area; transverse striae about 10 in 10/x. finely 

punctate. Length, 34^ to 58^; width, 8^ to 10/z.

Frequent in USGS diatom locality 5976.

The variety is common in a wide range of modern 

fresh-water environments.

Known geologic range. From early Miocene to 

present.

Length of figured specimens (USGS diatom cat. 

Nos. 3702-19, 3702-39, and 3702-45), 55M , 52M, 54M .

Family NITZSCHIACEAE Grunow, 1860

Subfamily NITZSCHIOIDEAE Grunow, 1860

Genus. HANTZSCHIA Grunow, 1880

Hantzschia recta Andrews, n. sp.

Plate 2, figures 19-22

Diagnosis. Valve linear, long and narrow; ventral 

margin straight to slightly convex; dorsal margin 

nearly straight at center and curving convexly toward 

the apices in some specimens, slightly convex throughout its length in other specimens; apices attenuated, 

terminating in small, rounded, subcapitate ends; keel 

puncta about 5 to 8 in 10^, irregularly spaced; transverse striae fine, about 22 in 10^. Length, 66 to 83^; 

width, about 6^ to 8^.

Holotype: USGS diatom catalog No. 3737-28 (pi. 2, 

fig. 19), length, 83M ; width, 8M . Paratype: USGS diatom 

catalog No. 3737-17 (pi. 2, fig. 20), length, 72M ; width, 

SM. Paratype: USGS diatom catalog No. 3737-23 (pi. 2, 

figs. 21, 22), length, 80^; width, 6M .

Remarks. This species differs from modern freshwater species of Hantzschia in lacking the arcuate outline caused by a concave ventral margin. The transverse 

striae are also finer and more closely spaced.

The species is frequent in USGS diatom locality 5976.

Known geologic range. Early Miocene.

SELECTED REFERENCES

Andrews, G. W., 1966, Late Pleistocene diatoms from the Trempealeau Valley, Wisconsin: U.S. Geol. Survey Prof. Paper

523-A, 27 p., 3 pis. 

 1970, Late Miocene nonmarine diatoms from the Kilgore

area, Cherry County, Nebraska: U.S. Geol. Survey Prof.

Paper 683-A, 24 p., 3 pis. 

Brun, Jacques, 1880, Diatomees des Alpes et du Jura, et de la

region Suisse et Frangaise des environs de Geneve: Paris,

145 p., 9 pis. 

Cook, H. J., 1960, New concepts of Late Tertiary major crustal

deformations in the Rocky Mountain region of North

America: Internat. Geol. Cong., 21st, Copenhagen, 1960,

Kept., pt. 12, p. 198-212. 

Cook, H. J., and Cook, M. C., 1933, Faunal lists of the Tertiary

Vertebrata of Nebraska and adjacent areas: Nebraska Geol.

Survey, Paper 5, 58 p. 

Darton, N. H., 1899, Preliminary report on the geology and water

resources of Nebraska west of the one hundred and third

meridian: U.S. Geol. Survey Ann. Kept. 19, pt. 4, p. 719-785,

pis. 74-117. 

Dunbar, C. O., 1949, Historical geology: New York, John Wiley

and Sons, 567 p. 

Evernden, J. F., Savage, D. E., Curtis, G. H., and James, G. T.,

1964, Potassium-argon dates and the Cenozoic mammalian

chronology of North America: Am. Jour. Sci., v. 262, no. 2,

p. 145-198. 

Hatcher, J. B., 1902, Origin of the Oligocene and Miocene deposits

of the Great Plains: Am. Philos. Soc. Proc., v. 41, no. 169,

p. 113-131.
MIOCENE NONMARINE DIATOMS, PINE RIDGE AREA, SIOUX COUNTY, NEBRASKA E15

Hendey, N. I., 1937, The plankton diatoms of the southern seas: 

Discovery Reports, v. 16, p. 151-364, pis. 6-13.

Hustedt, Friedrich, 1927-30, 1931-59, 1961-66, Die Kieselalgen 

Deutschlands, Osterreichs, und der Schweiz, Band 7 of 

Rabenhorst, G. L., Kryptogamenflora ***: Leipzig, Akademische Verlagsgesellschaft, pt. 1, 920 p., 542 figs., 1927-30; 

pt. 2, 845 p., 637 figs., 1931-1959; pt. 3, lieferungen 1-4, p. 

