Some Jurassic Ammonites 

From Central Saudi Arabia

GEOLOGICAL SURVEY PROFESSIONAL PAPER 643-D

Prepared in cooperation with the Saudi Arabia 

Ministry of Petroleum and Mineral Resources 

and the U.S. National Museum^ under the 

sponsorship of the Kingdom of Saudi Arabia 

and the U.S. Department of State

Some Jurassic Ammonites 

From Central Saudi Arabia

By RALPH W. IMLAY

CONTRIBUTIONS TO PALEONTOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 643-D

Prepared in cooperation with the Saudi Arabia 

Ministry of Petroleum and Mineral Resources 

and the U.S. National Museum, under the 

sponsorship of the Kingdom of Saudi Arabia 

and the U.S. Department of State

Descriptions and illustrations of some 

stratigraphically useful ammonites from 

Saudi Arabia

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HIGKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

Washington, D.C. 20402 - Price 55 cents (paper cover)
CONTENTS

Page

Abstract. _ _________________________________________ Dl

Introduction _ ______________________________________ 1

Biological relationships.____________---_--___-__-_-_- 1

Stratigraphic comments._____________--____-____--_- 3

Faunal sequences and correlations-___________________ 3

Geographic and stratigraphic distribution._____________ 8

Systematic descriptions.------.---------------------- 10

References cited-_-___-__-________--___-__-__--____- 14

Index.____________________________________________ 17

ILLUSTRATIONS

[Plates 1-4 follow index]

PLATE 1. Spiroceras, Normannitest, Dhrumaites, Rollieritesl, and Pachyceras.

2. Erymnoceras, E. (Pachyerymnoceras), and E. (Erymnocerites).

3. Grossouvria and Dhrumaites.

4. Dhrumaites.

Page

FIGURE 1. Generalized geologic map of part of the Northern Tuwayq quadrangle, 

Saudi Arabia, showing the distribution of Jurassic fossil localities 

where collections were made in 1962_____________________________ D2

2. Chart showing stratigraphic distribution of ammonites collected in

central Saudi Arabia in 1962__________________________________ 3

3. Chart showing correlation of some Jurassic ammonite faunas in central

Saudi Arabia.________________________________________________ 5

TABLES

Page

TABLE 1. Ammonite genera and subgenera of Bajocian to Callovian ages in central 

Saudi Arabia, showing biological relationships and relative numbers 

available for this and Arkell's (1952) studies___________-___-__--_ D4

2. Geographic distribution of some Toarcian to Callovian ammonites from

central Saudi Arabia______________-_-_--__--__--_-----_--_--_-- 6

3. Some Jurassic fossil localities in central Saudi Arabia.__________________ 8

HI

CONTRIBUTIONS TO PALEONTOLOGY

SOME JURASSIC AMMONITES FROM CENTRAL SAUDI ARABIA

By EALPH W. IMLAT

ABSTRACT

Jurassic ammonites collected stratigraphically in central 

Saudi Arabia show that the ammonite sequence and the ages 

of the formations as determined by Arkell in 1952 are essentially correct and need modification only for parts of the Dhruma Formation. In particular, the middle Bajocian age of the 

lower part of the Dhrurna Formation is extended upward nearly 

to the Ermoceras beds by an occurrence of Dorsetensia just 

below the Dhibi Member. A late Bajocian age for the upper 

part of the Ertnoceras beds is proved by the association of 

Spiroceras Mfnrcatiim (Quenstedt) with Ermoceras and Tliattir 

bocera-s throughout 5.5 meters of beds just above the Dhibi 

Member.

The Bathonian age of most of the middle part of the Dhruma 

Formation above the Ermoceras beds is upheld by the ammonites present. An early Bathonian age for the lower part of the 

Thambites beds is indicated by stratigraphic position. A middle 

Bathonian age for the upper part of those beds is shown by the 

presence of Clydoniceras, provided that the genus has the same 

range as in Europe. Also, rare occurrences of ThamMtes as high 

as the Micromphalites beds show definitely that Thambites 

ranges up into the middle Bathonian. A middle Bathonian age 

for the overlying Tulites and Micromphalites beds is unquestioned. A late Bathonian age for the Dhrum-aUes beds at the 

top of the middle part of the Dhruma Formation is favored 

stratigraphically but is not proved faunally. Nonetheless, the 

presence of a single specimen of Dhrmnmtes from near the base 

of the Tham-Mtes beds shows that the genus existed early in 

Bathonian time and that the main Dhrumaites beds are logically part of the Bathonian succession.

A Oallovian age for most of the upper part of the Dhrtuna 

Formation is proved by the presence of the middle Callovian 

ammonites Pachyceras and Ermtioceras near the base of the 

upper part and by the identity of several species with ammonites in the basal part of the overlying Tuwayq Mountain Limestone. The early Oallovian is either represented by the lower 11 

meters of the upper Dhruma Formation, or by the underlying 

Dhrummtes beds, or by a disconfonnity.

INTRODUCTION

This study of some Jurassic ammonites from central 

Saudi Arabia is a natural extension of the geologic 

mapping project of the Arabian Peninsula carried out 

by the Arabian-American Oil Co. (Aramco) and the 

U.S. Geological Survey under the joint sponsorship of 

the Kingdom of Saudi Arabia, Ministry of Petroleum

and Mineral Eesources, and the U.S. Department of 

State. It is based mainly on collections made by geologists of the Arabian-American Oil Co. and the U.S. 

National Museum since 1952, when W. J. Arkell described all the available Jurassic ammonite collections 

from central Saudi Arabia and evaluated their age significance in terms of the standard European stages (Arkell, 1952). A new evaluation of the age significance of 

the ammonites at this time is opportune because o^her 

paleontologists are now describing the associated eehinoids and pelecypods, which, although much more 

abundant than the ammonites in Saudi Arabia, are 

generally less useful for regional correlations and age 

determinations. Only those ammonites that were not 

available to W. J. Arkell or that add new biologic or 

stratigraphic data are described herein.

Much of the data presented herein concerning the age 

of the Dhruma Formation is based on fossil collections 

made by the Aramco geologists between 1952 and 1962 

and by geologists of the U.S. National Museum in 1962. 

Many thanks are due to the Aramco geologists, R. W. 

Powers and S. D. Bowers, for the privilege of studying 

their ammonite collections, for furnishing locality data, 

and for preparing a locality map of the fossil collections 

made in 1962 (-fig. 1). The excellent preservation of 

some Arabian Jurassic mollusks and echinoids, submitted to me by the Aramco geologists in 1960, stimulated 

the U.S. National Museum specialists Erie Kauffman 

and Porter Kier to go to Saudi Arabia in 1962; thanks 

are also due to these specialists for furnishing data concerning the fossils collected by them.

BIOLOGICAL RELATIONSHIPS

The systematics of most of the Jurassic Toarcian to 

Callovian ammonites of central Saudi Arabia were discussed in considerable detail by Arkell in 1952 (p. 260, 

261, 266, 272, 273, 278, 279, 282, 286-289, 291, 302-306) 

and were modified slightly by him in 1957 (Arkell and 

others, p. L258, L296). Some of his assignments were 

later modified by Westermann (1965, p. 868-871) who

Dl
D2 CONTRIBUTIONS TO PALEONTOLOGY

46°10

FIGURE 1. Generalized geologic map of part of the Northern Tuwayq quadrangle, Saudi Arabia, showing the Jurassic fossil 

localities where collections were made by P. M. Kier, E. G. Kauffman, R. W. Powers, H. A. McClure, and C. D. Redmond 

in 1962. Prepared by R. W. Powers and S. D. Bowers, Arabian-American Oil Go.
SOME JURASSIC AMMONITES FROM CENTRAL SAUDI ARABIA D3

assigned Ermoceras to the Tliamboceratidae because of 

the characteristics of its sutural pattern and the presence of a ventral groove. For the same reasons, specimens that were identified with Stephanoceras and Tel-ocems by Arkell (1952, p. 270, 271) were assigned to 

Ermoceras by Westermann (1965, p. 871, pi. 101, figs. 

