Growth Series of 

Ostracodes from the 

Permian of Texas

GEOLOGICAL SURVEY PROFESSIONAL PAPER 221-C
Growth Series of 

Ostracodes from the 

Permian of Texas

By I. G. SOHN

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949, PAGES 33-43

GEOLOGICAL SURVEY PROFESSIONAL PAPER 221-C

Illustration and description of new genera 

and a study based on growth series.

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1950
UNITED STATES DEPARTMENT OF THE INTERIOR

Oscar. L. Chapman, Secretary

GEOLOGICAL SURVEY

W. E. Wrather, Director

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

Washington 25, D. C. - Price 15 cents (paper cover)
CONTENTS

Page

Abstract____________________________________________________________________________________________________ 33

Introduction ___________________________________________________________________________________________________ 33

Composition and ecologic significance-__--_______..___________________________________..___________----_-._--------- 33

Method of orienting the valves for measurement_____________________________________________________--------_---_- 34

Growth series.__________________________________________________________________________________________________ 34

Death rates___________________________________________________________________________________________________ 34

Description of localities__.____________________________________________________________________________________ 35

Systematic descriptions.________________________________________________________________________________________ 35

Kirkbyidae__._-________________________________________________________________________ 35

Aurikirkbya Sohn, n. gen______________________________________________________________________________ 35

Aurikirkbya wordensis (Hamilton)____________________________________________________________________ 36

Aurikirkbya barbarae Sohn, n. sp_-_________________.._____^_________________-_____-__-_--__-____----_- 36

Aurikirkbya auriformis Sohn, n. sp_________________________________-____-_---_-__--_-__--_----_---__- 37

Miltonellidae_____-_____._____________________ ______________-__-____--______-_____-----__----- 37

Miltonella Sohn, n. gen_________________________________________________________________________________ 37

Miltonella shupei Sohn, n. sp_____________________________________________-__-_--___-__-_---------__- 37

References cited_______________________________________________________________________________________________ 39

ILLUSTRATIONS

PLATES 7-8. Permian ostracodes from Texas_-__________________________________________-_-__-______-_--_-----_-_- 41-43

FIGURE 2. Frequency distribution of Aurikirkbya wordensis ___________________________-_-__---_-_---_-__------------ 34

FIGURE 3. Theoretical percentage of surviving individuals at successive growth stages._______________.__-__----_----_-_ 35

in

GROWTH SERIES OF OSTRACODES FROM THE MIDDLE PERMIAN

By I. G. SOHN

ABSTRACT

Two new genera of ostracodes, Aurikirkbya and Miltonella, 

from the Permian of the Glass Mountains of Texas are described, and a new family, Miltonellidae, is established. The 

species A. wordensis (Hamilton), previously described, is redefined, and two associated new species, A. barbarae and A. auriformis, are established on the basis of growth series. The new 

species, Miltonella shupei, is described and illustrated by a 

series of valves of increasing size.

Measurements of 252 specimens of A. wordensis (Hamilton) 

are recorded. A graph showing the frequency distribution of 

hinge length of this species is compared with a theoretical graph 

calculated with death rates of 10, 25, and 50 percent to show the 

percent of surviving individuals expected at successive growth 

stages. The fossils under consideration probably do not represent a fraction proportional to the total number of individuals 

that were available for preservation at the time when the sediments were deposited.

INTRODUCTION

This is the second paper describing ostracodes from 

the Permian of the Glass Mountains, Texas. The 

first paper was written by Irving B. Hamilton (1942) 

who described thirteen new species from the upper 

part of the Leonard formation or lower part of the 

Word formation containing silicified fossils part of the 

material collected by G. A. Cooper and N. D. Newell 

(U. S. N. M. loc. 703°). The fossils described by 

Hamilton had been leached out of the calcareous matrix 

with dilute hydrochloric acid. Dr. Cooper's activities 

at the U. S. National Museum in breaking down the 

limestone from this locality provided a large amount 

of material, the study of which disclosed the existence 

of a larger and more diverse faunule than previously 

suspected. In addition to the forms described by 

Hamilton, more than a dozen genera containing from 

one to three species each were obtained. This paper 

establishes two new genera, revises one of the previously described species, and adds three new species. 

These forms are described at the present time because 

they were cited to illustrate certain points in my paper 

"Growth stages in fossil ostracodes." (Sohn, 1948,1950.)

Permission to study this material was given by Dr. 

G. A. Cooper. Drs. R. S. Bassler, J. B. Knight, and 

A. R. Loeblich, Jr., of the U. S. National Museum, and 

Prof. H. N. Coryell, of Columbia University, made 

type material available for examination.