1-816, figs. 1180-1788, 1962-66.

 1930, Bacillariophyta (Diatomeae), Heft 10 of Pascher, 

Adolf, ed., Die Siisswasser-flora Mitteleuropas: Jena, Gustav 

Fischer, 466 p., 875 figs.

Karsten, George, 1928, Bacillariophyta (Diatomeae), in Engler, 

Adolf, Die natiirlichen Pflanzenfamilien. Band 2, Peridineae 

(Dinoflagellatae), Diatomeae (Bacillariophyta), Myxomycetes: Leipzig, Wilhelm Engelmann, p. 105-303, 329 figs.

Keroher, G. C., and others, 1966, Lexicon of geologic names of the 

United States for 1936-1960: U.S. Geol. Survey Bull. 1200, 

3 v., 4341 p.

Lohman, K. E., and Andrews, G. W., 1968, Late Eocene nonmarine 

diatoms from the Beaver Divide area, Fremont County, 

Wyoming: U.S. Geol. Survey Prof. Paper 593-E, 26 p., 2 pis.

Lugn, A. L. 1938, The Nebraska State Geological Survey and the 

"Valentine problem": Am. Jour. Sci., 5th ser., v. 36, no. 213,

p. 220-227.

1939, Classification of the Tertiary System in Nebraska:

Geol. Soc. America Bull, v. 50, no. 8, p. 1245-1275, 1 pi. 

Moore, R. C., 1954, Kingdom of organisms named Protista: Jour.

Paleontology, v. 28, no. 5, p. 588-598. 

Patrick, Ruth, and Reimer, C. W., 1966, The diatoms of the

United States, v. 1: Acad. Nat. Sci. Philadelphia Mon. 13,

688 p., 64 pis. 

Schutt, Franz, 1896, Bacillariales (Diatomeae), in Engler, Adolf,

and Prantl, K. A. E., Die natiirlichen Pflanzenfamilien:

Leipzig, pt. 1, Abt. Ib, p. 31-153, 282 figs. 

Schultz, C. B., 1938, the Miocene of western Nebraska: Am. Jour.

Sci., 5th ser., v. 35, p. 441-444. 

 1941, The pipy concretions of the Arikaree: Nebraska

Univ. State Mus. Bull, v. 2, no. 8, p. 69-82. 

Schultz, C. B., and Stout, T. M., 1961, Field conference on the

Tertiary and Pleistocene of western Nebraska: Nebraska

Univ. State Mus. Spec. Pub. 2, 55 p. 

Van Heurck, Henri, 1880-85, Synopsis des diatomees de Belgique:

Anvers, Atlas, pis. 1-30, 1880; pis. 31-77, 1881; pis. 78-103,

1882; pis. 104-132, 1883; text, index to Atlas, 120 p., 1884;

text, description, 235 p., 1885. 

Wood, H. E., 2d, and others, 1941, Nomenclature and correlation

of the North American continental Tertiary: Geol. Soc.

America Bull., v. 52, no. 1, p. 1-48, 1 pi.

INDEX

Page 

Achnanthaceae._--______-__---___-_____ E9

Achnanthes----------------------------- 6, 10

cincta __________________________6, 10, pi. 1

exigua elliptica-- ____________________ 10

afflne insignis, Gomphonema.............. 6, H

Agate fossil quarry..___________________ 5

An.phora. ______________________6, 12, 13

deflecta. _____________________-__6,12, pi. 2

pM?ictata____---.________________6,13, pi. 2

-4nojnoeoneis-_-----------------------__- 6, 10

bicapitata.------------ ______ ____6,10, pi. 1

costata.......... _________.____6, 7, 10, pi. 1

sphaerophora-- _ ___________________ 11

Araphidineae_----_-_-_-__-_____________ 8

Arikaree Group.---__-_-------------_--- 4, 5

B

bicapitata, Anomoeoneis. ________-----___- 6, 10

Biraphidineae _ ________________________ 10

brebissonii, Pinnularia................... 12

brevicostata, Pinnularia................-.6, 7, 11

brevistriata, Fragilaria. ___________________ 6,9

inflata, Fragilaria.. .... ______________ 6, 7, 9

[Italic page numbers indicate major references and descriptions]

Page 

Eunotiaceae.-----------------.--------- E6, 9

Eunotioideae. --_-------_--------------_ 9

exigua elliptica, Achnanthes.-------------- 10

capitata, Navicula- ______..___._-.-_- 11

Caloneis .... ............

capitata, Navicula exigua . 