4-6). Furthermore, worn specimens of Normannites? 

sp. from Saudi Arabia that were described by Arkell 

(1952, p. 277) as Normannites cf. N. orbignyi Buckman 

(see pi. 1, figs. 9-12) were considered to be "probably 

stephanoceratid," by Westermann (1965, p. 871). In 

fairness to Arkell, his discussion of Ermoceras (Arkell, 

1952, p. 272) shows that he did not consider the presence 

of a ventral growth to be a family characteristic; he was 

highly uncertain about the family assignment of Ermoceras; and he believed that the Tliamboceratidae arose 

from Ermoceras (Arkell, 1952, p. 305, 306; Arkell and 

others, 1957, p. L290).

The biological composition of the ammonite faunas 

as described by Arkell (1952) and supplemented by 

the present study is summarized in table 1.

STRATIGRAPHIC COMMENTS

The Jurassic formations of central Saudi Arabia have 

been described briefly by Bramkamp and Steineke (in 

Arkell 1952, p. 245-249), by Steineke, Bramkamp, and 

Sander (1958, p. 1303-1308) and in detail by Powers, 

Kamirez, Redmond, and Elberg (1966, p. D39-D66). No 

lithologic or detailed stratigraphic data are repeated 

herein because the latest two papers are readily available and because the present paper deals primarily with 

the f aunal and age relationships of the Dhruma Formation and the adjoining formations, as based on 

ammonites (figs. 2,3).

FAUNAL SEQUENCES AND CORRELATIONS

The ammonite succession and the age determinations 

that were made by Arkell (1952, p. 293-299) for the 

Jurassic formations in central Saudi Arabia have been 

upheld very well by subsequent studies (fig. 3). Still 

unquestioned are his assignments of the Marrat Formation to the lower and middle Toarcian and of the 

lower marly beds of the Tuwayq Mountain Limestone 

to the middle Callovian. His assignment of the Dhruma 

Formation to the middle and upper Bajocian and the 

Bathonian is still valid except for the upper part of the 

formation, which is now dated as middle Callovian on 

the basis of ammonites collected in 1962. Arkell had no 

evidence based on ammonites, and there still is none, for 

the presence of beds of late Toarcian, Aalenian, and 

early Bajocian ages. He likewise found no ammonites 

of early Callovian age, but did not exclude the upper 

part of the Dhruma Formation from being of that age.

An unconformity of possible late Toarcian to er.rly 

Bajocian duration between the Marrat and Dhruma 

Formations is suggested by the absence of ammonites 

of those ages (Arkell, 1952, p. 295-303) and by the fact 

that there are only about 28 meters of beds between the 

ammonite faimules of middle Toarcian and middle 

Bajocian ages (Bramkamp and Steineke, 1952, p. 250, 

265, 295). This suggestion is strengthened by the presence in some places of a sharp lithologic break between 

the formations and in other places by unconformable 

overlap of the Dhruma Formation across the Marrat 

and several older formations (Powers and others, 1966, 

p.D45).

The middle Bajocian to middle Callovian ages now 

assigned to the Dhruma Formation are based not only 

on the ammonites described by Arkell (1952, p. 268- 

292) but on other ammonites found later (table 2).

METERS o-

-

50-

100-

g

Forma

TO 

|

Q

<u a

a

ID

^ 

;g

1

c

g"TO

E

o 

u_

In

TO

Hisyan

Member

Atash

Member

Dhibi

Member

Upper

Middle

Lower

Erymnoceras philbyi (KK9-120.5), E.

} (Erymnocerites) sp. (KK9-119.5), Pachyceras

(KK9-112 to -120), and Grossouvria

<KK9-112and'-117)

 Dhrumaites cardioceratoides (KK9-73)

- Micromphalites (KK9-52)

} Thambites planus (KK9-30 to -40)

} Micmmphalites (KK9-14 to -23) 

Thambites planus (KK9-14)

-> Thambites planus 

)(KK8-23, -27.7. -34, -35 to -38) 

/Dhrumaites sp. (KK8-6)

^Thambites planus (KK7-135.1)

p Spiroceras (KK7 131; KK8 basal, 3),

Thamboceras (KK7-130.5), and Ermoceros

\ (KK7 -130.5, -131, -132.3, -133;KK8-basal, -2)

Ermoceras (KK7-113)

} Dorsetensia (KK6)

-Dorst'tensia(KKl-35)

^ Bouleiceras and Protogrammoceras (KK6-14)

^Protogrammoeeras (KK6-10.5 +K1)

FIGUKE 2. Stratigraphic distribution of ammonites collected by 

P. M. Kier and E. G. Kauffman, U.S. National Museum, and 

R. W. Powers, H. A. McClure, and C. D. Redmond, ArabianAmerican Oil Co., in 1962 in central Saudi Arabia. Field 

locality numbers are given in parentheses. (See fig. 1 and 

table 3 for location and description.)
D4 CONTRIBUTIONS TO PALEONTOLOGY

TABLE 1. Ammonite genera and subgenera of Bajocian to Callovian ages in central Saudi Arabia, showing biological relationships and

relative numbers available for this and Arkell's (1952) studies

Family Subfamily Genus and subgenus

Number of Additional

specimens specimens

available available

to Arkell (1952) for this report

Lytoceratidae___________________ Lytoceratinae_________________ Lytoceras?

Spiroceratidae.________________________________________________ Spiroceras

Hildoceratidae__________________ Bouleiceratinae_______________ B<.

Hildoceratinae________________ HUdaites

Harpoceratinae_______________ Protogrammoceras

?Hammatoceratidae._____________ ?Phymatoceratinae____________ Nejdia

Sonninidae.____________________ _____________________________ Dorsetensia

Stephanoceratidae_____________________________________________ Stephanocerasf

Teloceras? _ _

Normannites

Thamboceratidae___----_----_--.______________________________ Thamboceras

Thambites--

Ermoceras--

Clydoniceratidae._____________________________________________ Clydoniceras

Micron 

(C

Dhrumt 

Tulitidae__--------__-___-___________________________ ________ Tulites

Oppelidae.___________________________________________________ Strungia

Pachyceratidae._______________________________________________ Erymnoceras

P

R

Perisphinctidae__________________ Pseudoperisphinctinae________ G

',eras~ - - - - _ -

 as? ___ _ _- ____

Jlydomphalites),. _._ __.

!_ _ ___ ____ _ - _ -

ft ft

uvria _ ___ _ _ _

66?

19 ___-.

27

24

38

4

2

2 ___.

3

25?

77

5 _._-.

24

23

4

13?

1 ___-.

8?

1

1

1

5

1

3

4

2

1

34

10

18

1

3

1

8

2

1

2

1

2

In particular, studies of the ammonites of the KK 

series, as listed in figure 2, show that the sequence of ammonite faunas, and hence the ages as determined by 

Arkell (1952, p. 293), should be modified slightly as 

shown in figure 3. Thus, Dorsetensia ranges as high as 

near the base of the Dhibi Member (loc. KK6). Ermoceras ranges through the Dhibi Member into the lower 

5.5 meters of the middle Dhrmna Formation and is associated in those 5.5 meters with Thamb&ceras and Spiroceras. Thcwnbites has a range of nearly 90 meters, from 

6.1 meters above the Dhibi Member (loc. KK7-135.1) 

into the middle of beds characterized by Micromphalites (loc. KK9-30 to -40). DJimmaites, although most 

common near the top of the middle Dhruma Formation, 

occurs also only 8.5 meters above the Dhibi Member 

(pi. 3, figs. 6, 7). Lastly, Erymnoceraz and Pachyceras. 

which Arkell (1952, p. 289-292) records only from the 

basal marly beds of the Tuwayq Mountain Limestone, 

are now recorded from much lower beds, in the Atash 

Member of the upper Dhruma Formation.