8 64168 50

COMPOSITION AND ECOLOGIC SIGNIFICANCE OF THE

FAUNA

The entire faunule was obtained from the basal portion of an outcrop of dark platy limestone not more 

than 3 feet thick and about 15 feet in extent. Most 

of the exposed material was quarried out and removed 

for leaching. 1 The contained faunule consists predominantly of sponges that are associated with brachiopods, gastropods, pelecypods, crinoids, foraminifers, 

bryozoans, and ostracodes. The material that was 

examined for microfossils is that portion of the undissolved residue which passed through a 10-mesh screen 

and was retained on a 100-mesh screen. It consists of 

fragments and very young individuals of the larger 

fossils, crinoid stems, sponge spicules, ostracodes, 

foraminifers, and quartz. The frequency of ostracode 

occurrence is one specimen in about 2,000 grains of 

other material; the foraminifers are relatively rarer. 

Because the material examined represents a relatively 

small though concentrated portion of the sediment, the 

microfossils are relatively rare in occurrence: the large 

number of individuals of some of the species is due to 

the enormous concentration with respect to the original 

mass of the material.

Silicification preserved the finest ornamentation and 

spines, and obscured muscle scar structure except kirkbyan pits. The ostracodes occur mostly as dissociated 

valves, with a very small proportion of complete carapaces. The larger part of the faunule was probably 

benthonic. Some of the ostracodes (pi. 7, fig. 12) and 

foraminifers have incrusting forms attached to them; 

this implies that burial was not rapid. The fact that 

associated brachiopods and mollusks show evidence of 

minor reworking by currents or waves indicates that 

the sea in which the sediments were deposited was 

probably shallow, possibly not more than 500 feet in 

depth. It is not possible to determine from the ostracodes whether the biota was endemic or was washed 

into the place of burial.

Because all the specimens were obtained from one 

locality, representing a vertical interval of not more 

than 3 feet of a mass of growing sponges, the entire 

faunule may be considered as contemporaneous in

1 Dr. G. A. Cooper, oral communication.

33
34 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949

geologic time. Therefore special attention was paid to 

growth series which were found in various degrees of 

completeness for several species.

METHOD OF ORIENTING THE VALVES FOR 

MEASUREMENT

To measure ostracode valves for statistical studies 

or comparison, it is obvious that unless the specimens 

are oriented in exactly the same manner, the measurements are not significant. In order to obtain uniform 

data, the length and height on the contact margin as 

seen on the interior of the valves, and the convexity 

(width of one valve) in a plane perpendicular to the 

plane of the contact margins were measured. Measurements along the contact margins of the inside of the 

ostracode valves have previously been made by Fowler 

(1909, pp. 221-222) and by Cooper (1946, p. 88, footnote). Cooper did not state the method he used in 

orienting the valves in order to measure consistently in 

the same plane; Fowler complained of the difficulty in 

orienting convex valves, and probably used fine threads 

of drawn glass to prop up the specimens. Other workers pose the specimens by using wax or modeling clay 

props.

The valves were attached by the contact margins to 

a standard glass slide. For convenience of measuring 

the convexity, the specimen was oriented so that the 

greatest length was parallel to a long side of the glass 

slide. A small amount of very dilute gum tragacanth 

is adequate to attach the valve. To measure length 

and height the glass slide with the attached specimen 

was inverted and placed on a cardboard slide (Plummer, 

1929, p. 190) so that the specimen hung down into the 

well of the slide. By focusing through the glass, the 

greatest length and height were measured in the same 

plane.

In order to measure the convexity of the valve, the 

glass slide was stood up on one edge and the microscope 

focused on the plane to be measured. To hold the glass 

slide steady and oriented parallel to the line of sight 

while the measurement was taken, the slide was backed 

by a firm support. By taping 20 glass slides with scotch 

tape a supporting block was built that had a square 

cross section. The glass slide with the attached specimen was pressed against,the supporting block and the 

microscope was focused upon it.

This method is applicable to dissociated valves only, 

and usually cannot be used on complete carapaces. It 

has been used to measure the apertures of biserial 

foraminifers, and it may be found useful in measuring 

other microfossils that have at least one flat surface.

GROWTH SERIES

A growth series of Aurikirkbya wordensis (Hamilton) 

of more than 250 single valves was measured by using 

the above method. The specimens ranged in hinge 

length from 0.8 mm. to 1.8 mm., and it is probable that

a number of younger growth stages were not represented.

It was impossible to distinguish between growth 

stages in this series, because this species apparently 

does not have the growth stage features of the soft parts 

reflected on the valves. The appearance of a posterior 

cardinal spine, which is present in specimens having a 

greatest length of 1.2 mm. (hinge length 1.1 mm.), may 

indicate a growth stage at this size.

The graph (fig. 2) shows the frequency distribution 

of hinge length of A. wordensis (Hamilton) based on 

the recorded measurements. It indicates that it is 

not possible to distinguish between growth stages of 

this species on the basis of the length of hinge. Similar 

graphs constructed for height and for convexity indicate that on those graphs also it is not possible to 

distinguish between growth stages. Consideration of 

some of the factors involved indicates that the shape 

of the graph (fig. 2) is different from the expected curve.

LEFT VALVE RIGHT VALVE 

to

20 10 0 

NUMBER OF SPECIMENS

» 20 

NUMBER OF SPECIMENS

FIGUKE 2. Frequency distribution of Aurikirkbya wordensis. 