Centrales ______________

Chrysophyta_ __________

........... 6

........... 11

___________ 8

___________ 8

cincta, Achnanthes... ____________________ 6, 10

cistula maculata, Cymbella. .............. 6, 13, 14

Coccon_is______-__--____________________ 6, 9

placentula __ _.________________6, 7, 9, pi. 1

Cocconema lanceolatum.. ................. 13, 14

(Cocconema) lanceolatum, Cymbella......... 13

Cocconeoideae. -----_______-_--------.__ 9

Coscinodiscaceae- ---____--______.__-_-__ 8

costata, Anomoeoneis _ _ _ _ ....... _________6, 7, 10

crenulata, Gallionella. .................... 8

Melosira ........................... 8

Cyclotella _ _ ._----.____________________ 6

C_-jnbeMa_______________________________ 6, 14

cistula maculata.... ______ ____6, 13, 14, pi. 2

ZawceoZata_----________________6, 7, 13, pi. 2

(Cocconema) lanceolatum............. 13

Cymbellaceae _ ________________________ 12

D

Darton (1899), quoted_________________ 5

deflecta, Amphora....--_-______-_-------_ 6, 12

denticulata, Fragilaria.................... 9

Diatomophyceae ________________________ 8

Diploneis............................... 6

Discineae ____-----.____________________ 8

E

elliptica, Achnanthes exigua............... 10

elliptica, Pinnularia.. __________________6, 11, 12

Epithemiaceae. _________________________ 7

Eunotia................................ 9

sp.______________________________6, 9, pi. 1

F

Fragilaria.-.---..--.............------- 8

brevistriata.............. _________6, 9, pi. 1

inflata_..._________________6, 7, 9, pi. 1

denticulata.. ________________________ 9

inflata...-----.....--.............. 9

Fragilariaceae. _________________________ 8

Fragilarioideae________-------------_-- 6, 8

Frustulia maculata....................... 13

fusana, Pinnularia...... _______________6, 11, 12

Gaillonella italica... _____________________ 8

Gallionella crenulata..................... 8

Gering Formation.--____________________ 4, 5

Gomphonema. . _ _ _______________________ 6, 14

affine insignis....................6, H, pi. 2

insigne...--_---_____________--.-_-- 14

lanceolatum insigne. _________________ 14

insign is ________________________ 14

Gomphonemaceae. ______________________ 14

Great Plains area--__________________--. 1

H

Hantzschia _____________________________ 14

recta........________________6,1-4, pi. 2

Harrison Sandstone, ____________________ 4, 5

Hixton assemblage-______________----._- 7

inflata, Fragilaria ....................... 9

brevistriata _________________________ 6, 7, 9

insigne, Gomphonema_ ___________________ 14

insignis, Gomphonema affine.------------- 6,1-4

lanceolatum- ________________________ 14

italica, Gaillonella _______________________ 8

MetosiYa___________________________ 6, S

K

Kilgore assemblage._____________________ 6,7

lanceolata, Cymbella. ____________ _______ _6, 7, 13

lanceolatum, Cocconema.................. 13,14

Cymbella (Cocconema)... _____________ 13

insignis, Gomphonema_______________ 14

M

maculata, Frustulia-.-.. _________________ 13

Cymbella cistula. __________________6,13, 14

Mastogloia _____----___-_____________--. 6

Meloseira crenulata...................... 8

Melosira _______________________________ 8

crenwZata ___________________________ 8

_taZica_-----_-___________________6, S, pi. 1

Page 

Melosiroideae_-_----_-----------------_- E8