A middle Bajocian age for the Dhruma Formation 

below the Dhibi Member is based on the presence of 

Dorsetensia, (fig. 2), which in western Europe, as discussed by Arkell (1952, p. 269, 295), occurs only in 

the zones of Otoites sa-uzei and Stephanoceras humphriesi-anum.- More precise correlation of the Dorsetensia-be&ring beds in Saudi Arabia with a particular 

European zone cannot be made, however, because of the 

lack of associated ammonite genera that might be stratigraphically more restricted than Dorsetensia. As those

beds in Saudi Arabia grade upward into beds containing late Bajocian ammonites, they are probably equivalent at least to the Stepha-noceras hutnphriesianmn zone. 

A late Baiocian age for the Ermoceras beds in Saudi j o

Arabia is based on the association of that genus with 

Thamboceras and Spiroceras Mfurca-tum (Quenstedt) 

(pi. 1, figs. 1-6) in the lower 5.5 meters of the middle 

part of the Dhruma Formation (fig. 2, 3) ; on ith association at Sinai, Egypt, with. S. Hfurcatwn (Quenstedt) 

and the ammonite genera Oecotvamtes and Leptosphinctes (Arkell, 1952, p. 296) ; and on its association in 

Algeria with species of Cadoinxtes, LeptospMnctes, and 

Oleistosphmctes that are characteristic of the Strenoceras subfurcatum zone at the base of the upper Bajocain in northwest Europe (Arkell and Lucas, 1953; 

Arkell, 1956, p. 264). Of these ammonites Spiroceras 

bifurcatum (Quenstedt) is characteristic of the lower 

and middle parts of the upper Bajocian (Arkell, 1952, 

p. 296); LeptospJimctes and Clei-stosphmetes are known 

only from the upper Bajocian; and Cadomites, Oecotraustes, and Spitwceras are not known below the upper 

Bajocian. Whether the Ernwceras beds correlate only 

with the lowermost upper Bajocian, as suggested by 

Westermann (1965, p. 871), or with the entire upper 

Bajocian, is still undetermined.

The Ermoceras beds in Saudi Arabia ^ere at first 

dated by Arkell (1952, p. 293-296) as "Early-Upper or 

late Middle Bajocian" because most of the above-cited 

ase c5 evidence was not then known, ? but he later dated the

beds as definitely late Bajocian (Arkell, 1956, p. 300).
SOME JURASSIC AMMONITES FROM CENTRAL SAUDI ARABIA D5

European stages

Jurassic

Oxfordian

Callovian

Bathonian

Bajocian

Toarcian

Stratigraphic units in central 

Saudi Arabia

Tuwayq 

Mountain 

Limestone

Dhruma 

Formation

Marrat 

Formation

Upper part

Lower part

Q. 

Q.

^>

T3 

T3

5

<D 

1

Hisyan 

Member

Atash 

Member

Dhibi 

Member

Upper

Middle

Lower

Characteristic ammonites 

(this report)

Pachyceras, 

i 

Erym noceras (1

'Erymnoceras, 

md 

 'achyerym noceras)

Grossou vria

9

Dhrumaites

Micromphalites 

and Thambites (rare)

Tulites

Thambites 

and Dhrumaites (rare)

Spiroceras \

Ermoceras

Dorsetensia

Nejdia and Hildaites

Bouleiceras and 

Protog ra m moceras

Ammonite faunas 

(from Arkell, 1952)

Erymnoceras

Dhrumaites

Micromphalites

Tulites

Ttia.mbites

Ermoceras

Dorsetensia.

Nejdia

Bouleiceras

Ranges of some ammonites 

in Saudi Arabia

Bouleiceras and Spiroceras spp. 

Tulites Protogrammoceras ' schloenbachi spp. Pachyceras cf. P. 

Dorsetensia I 'i-H spp. 

Micromphalites Erymnoceras philbyi spp. 

fErmoceras ' i~ ----- spp. 

Nejdia cf E. Erymnoceras philbyi spp. . Clydoniceras pseudodiscus Erymnoceras (Pachyerymnoceras) jarryi 1 'cf. E. (P.) 

Thamboceras mirabile 

Erymnoceras (Erymnocerites ) l isp. 

planus Thambites 

nouierues ci. K.lenue 

Dhrumaites cardioceratoides sp. 

H 1 

) 1"\

\Grossouvria sp.

FIGUKE 3. Correlation of some Jurassic ammonite faunas in central Saudi Arabia. Solid lines in right-hand column represent 

ammonite ranges1 established by Arkell (1952) ; dashed lines are ranges established in this report.

His earlier tentative assignment was influenced by the 

presence of a few poorly preserved ammonites that he 

compared (Arkell, 1952, p. 270, 271, 277) with species 

of 8te2)Jia)n>oceras, Teloceras, and Normamrdtes from the 

late middle Bajocian of northwest Europe. Of these, the 

specimens assigned by Arkell to Stephanocems and 

Teloceras were later restudied by Westermann (1965, 

p. 870, 871) and reassigned to Ermoceras. The specimens 

assigned by Arkell to Nonnannites are herein refigured 

(pi. 1, figs. 9-12) to show that their generic identity is 

uncertain. Of course, the presence of these three genera 

with Ermoceras would not be surprising and would not 

be evidence of a middle Bajocian age considering that 

all three have been recorded from beds of late Bajocian 

age at many places (Arkell, 1956, p. 63, 99,122,176, 232, 

263, 264, 483; Imlay, 1962, p. A4; Westermann, 1965, 

p. 871).

An early to middle Bathonian age determination for 

the lower three-fourths of the middle part of the

364-898 O 69 2

Dhruma Formation above the Dhibi Member was made 

by Arkell (1952, p. 297). The lowest beds, characterized 

by Thambites, were considered on the basis of stratigraphic position to be lower Bathonian or transitional 

into the Bajocian (Arkell, 1952, p. 297). The succeeding 

beds, characterized by Tulites and MicrampJialites, were 

referred with confidence to the middle Bathonian on 

the basis of the ranges of those genera in northwest 

Europe (Arkell, 1952, p. 297; 1958, p. 236,237; Torrens, 

1965, p. 52), although Micromphalites had been recorded 

from the lower Bathonian (Arkell, 1952, p. 297; 1958, 

p. 236).

The present studies, based on additional collectiors of 

ammonites, modify these age determinations only 

slightly. First, the basal few meters of the middle 

Dhruma Formation are definitely of late Bajocian age, 

as discussed previously, because they contain Spiroceras 

bi/urcatum (Quenstedt), a species characteristic of the 

European zones of Strenoceras subfwrcatmn and Garan-
D6 CONTRIBUTIONS TO PALEONTOLOGY

TABLE 2. Geographic distribution of some Toarcian 

[Locality descriptions are given in table 3. The geographic distrit ution of the KK

Spiroceras bifurcation (Quenstedt) ___ .

annulatum (Deshayes) _ ...........

Protogrammocerasmadagascariense 

(Thevenin). ..........................

sp.... ..............................

Bouleiceras sp.. ...--- ..................

sp...... ......... ...................

Norm ann He sf sp. ...-.--....-....-..-.--

Thamboceras mirabile Arkell ...-.--.-.--

Thambites planus Arkell ................

cf. T. planus Arkell. _ ........---.

aff. E. inerme H. Douville. ...... ...

(.Telermoceras cf. E. (T) coronatoides 

(H. Douville")... .................

(Clydomphalites) clydocromphalus 

Arkell..... .......................

SP.. __......._. -.__._.. -__.--

(Pachyerymnoceras) cf. E. (P.)jarry 

(R. DouvUlfi)-. ------ ...........