DEATH RATES

Fowler (1909, p. 309) calculated the death rate of 

Conchoecia magna Claus as 50 percent between growth 

stages on the basis of a study of 1171 specimens. 

Although Fowler's figure may be too high, it indicates 

that there is a definite decrease in the number of 

individuals between ins tars. The youngest ins tar 

should be represented by a larger number of individuals 

than the next instar, which, in turn, should be numerically larger than the following instar, and so on. A 

graph showing the percentage of individuals surviving 

at successive growth stages was constructed for death 

rates of 10, 25, and 50 percent. This graph (fig. 3) 

shows that the number of individuals in a given population decreases as the ostracodes grow to maturity.

Ostracodes molt between growth stages and the 

discarded valves are subject to fossilization. Because 

there are no criteria to distinguish between exuviae
GROWTH SERIES OF OSTRACODES FROM THE PERMIAN OF TEXAS 35

and dead individuals in fossils, the number of molted 

valves at each growth stage should be added to the 

number of dead individuals at each stage. This procedure would increase the number of individuals that 

are available for preservation at each growth stage.

20

20 40 60 80 100

PERCENTAGE SURVIVING

FIGURE 3. Theoretical percentage of surviving individuals at successive growth

The graph showing the frequency distribution of size 

of hinge length of A wordensis (fig. 2), as well as graphs 

constructed for other species from this locality, and 

for ostracodes from Tertiary and Silurian formations, 

do not resemble the theoretical graph (fig. 3).2 The 

reason for this discrepancy may be the fact that the 

assemblages under consideration do not represent a 

fraction that is proportional to the total number of 

individuals that were available for preservation during 

the time when the sediments were deposited.

In addition to the type locality, the undissolved 

residue of a limestone of established upper Leonard 

age was examined for ostracodes (U. S. N. M. loc. 702"). 

The ostracodes found are rare in occurrence, poorly 

preserved, and show beekite ring replacement. 

Although it is not possible to make specific determination, representatives of both genera described in this 

paper are present.

DESCRIPTION OF LOCALITIES

702c. Upper part of Leonard formation of P. B. Bong, 

from knob on south side of road at elbow just

2 Although figure 2 is not a percentage curve and not comparable to figure 3, the 

number of individuals of each valve is so close to 100 as to approximate a percentage

west of south branch of Hess Canyon, 4.5 miles 

by road northeast of Hess gate, 4.2 miles (airline) N. 48° E. of Hess Kanch, Hess Canyon 

quadrangle, Brewster County, Tex. Collected 

by G. A. Cooper, 1945.

703 c . Upper part of Leonard or lower part of Word 

formation, dark, platy limestone. Crest of 

slope on north side of road, about % mile 

southwest of road fork near old Word Ranch, 

17 to 18 miles north northeast of Marathon, 

Hess Canyon quadrangle, Brewster County, 

Tex. Sponge bed. Collected by G. A. Cooper 

and N. E. Newell, 1941, 1945.

SYSTEMATIC DESCRIPTIONS

Superorder OSTKACODA Latreille

Superfamily BEYKICHIACEA Ulrich and Bassler, 1923

Family KIRKBYIDAE Ulrich and Bassler, 1923

Valves straight-hinged, joined by a ridge or teeth on 

one valve fitting into corresponding groove or sockets 

on the other; essentially equal, with the edge of one 

valve fitting into the slightly rabbeted edge of the 

other, one valve thus slightly overlapping the other. 

Surface reticulate, has" several nodes and a subventral 

pit or muscle spot.

The above description is modified from a description 

given by Bassler and Kellett (1934, p. 32) because the 

orientation of some of the genera in this family has 

been reversed, and also because at least one species, 

Aurikirkbya wordensis (Hamilton), belonging to this 

family has been proved to contain individuals that have 

a reversal of overlap and hingement.

Genus AURIKIRKBYA Sohn, n. gen.

Genotype: A. wordensis (Hamilton), 1942.

This genus is oriented so that the widest end is 

posterior, thus making the muscle scar area in the 

anterior half. The hinge consists of a groove on one 

valve and a corresponding ridge on the other. The 

ridged valve bears two well-developed terminal teeth, and 

the opposing or grooved valve has terminal sockets 

that open to the outside. Overlap consists of the 

beveled margin of the grooved valve fitting into a 

rabbeted edge of the opposing or toothed valve. The 

terminal teeth consist of the thickening of the rabbeted 

overlapping portion of the valve at the cardinal angles.

Differs from Kirkbya, in the presence of two welldefined lobes connected ventrally by a ridge.

Aurikirkbya is placed in Kirkbyidae because the 

overlap is typical of the family, and because the place 

of attachment of the adductor muscle, the so-called 

"kirkbyan pit", is well developed. One species, 

A. wordensis (Hamilton), is known to exhibit reversal 

of overlap and hinge structure.

I have examined figures of all the described species of 

Kirkbya, that are listed in Prof. H. N. CoryelTs un-
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949

published index of Ostracoda except K. alpina Guembel, 1878, and K. schrenkii (Keyserling), 1854, and 

have been able to eliminate all but the following American species from the new genus:

K. canyonensis Harlton, 1929, Univ. Tex. Bull. 2901, p.

153, pi. 2, figs. 5a, b. 