microstauron, Pinnularia... _-_-------__-_6, 7,12

Stauroptera,. __-______--___-_-_----- 12

Monoraphidineae_--__--------_--------- 6, 9

Monroe Creek Sandstone.--..-----I, 2, 3, 4, 5, 8

N

Navicula..............................- 6, 10

exigua capitata... ... ---------------- 11

netroformis---.-.................6,10, pi. 1

Naviculaceae. _____-_____-_---_--------_ 10

Naviculoideae __-_--____-------------_-_ 10

Neidium _.__---_---______-_--__-------- 6

netroformis, Navicula. __________._---_--_ 6,10

Nitzschiaceae. -------------------------- 14

Nitzchioideae. . _____________----_---_--- 14

Pennales. ___-------_____-----_-------_- 8

Pine Ridge assemblage.-.-----.------!, 4, 5, 6, 8

Pine Ridge escarpment._____-----.---_-- 1, 5

Pinnularia......--......--..----------- 6, 11

brebissonii- _----___---_-_-----_----_ 12

brevicostata __-______-_----___6, -7,11, pi. 1

elliptica-------....-----.....6, 11, 12, pi. 1

fusana----.________. . 6,11, 12, pi. 1

microstauron..-------- _------_6, 7,12, pi. 1

scapha...................-..----6, 12, pi. 2

subrostrata. ____________-_-_-6,12, pi. 2

Pipy concretions_________-_____-_---_-_- 4

placentula, Cocconeis.---------- ___-_-__-_ 6, 7, 9

Promerycochoerus--.- -------------------- 5

Protista________________---.---_-- 8

Protoctista_.-__--_-_-___--------- _ 8

punctata, Amphora--., __________________ 6,13

R

Raphidioidineae. _ _ _______-_-__---_--__ 9

recta, Hantzschia--.................-.--. 6, 14

scapha, Pinnularia-------....----------- 6, 12

Smiley Canyon.________________________ 2

sphaerophora, Anomoeoneis --------------- 11

Stauroneis------------------------------ 6

Stauroptera microstauron..-..-------.--.- 12

Stephanodiscus.- ---__--_-_--_-_--------- 6

subrostrata, Pinnularia------------------- 6,12

Surirellaceae. _ _---____-_---_-_--------- 6

Tabellarioideae.

Valentine Formation,

W

Wagon Bed assemblage.----------_-----_ 6, 7

Wagon Bed Formation____-------_.--- 6

White beds...._.......____1, 2, 3, 4, 5, 7, 8

E17

PLATES 1, 2

Contact photographs of the plates in this report are available, at cost, from U.S. Geological Survey Library, Federal Center, Denver, Colorado 80225.
PLATE 1

FIGURE 1, 2. Melosira italica (Ehrenberg) Kiitzing, X 960, (p. E8).

1. USGS diatom cat. No. 3702-25. Diameter, 15 M2. USGS diatom cat. No. 3702-20. Diameter, 11 M. 

3, 4. Fragilaria brevistriata Grunow, X 960, (p. E9).

3. USGS diatom cat. No. 3737-37. Length, 15 M.

4. USGS diatom cat. No. 3737-38. Length, 15 M. 

5, 6. Fragilaria brevistriata var. inflata (Pantocsek) Hustedt, X 960, (p. E9).

5. USGS diatom cat. No. 3737-39. Length, 12 M .

6. USGS diatom cat. No. 3702-42. Length, 16 M7. Eunotia sp. X 960, (p. E9). USGS diatom cat. No. 3704-19. Length, 29 M. 

8, 9. Cocconeis placentula Ehrenberg, X 960, (p. E9).

8. USGS diatom cat. No. 3704-12. Length, 27 ju9. USGS diatom cat. No. 3700-1. Length, 24 M . 

10, 11. Achnanthes cincta Andrews, n. sp., X 960, (p. E10).

10. Holotype, USGS diatom cat. No. 3737-35. Length, 21 M . Pseudoraphe valve.

11. Holotype, raphe valve. 

12, 13. Anomoeoneis bicapitata Andrews, n. sp., X 960, (p. E10).

12. Holotype, USGS diatom cat. No. 3704-16. Length, 26 M.

13. Paratype, USGS diatom cat. No. 3704-15. Length, 33 M.

14. Anomoeoneis costata (Kiitzing) Hustedt, X 960, (p. E10). USGS diatom cat. No. 3702-36. Length, 38 

15-17. Navicula netroformis Andrews, n. sp., X 960, (p. E10).