Pachyceras cf. P. schloenbachi (Roman) .

Marrat 

Formation

Lower Upper

Bouleiceras

KK6-10.5+K1

X

i CDM 

M

X

Nejdia

S-1655 Aramco 

X

L-941 Aramco 

X

Dhruma

Lower

Dorsetensia

KK7-35

toM 

W

Dhibi 

Member

Ermoceras

L-933 Aramco 

rH 

tl

S-1058 Aramco 

Middle

Spiroceras

lO

o

E

M

S3 

M

CO

!

M

X

S3

X

KK8-basal

X

00M

M

KK8-3

Thambites

1

CQ

g

1

X

rH

CQ

s

1

X

L-932 Aramco 

X

L-931A Aramco 

X

L-931B Aramco 

X

"5

M 

M

X

KK8-6

....

X

00

M

M

X

00

M 

M

X

KK8-34

X

KK8-35 to38

X

timi,a garcm-tiama (Arkell, 1952, p. 296). Second, the 

genus Thanibites at the top of its range is associated 

with MicrompJiaJites (loc. KK9-30 to -40) above the 

Tulites beds and is therefore, in part, of middle Bathoiiian age. Third, the record of Clydoniceras (Arkell, 

1952, p. 282), a middle to late Bathonian genus (Arkell, 

1951, p. 21; 1952, p. 304) in western Europe, at three 

localities in the upper part of the main range of Thambites below the Tulites beds (1952, p. 293) is good evidence of a middle Bathonian age for that part. On the 

basis of these age determinations, there are only about 

19 meters of beds between the occurrences of Spiroceras 

bifurcatum and Clydo-niceras to account for the lower 

Bathonian and perhaps the uppermost Bajocian.

In considering the age of the Thanibites beds, no mention of Clydoniceras was made by Arkell (1952, p. 297), 

but neither did he question the presence of Clydoniceras

in association with TMmUtes (Arkell, 1952, p. 282). In 

the writer's opinion the specimens assigned to Clydoniceras by Arkell clearly belong to that genus rather than 

to TJmmbites, as shown by the presence of an acute 

unicarinate venter. It appears, therefore, that Arkell 

may have had some reservations about the aqre range of 

Clydoniceras in Arabia. If Clydoniceras arose from the 

late Bajocian Th-amfooceras, as Arkell (If 52, p. 305- 

306) thought most probable, its earliest, forms in Arabia 

might be as old as early Bathonian.

Arkell (1952, p. 293, 298) tentatively assigned a late 

Bathonian age to the DJirumattes beds in the upper 

fourth of the middle Dhruma Formation, on the basis 

that Dhnmiaites greatly resembles the underlying middle Bathonian genus Micromphalites and probably belongs in the same Bathonian family, the Clydoniceratidae. Doubts concerning this relationship were ex-
SOME JURASSIC AMMONITES FROM CENTRAL SAUDI ARABIA D7

to Callovian ammonites from central Saudi Arabia

series is shown in figure 1, and the stratigraphic distribution is shown in figure 2]

Formation

Middle

Tulites Micromphalites

L-921 Aramco 

X

S-1150 Aramco 

X

Tfl

3

M 

M

X

X

X

IO 

IO

1

Oi

M 

M

X 

X

X

X

<o 71

Oi

M 

M

X

X 

X

KK9-18 to19

X

1O?;

M 

H

X

KK9-21

X

9

M 

M

KK9-30 to40

KK9-52

Dhrumaites

L-920 Aramco 

COA

M 

M

X

S-1508 Aramco 

X

Upper

Atash Member Undifferentiated

Tuwayq Mountain 

Limestone (part)

Lower

Erymnoceras and Pachyceras

<M

Oi

M 

M

X

KK9-117

X

X

KK9-119.5

KK9-112 to120

KK9-120.5

X

L-919A Aramco 

X

L-919B Aramco 

....

L-929 Aramco 

X

L-942 Aramco 1

S-] Aramco 

X

CD

S-] Aramco 

"x~

1

S- Aramco 

x"

00

Oi

S- Aramco 

X

t>-

Oi

S- Aramco 

~x~

X

L-916A Aramco 

X

pressed by Westermann (1965, p. 873), but he did not 

suggest a different age assignment. Stratigraphically, 

the DJirumaites beds could be either of late Bathonian 

age, or of late Bathonian to early Callovian age. A late 

Bathonian age is favored, however, by the discovery of 

a specimen of Dhrumaites (pi. 3, figs. 6, 7) at locality 

KK8-6, only 8.5 meters above the top of the Dliibi 

Member at a place where derivation from the higher 

level is unlikely for topographic reasons. As DJim- 

 niaites has been found mainly near the top of the 

sequence that bears its name, verification of a Bathonian 

age for the genus would imply that the early Callovian 

is represented either by a disconformity between the 

middle and upper parts of the Dhruma Formation, or 

by the lower 11 meters of the upper part of the Dhruma 

from which no ammonites have been obtained.

A middle Callovian age for most of the upper part 

of the Dhruma Formation is assured by the presence of 

the ammonites PacJvyceras cf. P. schloenba-cJii (Roman), Erytnnoceras pMlbyi Arkell, E. (Pachyerynwoceras] cf. E. (P.) jarryi (R. Douville), E. (Et*ymnocerites] sp., Rottierites cf. R. tenue (Rollier), and Gross&wviia sp. (figs. 2,3). These ammonites were collected 

from 11 to 21 meters above the base of the upper part 

of the Dhruma, which is 89 meters thick, and in the 

Atash Member which is 25 meters thick. The f aunule 

is virtually the same as that found in 25-40 meters of 

soft argillaceous limestone at the base of the Tuws.yq 

Mountain Limestone, which contains three of the same 

species and corresponds likewise to the Ei^ytwioceras 

coronatuni zone of northwest Europe (Arkell, 1952, p. 

289-291,298).
D8 CONTRIBUTIONS TO PALEONTOLOGY

Other ammonites of middle Callovian age, including 

Erymnoceras plulbyi Arkell (loc. L-919A), E. (Pacliyerym/noceras} cf. E, (P,) jarr-yi (R. Douville) (loc. 

L-919B), and E. cf. E. philbyi Arkell (loc. L-942), 

were collected from the upper part of the Dhruma 

Formation, either near the base of the Tuwayq Mountain Limestone, or near the Tuwayq Mountain escarpment. Presumably these fossils were obtained near the 

top of the formation in the Hisyan Member, or its lateral equivalents, and at an appreciably higher stratigraphic position than those from the Atash Member.

GEOGRAPHIC AND STRATIGRAPHIC DISTRIBUTION

Detailed descriptions of Jurassic fossil localities in 

central Saudi Arabia are given in table 3. The positions 

of the described localities relative to geographic and 

cultural features can be obtained by consulting several 

U.S. Geological Survey Miscellaneous Geologic Investigations Maps (Bramkamp and others, 1956; Bramkamp and Ramirez, 1958; and Bramkamp and others, 

1963). Only those localities in the Aramco S series that 

are referred to in this report or that were not described 

previously by Bramkamp and Steineke (in Arkell, 

1952, p. 252-256) are described herein. The occurrences 

of the fossils by localities are indicated in table 2.

TABLE 3. Some Jurassic fossil localities in central Saudi Arabia

[The approximate positions of the Aramco S series of localities, collected by various 

geologists of the Arabian-American Oil Co. between 1933 and 1952, are shown on 

sketch maps in Bramkamp and Steineke (1952, figs. 1, 2). The Aramco L series 

are from the same general area as the S series, and the positions of the KK series 

are shown herein in figure 1. In the KK series, the figure that follows the hyphen 

indicates meters above the base of the sample section (fig. 1)]

Strati-graphic assignment, description of locality, characteristic ammonites, collector, and 

year of- collection

Tuwayq Mountain Limestone, 18 meters 

above base of cliff. Lat 26°21'32" N., 

long 44°48' E., Wadi Aruma quadrangle, Saudi Arabia. Pachyceras cf. P. 

schloenbachi (Roman). 