K. kellettae Harlton, 1929, Univ. Tex. Bull. 2901, p. 152,

pi. 2, figs. 2a-d (fig. 2e may belong to a different species). 

K. knighti Harlton, 1929, Univ. Tex. Bull. 2901, p. 153,

pi. 2, figs. 4a, b. 

K. moorei Kellett, 1933, Jour. Paleontology, vol. 7, no. 1,

pp. 89-91, pi. 15, fig. 9 (figs. 10 and 11 may belong to a

different species). 

K. wymani Kellett, 1933, Jour. Paleontology, vol. 7, no. 1,

pp. 91, 92, pi. 15, figs. 23-32.

Of the above listed species I would place K. 

canyonensis, K. kellettae and K. wymani in Aurikirkbya. 

The remaining two species cannot be properly assigned 

without examination of better material. 

Habitat: Marine.

Geologic range: Pennsylvanian and Permian. 

Probable ecology: The massive size and flat venter

indicate that this genus probably crawled along some

surface.

Aurikirkbya wordensis (Hamilton), 1942

PI. 7, figs. 1-13

Kirkbya wordensis Hamilton, 1942 (part), Jour. Paleontology, 

vol. 16, no. 6, pp. 713-714, pi. 110, fig. 13.

Hamilton based the description of this species on 

about a dozen specimens that represent individuals 

belonging to two distinct species. The species is here 

redefined and restricted to specimens that have the 

same features as the holotype.

Carapace subrectangular in lateral view; end margins 

rounded, posterior margin more sharply rounded; 

ventral margin varies from straight in adult to somewhat convex in younger individuals. There is a certain 

amount of individual variation in that some of the 

smaller specimens have ventral margins that are 

straighter than those of some of the larger specimens. 

Greatest length is approximately at midheight.

Posterior lobe or shoulder large, projects above 

hinge line, is subtriangular in dorsal outline. The 

posterior slope of this lobe is steep, makes an angle of 

60° or more with the surface of the valve; anterior 

slope of this lobe is more gentle, making an.angle of 

about 30° with the surface of the valve. In lateral view 

this lobe curves down and forward to form a rounded 

ventral ridge that decreases in size anteriorly, and 

trends toward the anterior lobe. The ventral ridge 

varies in height above the lateral surface of the valve; 

in some specimens it is rounded in cross section and low 

in height, while in other specimens it is keeled and high. 

The specimens with a low ventral ridge have the widest 

part of the valve along the posterior lobe, whereas in 

those specimens that have a high ventral ridge, the 

widest part of the valve is in front of the posterior lobe,

along the ridge. The anterior lobe is small, projects 

only slightly above the hinge line, and is separated from 

the ventral ridge by a shallow sulcus. The anterior 

border of this lobe curves subparallel to the anterior margin. The muscle-scar pit is well defined, oval in shape, 

the larger axis of the oval pointing toward the posterior 

cardinal angle*. The pit is located slightly in front of 

midlength, and just below the ventral ridge in young 

instars; it grows larger in more mature individuals and 

impinges on the ventral ridge, causing that ridge to 

become indented upwards. There is no correlation 

between the size of the pit and the size of the valve; 

larger valves may have pits that are smaller than those 

of smaller valves.

The valve surface below the ventral ridge continues 

unbroken to the ventral edge of the valve which consists of the inner flange. The lobes are separated from 

the end margins by two sulci that open dorsally. The 

inner flange is smooth and thin in younger instars, and 

broad and reticulated in older instars. This flange 

masks the ventral margin in lateral view, and is separated from the outer flange by rows of reticulations 

that form a wall perpendicular to the contact margins. 

The outer flange is carinate, lies in a plane parallel to 

the plane of the contact margins, and appears to be 

very narrow along the ventral margin and to broaden 

at the end margins; the width of this flange probably 

varies with individuals and with age. The two flanges 

converge at the cardinal angles. The inner flange of 

larger specimens develops a backward-pointing spine 

that is located below the posterior cardinal angle. 

Overlap slight; reversal of overlap and hinge structure 

present, though not common (pi. 7, figs. 7a, b).

The presence of a posterior cardinal spine in specimens that have a greatest length of 1.2 mm. (hinge 

length, I.i mm.) may indicate a growth stage at this 

size. The graph showing the frequency distribution 

of hinge length (fig. 2) indicates that it is not possible 

to distinguish between growth stages on the basis of 

size alone.

Type locality: U. S. National Museum locality 703°. 

Hypotypes: U. S. National Museum nos. 114494-

114506. 

Measurements: See table pp. 3S-39.3

Aurikirkbya barbarae Sohn, n. sp.

PI. 7, figs. 14-20

Kirkbya wordensis Hamilton, 1942 (part), Jour. Paleontology, 

vol. 16, no. 6, pp. 713-714.