15. Holotype, USGS diatom cat. No. 3702-34. Length, 35 p.

16. Paratype, USGS diatom cat. No. 3703-5. Length, 37 M.

17. Paratype, USGS diatom cat. No. 3737-8. Length, 30 M . 

18, 19. Pinnularia brevicostata Cleve, X 960, (p. Ell).

18. USGS diatom cat. No. 3737-16. Length, 65 M19. USGS diatom cat. No. 3702-24. Length, 45 M20, 21. Pinnularia elliptica Lohman and Andrews, X 475, (p. Ell).

20. USGS diatom cat. No. 3702-16. Length, about 166 M21. USGS diatom cat. No. 3702-29. Length, about 190 p. 

22-24. Pinnularia microstauron (Ehrenberg) Cleve, X 960, (p. E12).

22. USGS diatom cat. No. 3737-31. Length, 35 M.

23. USGS diatom cat. No. 3702-47. Length, 40 M.

24. USGS diatom cat. No. 3737-27. Length, 60 M. 

25-27. Pinnularia fusana Andrews, n. sp., X 960, (p. Ell).

25. Holotype, USGS diatom cat. No. 3737-10. Length, 78 ju.

26. Paratype, USGS diatom cat. No. 3702-31. Length, 68 M.

27. Paratype, USGS diatom cat. No. 3702-4. Length, 87 M.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 683 E PLATE 1

re:

I

11

o 0

MELOSIRA, FRAGILARIA, EUNOTIA, COCCONEIS, ACHNANTHES, ANOMOEONEIS,

NAVICULA, AND PINNULARIA
PLATE 2

FIGURE 1, 2. Pinnularia scapha Lohman and Andrews, X 960, (p. E12).

1. USGS diatom cat. No. 3699-18. Length, 48 M2. USGS diatom cat. No. 3702-35. Length, 50 M. 

3-5. Pinnularia subrostrata Lohman and Andrews, X 960, (p. E12).

3. USGS diatom cat. No. 3699-19. Length, 54 M.

4. USGS diatom cat. No. 3737-11. Length, 60 M.

5. USGS diatom cat. No. 3699-13. Length, 52 M . 

6, 7. Amphora deflecta Andrews, n. sp., X 960, (p. E12).

6. Holotype, USGS diatom cat. No. 3700-9. Length, 34 M.

7. Paratype, USGS diatom cat. No. 3699-20. Length, 26 M8-10. Amphora punctata Andrews, n. sp., X 960, (p. E13).

8. Holotype, USGS diatom cat. No. 3443-7. Length, 48 M9. Paratype, USGS diatom cat. No. 3443-13. Length, 47 M .

10. Paratype, USGS diatom cat. No. 3702-33. Length, 40 M - 

11-13. Cymbella cistula var. maculata (Kutzing) Van Heurck, X 960, (p. E13).

11. USGS diatom cat. No. 3702-5. Length, 49 M.

12. USGS diatom cat. No. 3702-28. Length, 44 M .

13. USGS diatom cat. No. 3704-2. Length, 43 M . 

14, 15. Cymbella lanceolata (Ehrenberg) Brun, X 960, (p. E13).

14. USGS diatom cat. No. 3704-17. Length, 74 M.

15. USGS diatom cat. No. 3702-5. Length, 80 M . 

16-18. Gomphonema affine var. insignis (Gregory) Andrews, X 960, (p. E14).

16. USGS diatom cat. No. 3702-19. Length, 55 M17. USGS diatom cat. No. 3702-39. Length, 52 ju.

18. USGS diatom cat. No. 3702-45. Length, 54 M. 

19-22. Hantzschia recta Andrews, n. sp., X 960, (p. E14).

19. Holotype, USGS diatom cat. No. 3737-28. Length, 83 p.

20. Paratype, USGS diatom cat. No. 3737-17. Length, 72 M.

21. Paratype, USGS diatom cat. No. 3737-23. Length, 80 M- Top valve.

22. Same specimen as figure 21, bottom valve.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 683-E PLATE 2

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PINNULARIA, AMPHORA, CYMBELLA, GOMPHONEMA, AND HANTZSCHIA