Dhruma Formation, upper part, near 

base of Tuwayq Mountain escarpment. Lat 25°41'59.25" N., long 

45°12'27.75" E., Northern Tuwayq 

quadrangle, Saudi Arabia. Erymnoceras 

philbyi Arkell.

Dhruma Formation, upper part, 1 meter 

higher than Aramco L-919A at same 

locality. Erymnoceras (Pachyerymnoceras) cf. E. (P.) jarryi (R. Douvill6).

Aramco L-920____ Dhruma Formation, middle part, from 

gypsiferous shale. Lat 24°52'38.50" 

N., long 43°53'51.50" E., Wadi Aruma 

quadrangle, Saudi Arabia. Thambites 

planus Arkell from Dhrumaites zone of 

Bramkamp and Steineke (in Arkell, 

1952, p. 247).

Aramco L-921______ Dhruma Formation, middle part, from

2.2 meters below top of bench of 

chalky limestone. Lat 24°52'51" N., 

long 45°54'04.50" E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Tulites erymnoides Arkell from the 

Dhrumaites or Micromphalites zone. 

See footnotes at end of table.

Collector's 

field No.

Aramco L-916A 1 .--

Aramco L-919A____

Aramco L-919B____

Aramco L-931A____

Aramco L-931B___.

Aramco L-932.

Aramco L-933.

Aramco L-941.

Aramco L-942.

TABLE 3. Some Jurassic fossil localities in central Saudi 

Arabia Continued

Stratigraphio assignment, description of localCollector's ity, characteristic ammonites, collector, and 

field No. year of collection

Aramco L-929____ Dhruma Formation, probably upper part, 

from scree slopes. Lat 24°55'16" N., 

long 45°59'55" E., Northern Tuwayq 

quadrangle, Saudi Arab; a. Ermynoceras 

philbyi Arkell and Rcllierites cf. R. 

tenue (Rollier).

Dhruma Formation, middle part. Lat 

24°11 / 04" N., long 46°17'31.50" E., 

Northern Tuwayq quadrangle, Saudi 

Arabia. Thambites planus Arkell from 

Thambites zone.

Dhruma Formation, middle part. Lat 

24°11'04" N., long 46°17'31.50" E., 

Northern Tuwayq quadrangle, Saudi 

Arabia. Thambites planus Arkell from 

Thambites zone.

Dhruma Formation, middle part. Lat 

24°12'49" N., long 46°17'05" E., 

Northern Tuwayq qua.drangle, Saudi 

Arabia. Thambites planus Arkell from 

the Thambites zone.

Dhruma Formation, lower part, probably 

below base of the Dhibi Member. Lat 

24°10'45" N., long 46°13'20" E., 

Northern Tuwayq quadrangle, Saudi 

Arabia. Ermoceraa (Telermoceras) cf. E. 

(T.) coronatoides (H. Douvill6).

Marrat Formation, upp^r part, from 

limestone beds above sh".le. Lat 24°10'- 

53" N., long 46°09'27.25" E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Nejdia bramkampi Arkell.

Dhruma Formation at top in chalky beds 

below contact with Tuvayq Mountain 

Limestone. Lat 23°14'32" N., long 

46°35'17" E., Southern Tuwayq quadrangle, Saudi Arabia. Erymnoceras cf. 

E. philbyi Arkell.

Dhruma Formation, lover part, from 

14.6 to 15.6 meters below top of Dhibi 

Member. Lat 23°12.8' N., long 46° 

25.8' E., Southern Tuwr.yq quadrangle, 

Saudi Arabia. Equals locality 61 of 

Bramkamp and Steineke (in Arkell, 

1952, p. 256). Normannitest sp. Collector unknown.

Aramco S-1063_____ Dhruma Formation, middle part, 10 

meters above Dhibi Member and 110.6 

meters above base of formation, gypsiferous light-gray to crer.m-colored finegrained limestone. Lat 23°31'12" N., 

long 46°16'24" E., Southern Tuwayq 

quadrangle, Saudi Arabia. Thambites 

planus Arkell from the Thambites 

planus zone. Collected by E. L. Berg, 

R. P. Myers, W. T. SI art, and R. A. 

Bramkamp, 1945.

Aramco S-1150___ Dhruma Formation, middle part. Lat 

24°48'43" N., long 46°58'36" E., 

Northern Tuwayq qurdrangle, Saudi 

Arabia. Micromphalites cf. M. busqueti 

(de Grossouvre) in the Micromphalites 

zone of Bramkamp ard Steineke (in 

Arkell, 1952, p. 248). Collected by D. 

A. Holm and M. P. Ya.ckel, 1947.

Aramco S-1197_____ Tuwayq Mountain Limestone, 22.4 

meters above base. Lat 25°02.4' N., 

long 45°53.1' E., Northern Tuwayq 

quadrangle, Saudi Arabia. Equals 

locality 32 of Bramkam) and Steineke 

(in Arkell, 1952, p. 254). Erymnoceras 

cf. E. philbyi Arkell and Pachyceras cf. 

P. schloenbachi (Roiran). Collector 

unknown.

Aramco S-1058_
SOME JURASSIC AMMONITES FROM CENTRAL SAUDI ARABIA D9

TABLE 3. Some Jurassic fossil localities in central Saudi 

A ra b ia Continued

StratigrapJiic assignment, description of localCollector's ity, characteristic ammonites, collector, and 

field No. year of collection

Aramco S-1198_ __ Tuwayq Mountain Limestone, 15.6 meters 

above base. Same location as Aramco 

S-1197. Equals locality 31 in Bramkamp and Steineke (in Arkell, 1952, 

p. 254). Erymnoceras philbyi Arkell. 

Collector unknown.

Aramco S-1487_-_ Dhruma Formation, middle part, about 

6 meters above Dhibi Member, on 

south side of Wadi Birk. Lat 23°11'00" 

N.; long 46°26'54" E., Southern Tuwayq 

quadrangle, Saudi Arabia. Thambites 

planus Arkell in Thambites zone. Collected by R. A. Bramkamp and N. J. 

Sander, 1948.

Aramco S-1508_ __ Dhruma Formation, top of middle part, 

5.3 meters of beds, below bench-forming 

brown oolitic unit and 80-^85 meters 

above base of Micromphalites-beaTing 

beds, 5.6 kilometers S. 41° W. of 

Khashm Hisan. Lat 25°02.6' N., long 

45°50' E., Northern Tuwayq quadrangle, Saudi Arabia. Equals locality 29 

of Bramkamp and Steineke (in Arkell, 

1952, p. 254) Dhrumaites cardioceratoides Arkell. Collector unknown.

Aramco S-1607_ __ Tuwayq Mountain Limestone, 60.5-62.5 

meters below top of the lower coralbearing unit. Lat 25°18.6' N., long 

45°45.9' E., Northern Tuwayq quadrangle, Saudi Arabia. Equals locality 

21 of Bramkamp and Steineke (in 

Arkell, 1952, p. 253). Erymnoceras cf. 

E. philbyi Arkell. Collector unknown. 

Aramco S-1611_____ Tuwayq Mountain Limestone, lower part.

Lat 25°02.5' N., long 45°40.4' E., 

Northern Tuwayq quadrangle, Saudi 

Arabia. Equals locality 35 of Bramkamp 

and Steineke (in Arkell, 1952, p. 254). 

Erymnoceras cf. E. philbyi Arkell. 

Collector unknown. 

Aramco S-1655.____ Marrat Formation, about 15-17 meters

below top; from slope covered with 

scree of light-colored limestone. Lat 

24°04'06-54" N., long 46°12'OQ-54" 

E., Northern Tuwayq quadrangle, 

Saudi Arabia. Nejdia bramkampi Arkell. 