Differs from A. wordensis (Hamilton) in the presence 

of a well-developed ventral ridge below the kirkbyan 

pit, in the shape of the posterior lobe, in an elongate 

anterior lobe, in a very narrow outer flange, and in the 

absence of a posterior cardinal spine in larger specimens.

3 Plate 7, figure 1, is not included in the table because it is of a broken specimen. 

Its measurements, made on a photograph, are: height, 0.38mm.; convexity, 0.27mm
GROWTH SERIES OF OSTRACODES FROM THE PERMIAN OF TEXAS 37

The oval muscle-scar pit has the longer axis subparallel 

to the dorsal margin.

Hamilton (1942) included specimens of this species 

with Kirkbya wordensis, stating that "The ventral ridge 

is suppressed in immature molts, gaining prominence 

with maturity." Growth series of both species indicate 

that in A. barbarae this second ventral ridge is well 

developed in the smallest instar available (hinge length 

0.93 mm.), whereas specimens of A. wordensis that are 

almost twice as large do not have this feature. The 

fact that immature valves show all the characteristics 

of this species indicates that A. barbarae is probably a 

valid species and not a sexual dimorph of A. wordensis. 

Sexual maturity and associated secondary characteristics in ostracodes appear either in the adult stage or in 

one stage prior to the adult. The range in size of 

individuals having the diagnostic features of either 

species is large enough to represent more than two 

growth stages, and it is therefore assumed that the 

smaller individuals in each of the two species are 

immature, and are two or more growth stages removed 

from the adult.

Type locality: U. S. National Museum locality 703°. 

Holotype: U. S. National Museum no. 114513. 

Paratypes: U. S. National Museum nos. 114507-

114512. 

Measurements (as described in text):

Hinge

Holotype, fig. 20-

Paratypes:

fig. 14__.___ 

fig. 15___.__ 

fig. 16 

fig. 17 

fig. 18 

fig. 19- 

(millimeters)

2.07

.93

.98

1. 13

1. 33

1.47

1. 62

Height Convexity

(milli- (millimeters) meters)

1. 09 0. 70

47

47

56

64

69

78

.31 

.33 

.37 

.44 

.49 

.60

This species is named in honor of 

Sheffer of Brooklyn College, New York, 

the auriform appearance of the genus.

Miss Barbara 

who suggested

Aurikirkbya auriformis Sohn, n. sp.

PL 7, Figs. 21, 22

Differs from the previously described species in the 

presence of a well-defined anterior ventral note, in 

shape of posterior lobe, in absence of posterior spine, 

and in lateral outline.

This species has features in common with both species 

previously described; it is, however, quite distinctive 

and easily differentiated from the other two. It 

differs from A. wymani (Kellett) in shape of posterior 

lobe.

Type locality: U. S. National Museum locality 703 c. 

Holotype: U. S. National Museum no. 114514. 

Paratypes: U. S. National Museum no. 114515. 

Measurements (as described in text) :

864168 50 2

Holotype: fig. 21. 

Paratype: fig. 22.

Hinge 

length 

(millimeters)

1. 18

1.05

Height Convexity 

(milli- (millimeters) meters)

0.59 

. 52

0.41 

.38

Family MIITONEIIIDAE Sohn, n. fam

Straight backed, convex ostracodes with a narrow, 

shallow groove that extends backward from the anterior 

cardinal angle and curves around and below the center 

of the valve subconcentric with the free margins.

Genus MIITONEIIA Sohn, n. gen.

Genotype: M. shupei Sohn, n. sp.

Miltonellidae in which the left valve overlaps the 

right along the free margins, and the right valve overlaps the left along the hinge line. The free margins of 

the left valve are rabbeted to receive the beveled edge 

of the right valve. Hinge consists of a groove in the 

right valve and a corresponding flange in the left. The 

flange is a continuation of the valve surface. The 

groove is composed of two elements: a dorsal part that 

is a continuation of the valve surface, and a lower or 

ventral part that consists of an extension of the beveled 

edge of the free margins.

The only other ostracode genus known to me that has 

a similar groove is the Ordovician genus Conchoprimitia 

Oepik (1935, pp. 4-5) (Primitiidae). Miltonella differs 

from Conchoprimitia in lateral outline, hingement, and 

position of the groove.

Habitat: Marine.

Geologic range: Upper part of Leonard and possibly 

lower part of Word.

Probable ecology: The massive size of the valves indicate that members of this genus probably crawled 

along some surface.

This genus is named in honor of Dr. Charles Milton, 

U. S. Geological Survey.

Miltonella shupei Sohn, n. sp. 

PI. 8, figs. 23-39

Carapace large, massive, subelliptical in lateral view. 