Collected by R. B. Carr, M. C. Coffield, 

and R. A. Bramkamp, 1951.

Aramco S-1804___._ Tuwayq Mountain Limestone(?); from 

granular cream-colored chalky limestone containing thin-lensing beds of 

sparsely oolitic limestone, about 5 

kilometers northwest of town of Zilfi. 

Lat 26°21'06" N., long 44°47'13" E., 

Wadi Aruma quadrangle, Saudi Arabia. 

Erymnoceras philbyi Arkell. Collected 

by S. J. Roach and W. M. Furnish, 

1952. 

KK6 2-10.5+ K1

(mixed)__________ Marrat Formation, lower member, about

20 meters above base of member. 

Lat 24°14' N., long 46°06' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Protogrammoceras sp. 

KK6-14___________ Marrat Formation, top of lower member,

23.5 meters above base of formation. 

Lat 24° 14' N., long 46° 06'E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Protogrammoceras madagascariense 

(Thevenin) and Bouleiceras sp. 

See footnotes at end of table.

TABLE 3.- -Some Jurassic fossil localities in central Saudi 

Arabia Continued

Collector's 

field No.

KK6.

KK7-35.

KK7-113.

KK7-130.5.

KK7-131.

KK7-132.3.

KK7-133.

KK7-135.1.

KKS-basal.

KK8-2.

KKB-3.

Stratigraphic assignment, description of locality, characteristic ammonites, collector, and 

year of collection

Dhruma Formation, lower part, upner 

one-third of yellow marl below Dl ;bi 

Member, above measured section 

shown in figure 1. Lat 24° 14' N., 

long 46°7' E., Northern Tuwayq 

quadrangle, Saudi Arabia. Dorsetersia 

sp.

Dhruma Formation, lower part, 94 

meters below top of Dhibi Member 

and 26.8 meters above base of formation. Lat 24° 11' N., long 46° 11' E., 

Northern Tuwayq quadrangle, Saudi 

Arabia. Dorsetensia cf. D. Hostraca 

Buckman.

Dhruma Formation, lower part, 16 

meters below top of Dhibi Member. 

Lat 24°11' N., long 46°11' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Ermoceras cf. E. elegans Douvill6 from 

the Ermoceras zone.

Dhruma Formation, middle part, 1.5 

meters above Dhibi Member. Lat 

24°12' N., long 46°11' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Thamboceras mirabile Arkell and Ermoceras aff. E. mogharense Douvillg 

from the top of the Ermoceras zone.

Dhruma Formation, middle part, 2 

meters above Dhibi Member. Lat 

24°12' N., long 46°11' E., Nortt *>rn 

Tuwayq quadrangle, Saudi Arabia. 

Ermoceras mogharense Douville" and 

Spiroceras annulatum (Deshayes) from 

the top of the Ermoceras zone.

Dhruma Formation, middle part, 3.3 

meters above Dhibi Member. Lat 

24°11' N., long 46°11' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Ermoceras elegans Douvill6, E. aff. E. 

mogharense Douvill6 from the top of 

the Ermoceras zone.

Dhruma Formation, middle part, 4 

meters above Dhibi Member. Lat 

24°11' N., long 46°11' E., Nortl -?rn 

Tuwayq quadrangle, Saudi Arabia. 

Ermoceras sp. from the top of the 

Ermoceras zone.

Dhruma Formation, middle part, 6.1 

meters above Dhibi Member. Lat 

24°11' N., long 46°11' E., NortHrn 

Tuwayq quadrangle, Saudi Arabia. 

Thambites planus Arkell from the base 

of the Thambites zone.

Dhruma Formation, base of middle part 

just above Dhibi Member. Lat 24° 11' 

N., long 46° 17' E., Northern Tuwayq 

quadrangle, Saudi Arabia. Ermoceras 

sp. and Spiroceras bifurcatum (Quenstedt) from the top of the Ermoceras 

zone.

Dhruma Formation, middle part, 4.5 

meters above Dhibi Member. Lat 

24°11' N., long 46°17' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Ermoceras mogharense Douville from 

the top of the Ermoceras zone.

Dhruma Formation, middle part, 5.5 

meters above Dhibi Member. Lat 

24°11'N., long 46°17' E., Northern 

Tuwayq quadrangle, Saudi Arr.bia. 

Spiroceras bifurcatum (Quenstedt) from 

the top of the Ermoceras zone.
D10 CONTRIBUTIONS TO PALEONTOLOGY

TABLE 3. Some Jurassic fossil localities in central Saudi 

A ra b i a Continued

Collector's 

field No.

KK8-23.

KK8-27.7.

KK8-34.

KK8-35 to 38.

KK9-14.

KK9-15.5.

KK9-16.

KK9-18 to -19.

KK9-20.5.

KK9-21.

Stratigraphic assignment, description of locality, characteristic ammonites, collector, and 

year of collection

Dhruma Formation, middle part, 8.5 

meters above Dhibi Member. Lat 

24° 11' N., long 46° 17' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Dhrumaites sp. from the Thambites 

zone.

Dhruma Formation, middle part, 25.5 

meters above Dhibi Member. Lat 

24°11' N., long 46°17' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Thambites planus Arkell from the 

Thambites zone.

Dhruma Formation, middle part, 30.2 

meters above Dhibi Member. Lat 

24°11' N., long 46°17' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Thambites planus Arkell from the 

Thambites zone.

Dhruma Formation, middle part, 36.5 

meters above Dhibi Member. Lat 

24°11' N., long 46°17' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Thambites planus Arkell from the 

Thambites zone.

Dhruma Formation, middle part, 37.5- 

40.5 meters above Dhibi Member. 

Lat 24°11' N., long 46°17' E., Northern Tuwayq quadrangle, Saudi Arabia. 

Thambites planus Arkell from the 

Thambites zone.

Dhruma Formation, middle part, 87 

meters below base of Atash Member. 

Lat 24°11' N., long 46°19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Micromphalites sp. and Thambites planus Arkell from the Micromphalites 

zone.

Dhruma Formation, middle part, 85.5 

meters below base of Atash Member. 

Lat 24°11' N., long 46°19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Micromphalites cf. M. busqueti (de 

Grossouvre), M. cf. M. elegans Arkell, 

M. cf. M. pustuliferus (Douville), and 

M. (Clydomaphalites) clydocromphalus 

Arkell from the Micromphalites zone.

Dhruma Formation, middle part, 85 

meters below base of Atash Member. 

Lat 24°11' N., long 46°19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Micromphalites cf. M. busqueti (de 

Grossouvre), M. cf. M. elegans Arkell, 

and M. sp. from the Micromphalites. 

zone.

Dhruma Formation, middle part, 83-84 

meters below base of Atash Member. 

Lat 24° 11' N., long 46° 19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Micromphalites sp. from the Micromphalites zone.

Dhruma Formation, middle part, 80.5 

meters below base of Atash Member. 

Lat 24°11' N.,long 46°19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Micromphalites cf. M. pustuliferus 

(Douville) from the Micromphalites 

zone.

Dhruma Formation, middle part, 80 

meters below base of Atash Member. 

Lat 24° 11' N., long 46° 19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Microtnphalites cf. M. pustiiliferus 

(Douville) and M. sp. juv. from the 

Micromphalites zone.

TABLE 3. Some Jurassic fossil localities in central Saudi 

Arab ia Continued

Collector's 

field No.

KK9-23______-

KK9-30 to 40.

KK9-52.

KK9-73.

KK9-112.

KK9-112 to 120_.._

KK9-117.

Stratigraphic assignment, description of locality, characteristic ammorites, collector, and 

year of collection

Dhruma Formation, middle part 78 

meters below base of Atash Member. 

Lat 24°H'N., Iong46°19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Micromphalites cf. M. elegans Arkell 

from the Micromphalites zone.