Dorsal margin straight. End margins curved, anterior margin larger. The posterior margin has a 

slight break in its curve located in the dorsal third of 

the valve height. Ventral margin straight to slightly 

concave, the degree of concavity varying with individuals. Valves asymmetrical in outline owing to 

hingement and overlap. Greatest height near the 

anterior cardinal angle. This angle is located nearer 

to the front in the left valve than in the right. Greatest 

length at about mid height. The surface of each valve 

is broken by a shallow sulcus located at about midlength. This sulcus extends from the dorsal margin and 

terminates in a subcentral shallow pit. The narrow 

groove curves below the subcentral pit and terminates 

at the break in the arc of the posterior margin. The
38 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949

groove, the upper part of the posterior margin, and the 

dorsal margin form an almost perfect ellipse. The 

free margins are bordered by a row of fine short spines 

and a very narrow groove located directly above the 

spines (pi. 8, figs. 39d, e). Surface of the valves 

apparently granulose. The preservation of this feature varies with individuals. Dorsal outline subelliptical, greatest width in the posterior quarter, the sides 

are indented where the central sulcus breaks the convexity of the valves; anterior end slightly narrower 

than posterior.

A growth series of this species consists of individuals 

that range in greatest length from 0.66 mm. to 2.50 mm. 

This excludes an undetermined number of younger 

growth stages that are not represented in the series. 

It is not possible to distinguish between successive 

instars on the basis of size. In younger individuals 

the difference in size between the end margins is not 

so pronounced as in older specimens. The anterior 

cardinal angle becomes more distinctly angled with 

age, causing younger individuals to be nearly more 

elliptical in lateral outline than more mature individuals. 

Individuals of this species exhibit considerable variation 

in outline. All these variants were placed within one 

species because there are intermediate forms between 

the extreme variants.

Type locality: U. S. National Museum locality 703°. 

Holotype: U. S. National Museum no. 114516. 

Paratypes: U. S. National Museum nos. 114517- 

114532.

Measurements (as described in text):

Paratypes

fig. 39___-.__

fig. 23__---._

fig. 24____.__

fig. 25___---

fig. 26___--_.

fig. 27__-_-_-

fig. 28-._--_-

fig. 29_.-_--.

fig. 30___.-_-

fig. 31 . 

fig. 32 _

fig. 33____.__

fig. 34 

fig. 35_.___-_

fig. 36. ______

fig. 37 

fig. 38.-.----.

Greatest

length

(millimeters)

._.-_ 1.95

..... .67

..... .65

.___- .96

..... .98

.-.-. 1.35

..... 1.38

...__ 1.68

..... 1.76

...-_ 1.99

.__.. 1.90

----- 2.16

..... 2.09

.._._ 2.35

..... 2.38

..... 2.50

. _._ 2. 52

Height

(millimeters)

1.35

.48

.46

. 62

.65

.89

.95'

1. 16

1. 16

1.31

1.24

1.47

1.33

1.57

1.54

1.71

1.85

Convexity

(millimeters)

0. 14

. 18

.26

.24

.37

.32

.42

.42

.45

.48

.59

.51

. 64

.67

.64

.66

This species is named in honor of Mr. N. W. Shupe, 

U. S. Geological Survey, who made the photographs 

for the plates of this report.

Measurements of Aurikirkbya wordensis (Hamilton)

a

5 &§

B

0.804

.823

.833

.853

.882

.902

.927

.931

.931

.980

.980

.980

1.009

1.029

1.029

1.029

1.029

1.046

1.049

1.058

1.058

1.068

1.068

1.078

1.078

1.078

1.078

1.078

1.078

1.078

1.078

1.078

1.078

1.078

1.088

1.107

1.117

1.117

1.127

1.127

1.127

1.127

1.127

1.127

1.127

I?

saM^

0.412

.392

.412

.441

.470

.441

.461

.490

.470

.490

.470

.490

.559

.490

.588

.539

.588

.570

.539

.490

.559

.588

.568

.617

.568

.588

.588

.588

.539

.588

.588

.588

.588

.588

.539

.539

.539

.588

.588

.588

.549

.539

.588

.588

.588

Convexity (mm.)

0.274

.284

.274

.284

.356

.323

.333

.343

.314

.314

.343

.333

.363

.421

.392

.382

.333

.392

.343

.402

.363

.382

.402

.353

 .363

.402

.412

.392

.392

.392

.412

.372

.392

.412

.382

.392

.402

.402

.412

.412

.392

.392

Remarks '

R

L

R, round venter

L

L, fig. 3

L

L, fig. 2

L

L, corroded

R

R

R, corroded

L, broken

R, corroded

R, broken

L

L, corroded

R

L

R, corroded

L

R

L, fig. 5

L

L, posterior lobe

broken

L, corroded

L, elongate

L

L, broken

L, broken

L

L

L

L, broken

L, cracked

L, broken

R

L

R, broken

R

R, corroded

L, broken

L, spine

L, spine

TJ

.!-»

« a WKi .a 

w

1.127

1.127

1.127

1.127

1.156

1.156

1.156

1.156

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.176

1.196

1.200

1.205

1.205

1.205

1.212

ITa 

IS

0.588

.588

.588

.588

.549

.637

.588

.588

.599

.588

.568

.637

.637

.588

.588

.588

.588

.637

.637

.627

.608

.627

.588

.598

.588

.588

.608

.637

.637

.588

.588

.588

.637

.637

.637

.686

.686

.588

.637

.627

.637

.600

.588

.588

.608

.642

Convexity (mm.)