Dhruma Formation, middle part, 61-71 

meters below base of Atash Member. 

Lat 24°11' N., long4e°19'E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Thambites planus .Arkell from the 

Micromphalites zone.

Dhruma Formation, middle part, 49 

meters below base of Atash Member. 

Lat 24°12'N., long 46^19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Micromphalites sp. from the Micromphalites zone.

Dhruma Formation, middle part, 28 

meters below base of Atash Member. 

Lat 24° 12' N., long 46° 19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Dhrumaites cardioceratoides Arkell 

from the Dhrumaites z one.

Dhruma Formation, upper part, 11 

meters above base of Atash Member. 

Lat 24°12' N., Iong46°19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Grossouvria sp.

Dhruma Formation, upper part, 11-19 

meters above base of Atash Member. 

Lat 24°12' N., Iong46°19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Pachyceras cf. P. schlovnbachi (Roman).

Dhruma Formation, upper part, 16 

meters above base of Atash Member. 

Lat 24°12' N., long 46°19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Grossouvria sp. and Lytocerasl sp.

Dhruma Formation, upper part, 18.5 

meters above base of Atash Member. 

Lat 24° 12' N., long 46°19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Erymnoceras (Erymnocerites) sp.

Dhruma Formation, upper part, 19.5 

meters above base of Atash Member. 

Lat 24° 12' N., long 46°19' E., Northern 

Tuwayq quadrangle, Saudi Arabia. 

Erymnoceras philbyi Arkell.

' All Arainco L locality collections were made by N. M. Layne, Jr., and H. A. 

McClure in 1961.

2 All KK locality collections were made by P. M. Kier, E. G. Kauffman, E. W. 

Powers, H. A. McClure, and C. D. Redmond in 1962.

SYSTEMATIC DESCRIPTIONS

Family SFIROCERATIDAE Hyatt, 1900 

Genus SPIROCERAS Quenstedt, 1858

Spiroceras bif urea turn (QuenstecT)

Plate 1, figures 1-6 

For synonymy see Potonie, 1929, p. 230, 235-245.

Three worn internal molds of Spiroceras bear ribbing 

of average coarseness for the species 8. bifurcation 

(Quenstedt, 1858, pi. 55, figs. 1-12; 1886, pi. 70, figs. 

27-44; Roman and Petouraud, 1927, pi. 3, figs. 13-20;

KK9-119.5.

KK9-120.5.
SOME JURASSIC AMMONITES FROM CENTRAL SAUDI ARABIA Dll

pi. 4, figs. 1-3, pi. 5, figs. 7-11; and Potonie, 1929, pi. 17, 

figs. 4-25, pi. 18, figs. 26-28). All ribs incline slightly 

adorally on the flanks, become stronger ventrally, and 

terminate on the venter in prominent tubercles that 

bound a smooth midventral area. Except on one much 

swollen rib, there are only faint indications of a second 

row of weak tubercules high on the flanks.

Hypotypes. USNM. 163608-163610.

Occurrence. Dhruma Formation, lower 5.5 meters 

of middle part just above Dhibi Member at localities 

KK8-basal and KK8-3.

Spiroceras annulatum (Deshayes) 

Plate 1, figures 7, 8.

For synonymy see Roman and Petouraud, 1927, p. 33; Potonie, 

1929, p. 240.

On the flanks of one internal mold of Spiroceras 

there are fairly fine, closely spaced, adorally inclined 

ribs that become stronger ventrally. All ribs arch forward on the venter and are reduced considerably in 

strength along the midventral line. All ribs are swollen 

on the venter but are not distinctly tuberculate.

This specimen is closely similar to 8. annulatum 

(Deshayes) as illustrated by d'Orbigny (1850, p. 577, 

pi. 225, figs. 1-7) and Roman and Petouraud (1927, p. 

33, pi. 3, fig. 21, pi. 5, figs. 15-19). These authors show 

that the species in its early growth stages bears weak 

ventral tubercles. The presence of weak tubercles on the 

adult growth stages of some specimens is illustrated by 

Potonie (1929, pi. 17, figs. 24, 25), who notes (1929, p. 

241) that on other specimens, ventral tubercles become 

weak during growth. Apparently, 8. mmul-atum is distinguished from S. Mfiarcatum, by having finer and 

denser ribbing and by the venter of the adult growth 

stages becoming nontuberculate or only weakly 

tuberculate.

The specimen illustrated is nearly identical in appearance with two specimens of Spiroceras from Gebel 

Maghara, Sinai, illustrated by H. Douville (1916, pi. 3, 

figs, lla, b, 13a, b) as Ancyloceras tenui d'Orbigny.

Hypotype. 'US'N'M. 163611

Occurrence. Dhruma Formation, from base of middle part, about 2 meters above the Dhibi Member at locality KK7-131 in association with Ermoceras mogharense Douville.

Family STEPHANOCERATIDAE Neumayr, 1875 

Genus NORMANNITES Munier-Chalmas, 1892

Normannites? sp. 

Plate 1, figures 9-12

Two worn internal molds from the Erm.oceras-he.aring beds in the upper part of the lower Dhruma Formation were assigned to Normannites by Arkell (1952, 

p. 277, 295). The whorls are ovate in section, higher 

than wide, and embrace about half of the preceding 

whorls. The primary ribs are fairly strong and divide 

a little below the middle of the flanks into thinner, 

higher secondary ribs that cross the venter transversely. 

A few secondary ribs arise freely on the flanks. On the 

largest specimen the secondary ribs appear to be slightly 

reduced in strength along the midline of the venter. 

Tubercles are not evident on the flanks. Their absence, 

as well as the thinning of ribs on the venter, may be 

due to weathering, but preclude a definite assignment 

to Nomwmnites until better preserved specimens- are 

found.

Figured specimens. USNM132147.

Occurrence. Dhruma Formation, Dhibi Member, 

from 14.6 to 15.6 meters below top, at Aramco locality 

S-1058.

Family CLYDONICERATIDAE Buckman, 1924 

Genus DHRTIMAITES Arkell, 1952

Dhrumaites cardioceratoides Arkell 

Plate 1, figures 13-15; plate 3, figures 5, 8; plate 4

Dhrumaites cardioceratoides Arkell, 1952, Royal Soc. London 

Philos. Trans., ser. B, v. 236, no. 633, p. 288, pi. 25 figs. 

2, 8, text fig. 10 on p. 289.

There are two large septate specimens in the collections, and the one illustrated is much more complete and 

about the same size as the holotype. The species is characterized by an oxycone shell, a lanceolate whorl section, 

nearly smooth outer septate whorls, faint broad gently 

flexuous ribs that disappear adorally, a vertical umbilical wall that rounds rather abruptly into the flanks and 

a narrow umbilicus that widens slightly on the adoral 

half of the largest septate whorl. The body chamber 

is unknown except possibly for the imprint of the umbilical seam on the entire largest septate whorl. This 

imprint occurs constantly at about one-fifth of the 

height of the flank, which shows that the umbilicus does 

not become increasingly eccentric adorally.

The suture line has a broad first lateral saddle, an 

irregular broad flat first lateral lobe and a bifid se-cond 

lateral lobe. The first and second lateral saddles become 

lower and broader during growth and at a whorl height 

of 145 mm are appreciably broader than on the type 

specimens at a comparable height (Arkell, 1952, fig. 10 

on p. 289).

The illustrated specimen at a diameter of 272 mm 

has a whorl height of 145 mm, a whorl thickness of 75 

mm, and an umbilical width of 35 mm. At a diameter 

of 225 mm, the whorl height is 123 mm, the whorl thickness is 56 mm, and the umbilical width is 25 mm.
D12 CONTRIBUTIONS TO PALEONTOLOGY

The specimens from locality KK9-73, as well as one 

from Aramco locality S-1508 (pi. 3, fig. 9), differ from 

the primary types by having broader saddles and by 

losing all trace of ribbing at much smaller diameter. 