0.412

.412

.402

.402

.402

.412

.412

.412

.402

.392

.392

.382

.412

.412

".412

.392

.451

.461

.451

.451

.451

.451

.412

.392

.441

.441

.441

.441

.441

.412

.470

.470

.451

.392

.431

.500

.441

.461

.392

.402

.431

.402

.402

.421

.452

Remarks 1

L, spine

L, spine '

L, spine

L. broken

L

L, spine

L

L

R

R

R, broken

R, spec, missing

R

R, broken

R, spine, broken

R, broken

R

L

L, spine

L

L, spine

L, spine

L, spine

L, broken

L

L

L, spine

L

L

L, spine

L, corroded

L, spine

L, spine

L, spine

L, corroded

L, cracked

L, spine

L

L, spine

L, spine, broken

R

R, fig. 6

R, spine

L

L, spine

L, fig. 8

^

la 

§S

w

1.215

1.215

1.215

1.215

1.225

1.225

1.225

1.225

1.225

1.225

1.225

1.225

1.225

1.225

1.236

1.245

1.245

1.245

1.254

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.274

1.323

1.323

1.323

 »_ J3^ be cd "5 a

MS

0.598

.598

.637

.608

.617

.588

.686

.637

.657

.637

.637

.637

.686

.608

.594

.686

.608

.637

.588

.637

.686

.637

.637

.637

.637

.637

.637

.686

.686

.637

.637

.686

.686

.637

.666

.637

.686

.686

.686

.706

.686

.686

.686

.637

.686

.588

Convexity (mm.)

0.431

.392

.461

.470

.421

.402

.470

.461

.480

.470

.441

.470

.490

.421

.404

.500

.441

.490

.392

.412

.461

.441

.421

.441

.441

.441

.441

.470

.490

.461

.470

.500

.490

.490

.490

.441

.490

.480

.490

.470

.490

.480

.500

.451

.470

.441

Remarks '

R, corroded

L, spine

L

L

R

R

L, spine 

L, broken

L, spine

L, spine

L, spine

L, spine

L

L, spine

R, fig. 4

L, spine

L, spine

L, cracked

R

R, spine

R, spine

R, spine

R, spine

R, spine

R, spine

R, spine

R, spine

L, spine, broken

L 

L, spine

L, spine, broken

L, spine

L, spine

L, spine

L, spine

L, spine

L

L, spine

L, spine

L, spine

L, spine, broken

L, spine

L

R

R, spine

R, spine

1?

« a 

H

1.323

1.323

1.323

1.323

1.323

1.323

1.323

1.323

1.323

1.323

1.323

1.323

1.323

1.323

1.328

1.323

1.323

1,323

1.323

1.323

1.323

1.323

1.3?3

1.323

1.323

1.323

1.323

1.323

1.323

1.352

1.355

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

IIW-S

0.637

.686

.686

.686

.686

.686

.686

.686

.637

.637

.686

.686

.686

.666

.686

.637

.686

.735

.686

.686

.686

.686

.686

.686

.686

.686

.715

.735

.686

.686

.665

.637

.735

.686

.637

.637

.686

.735

.735

.784

.686

.735

.735

.686

.735

.715

Convexity (mm.)

0.441

.451

.500

.461

.441

.461

.470

.44}

.441

.470

.490

.490

.519

.490

.490

.490

.510

.490

.500

.490

.510

.500

.500

.490

.510

.500

.490

.441

.510

.519

.487

.470

.490

.441

.461

.461

.470

.470

.490

.441

.461

.490

.490

.480

.490

.490

Remarks '

R

R

R, spine

R, spine

R, spine

R, broken

R, spine, broken

R, spine

R, spine

R, spine

R, spine

L, broken

L, spine, broken

L, spine

L, spine

L

L, spine

L, spine

L, spine

L, broken

L, spine

L, spine

L

L, spine, broken

L, spine

L, spine, broken

L, spine, broken

L, spine

L, spine

L, spine

L, fig. 9

R

R, spine

R, spine

R, spine

R, spine

R, spine

R, spine

R

R

R, spine

R, spine

R, spine

R, spine

R, spine

R

See footnote at end of table.
GROWTH SERIES OF OSTRACODES FROM THE PERMIAN OF TEXAS 39

a

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

1.372

J.372

1.372

1.372

1.372

.372

.372

.372

.372

.392

.401

.401

.421

.421

.421

.421

.421

.421

1.421

1.421

1.421

1.421

1.421

S'- §>g gi

0.735

.686

.735

.735

.686

.735

.735

.735

.735

.735

.715

.686

.686

.686

.686

.764

.735

.706

.735

.735

.784

.686

.735

.686

.686

.686

.686

.686

.735

.735

.706

.735

.735

.735

Convexity j (mm.)

0.500

.461

.519

.539

.490

.500

.519

.549

.510

.549

.519

.539

.539

.539

.500

.510

.490

.510

.549

.48+

.519

.510

.480

.490

.490

.490

.510

.500

.519

.500

.490

.529

.470

.500

Remarks'

R, broken

L, fig. 7

L, corroded

L, spine

L, spine

L, spine

L, spine

L, spine

L, broken

L, spine

L, spine

L, spine

L, spine

L, broken

L, corroded

L, spine

L

L, spine

L, broken

L, spine, broken

L, spine

L, spine

R, spine

R, spine

R, corroded

R, spine

R, spine

R, spine, broken

R

R, spine

R, spine, broken,

corroded

R, spine

R

R

Hinge length 

(mm.)

1.421

1.421

1.421

1.431

1.450

1.450

1.470

1.470

1.470

1.470

1.470

1.470

1.470

1.470

1.470

1.470

1.470

1.470

1.470

1.473

1.499

1.519

1.519

1.519

1.519

1.519

1.519

1.519

1.519

1.519

1.568

1.568

1.568

1.617

1.764

'fi 

wS

0.735

.755

.735

.735

.735

.735

.735

.735

.735

.735

.735

.735

.735

.735

.735

.735

.735

.735

.784

.735

.833

.735

.735

.784

.735

.735

.784

.784

.784

.784

.760

.735

.784

.784

.882

Convexity (mm.)

0.549

.539

.568

.510

.559

.560

.500

.490

.490

.470

.500

.510

.490

.510

.519

.519

.500

.461

.568

.500

.578

.529

.519

.519

.510

.539

.539

.568

.559

.490

.570

.568

.539

.559

.637

Remarks l

L, spine, broken

L, spine, broken

L, spine, broken

R, spine

L, spine

L, fig. 11

R, spine

R, spine, broken

R, spine, corroded

R, spine

R

R, spine, corroded

R, spine

R, spine

R

R, spine

R

R, spine

L, spine

R, fig. 10

L, cracked

R, spine

R

R, spine

R, spine

R, spine

R, spine

R

R, spine

R, spine

R, fig. 12

R

R

R, spine

R, fig. 13

' L, left valve; R, right valve.

REFERENCES CITED

Bassler, R. S., and Kellet, Betty, 1934, Bibliographic index of

Paleozoic Ostracoda: Geol. Soc. America, Special Paper 1,

500 pp. 

Cooper, C. L., 1946, Pennsylvanian ostracodes of Illinois: Illinois

Geol. Survey Bull. 70, 177 pp. 

Fowler, G. M., 1909, Biscayan plankton collected during a

cruise of H. M. S. Research, 1900: Linnean Soc. London,

Trans., Zool., 2d ser., vol. 10, pt. 9, pp. 219-338. 

Hamilton, I. B., 1942, Ostracodes from the upper Permian of

Texas: Jour. Paleontology, vol. 16, no. 6, pp. 712-718, pi.

110. 

Sohn, I. G., 1948, Growth stages in fossil ostracodes (abstract):

Geol. Soc. America Bull., vol. 59, p. 1353. 

 1950, Growth stages in fossil ostracodes: Am. Jour.

Sci., vol. 248 (in press). 

Oepik, Armin, 1935, Ostracoda from the lower Ordovician

Megalaspis-limestone of Estonia and Russia: Univ. Tartu,

Pubs, of the Geol. Inst., no. 44, 13 pp. 

Plummer, H. J., 1929, Photographic slide mount for micro-fossils:

Jour. Paleontology, vol. 3, pp. 189-195.

PLATES 7-8
PLATE 7

(All figures approximately X18. In all cases, a is lateral view from the outside, 6 is lateral view from the inside, c is ventral view, d is dorsal view, and « is posterior view]

FIGURES 1-13. Aurikirkbya wordensis (Hamilton). 1, 4, 6, 10, 12, 13, right valves; 2, 3, 5, 7, 8, 9, 11, left valves; la, b, left valve 

exhibiting reversal of overlap and hingement compare with figs. 8 and 12. The tubelike organism on figs. 

12a, d is probably the foraminifer Tolypammina. Hypotypes, U. S. National Museum nos. 114494-114506. 

14-20. Aurikirkbya barbarae Sohn, n. sp. 15, 16, 17, 18, 20, right valves; 14, 19, left valves. The tubelike void along the 

ventral margin of fig. 206 is due to silicification. Holotype, fig. 20, U. S. National Museum no. 114513. Paratypes, figs. 14-19, U. S. National Museum nos. 114507-114512.

21-22. Aurikirkbya auriformis Sohn, n. sp. 21, holotype, right valva, U. S. National Museum no. 114514; 22, paratype, 

left valve, U. S. National Museum no. 114515.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 221 PLATE 7

PERMIAN OSTRACODES FROM TEXAS
PLATE 8

[All figures approximately X12]

FIGURES 23-39. Miltonella shupei Sohn, n, gen., n. sp. Odd numbers left valves, even numbers right valves; a, lateral view from 

the outside; b, lateral view from the inside; d, dorsal view; e, posterior view. 39, Holotype, U. S. National, 

Museum no. 114516. 23-38, Paratypes, U. S. National Museum nos. 114517-114532.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 221 PLATE 8

PERMIAN OSTRACODES FROM TEXAS