These differences may not be of specific importance considering that Dhrumaites belongs to a family noted for 

having highly variable sutures, that the range of variability in Dhnmiaites is not known, and that all known 

specimens are more or less corroded.

Hypotype. USNM 163612.

Occurrence. Dhruma Formation, middle part, 28 

meters below base of Atash Member at locality KK9-73 

(fig. 2, table 3). The specimens of Dhruonaites cardioceratoides described by Arkell (1952, p. 254, 255, 288) 

were all obtained from the upper 34 meters of the middle part of the Dhruma Formation. The holotype was 

obtained at Aramco locality S-1508 in the upper 7 

meters of the middle part of the Dhruma Formation.

Dhrumaites sp. 

Plate 3, figures 6, 7, 9

One small internal mold of Dhmimmtes (pi. 3, figs. 

6,7) is worth recording because it was found (loc. KK8- 

6) only 8.5 meters above the Dhibi Member of the 

Dhmma Formation, or about 126 meters below the 

lowest occurrence of D. ccKrdiocemtoides Arkell. The 

specimen has a lanceolate whorl section, a small umbilicus, a vertical umbilical wall that rounds abruptly 

into the flanks, and lacks ribbing. The suture line, much 

corroded on the lower fourth of the flanks, is characterized by broad saddles and a broad, irregular first lateral 

lobe. The general pattern of the suture line is similar to 

that of D. cardioceraioides Arkell as herein illustrated 

(pi. 4).

The specimen differs from D. card wee ratoides Arkell 

at a comparable size (Arkell, 1952, pi. 25, figs. 2a, b, 

text fig. 10 on p. 289) by being more compressed, by 

lacking ribbing, and by having lower and broader saddles. Its broad first lateral saddle is similar to that on 

a specimen (pi. 3, fig. 9), labeled Dhvummtes sp. by 

Arkell, that was obtained with the holotype of D. 

cardioceratoides Arkell at Aramco locality S-1508. 

Both specimens could be variants of that species.

Figured specimens. USNM 163613, 163614.

Occurrence. Dhruma Formation, near base of middle 

part, 8.5 meters above Dhibi Member at locality KK8-6; 

near top of middle part at Aramco locality S-1508.

The specimen of Dhrumaites at locality KK8-6 was 

collected from a flat on which the highest beds exposed 

are in the lower part of the middle Dhruma Formation. 

The flat is separated by dry gulches (wadis) on the 

north and east from exposures of the upper part of the

middle Dhruma Formation which hitherto have furnished all specimens of Dhnmiaites. Because of these 

gulches and because the top of the KK8 sequence is only 

63.5 meters above the top of the Dhibi Member, it seems 

unlikely that the ammonite at locality K?"8-6 could 

have been derived as float from the upper part of the 

middle Dhruma, or even as high as the bedr characterized by Mwwmphalites.

Family PACHYCERATIDAE Buckman, 1918 

Genus ERYMNOCERAS Hyatt, 1900

Erymnoceras philbyi Arkell 

Plate 2, figures 3-9

Erymnoceras pMlbyi Arkell, 1952, Royal Soc. London Philos. 

Trans., ser. B, v. 236, no. 633, p. 290, pi. 29, figs. 1-3.

Since this species was described by Arkell (1952, p. 

290), five small specimens have been obtained from the 

Tuwayq Mountain Limestone and one small specimen 

from about 19.5 meters above the base of the upper part 

of Dhruma Formation, near the top of the Atash 

Member.

This ammonite from the Dhruma Formation was at 

first identified by the writer with Tulites erymnoides 

Arkell (1952, p. 284, pi. 25, figs. 1, 4), winch species 

was placed by Arkell in Tulites rather than in Erymnoceras for stratigraphic reasons. It differs from T. 

erymnoides, however, by its ribs arching only gently 

forward on the venter instead of being strongly inclined 

forward. Its present identification with E. philbyi 

Arkell is based on close resemblances to small specimens 

of that species as herein illustrated.

These specimens have coronate whorls, acute and 

rather closely spaced umbilical tubercles, and fairly 

broad ribs that become stronger ventrally. Most of the 

ribs arise in pairs from the umbilical tubercles, but a 

few arise by threes, and some are single.

E. phiTbyi Arkell is possibly represented (pi. 2, figs. 

12, 13), also, by one adult (Aramco loc L-9^-2) that resembles the holotype (Arkell, 1952, pi. 29, fig. la) in 

size, whorl shape, and coiling but differs in having 

coarse simple ribs instead of forked ribs on the adoral 

part of the body chamber.

Types. Hypotypes, USNM 163615-163617.

Occurrence. Tuwayq Mountain Limestone at Aramco localities S-1198 and S-1804; Dhruma Formation, 

about 19.5 meters above base of Atash Member at 

locality KK9-120.5; Dhruma Formation, upper part at 

Aramco localities L-919A and L-929. Probably represented also in Tuwayq Mountain Limestone at Aramco 

localities S-1197, S-1607, and S-1611. Possibly present 

near top of Dhruma Formation at Aramco locality 

L-942.
SOME JURASSIC AMMONITES FROM CENTRAL SAUDI ARABIA D13

Submenus ERYMNOCERITES Jeannet, 1951

Erymnoceras (Erymnocerites) sp.

Plate 2, figures 10, 11

One small fragment has a subovate whorl section that 

is a little wider than high. The flanks converge gently 

from the umbilicus to a moderately rounded venter. 

The umbilicus apparently was moderate in width. The 

ribs incline slightly forward on the flanks and cross the 

venter transversely. The primary ribs are short, are 

swollen at the umbilicus, and divide at one-fourth to onethird of the height of the flanks into two or three weaker 

but fairly sharp, secondary ribs. A few secondary ribs 

arise freely at or above the zone of furcation. The secondary ribs become slightly broader ventrally.

This specimen bears ribbing similar to that on the 

smaller whorls of E. (Erymnocerites} l&uthm>dti~Ro\\\ev 

(Jeannet, 1951, p. 122, pis. 41, 42) but has much less 

strongly projected secondary ribs and probably a narrower whorl section. It differs from Erymnoceras philbyi Arkell by being much more compressed and by lacking prominent umbilical turbercles.

Figured specimen.. USNM 163619.

Occurrence. Dhruma Formation, upper part, 18.5 

meters above base of Atash Member at locality KK 9- 

119.5.

Submenus PACHYERYMNOCERAS Breistroffer, 1947

Erymnoceras (Pachyerymnoceras) cf. E. (P.) jarryi (R. Douvill6)

Plate 2, figures 1, 2

cf. PaoJiyceras jarryi R. Douville, 1912, Soc. Geol. France Mem.

45, v. 19, p. 37, pi. 7, figs. 10, lOa. 

cf. Erymnoceras cf. E. jarryi (R. Douville) Arkell, 1952, Royal

Soc. London Philos. Trans., ser. B. v. 236, no. 633, p. 290,

pi. 29, figs. 4a, b.

The species is probably represented by one internal 

mold of which about one-fourth is septate, coronate, 

and only slightly compressed laterally. The nonseptate 

part is considerably crushed laterally and, consequently, 

is retracted appreciably from the next inner septate 

whorl. The mold bears coarse widely spaced ribs that 

on the septate part arise in pairs from prominent umbilical tubercles and arch gently forward on the venter. 

On the nonseptate part the tubercles weaken adorally, 

most ribs arise singly instead of in pairs, and the single 

ribs alternate with ribs that begin freely near the middle 

of the flanks. All ribs become equally strong ventrally 

and arch gently forward on the venter.

This1 specimen differs from the holotype of E. jarryi 

(E. Douville) mainly in being a little smaller. It has

864^898 O 69, '3

comparable coarse ribs that branch in a similar manner 

and, before crushing, was probably as involute.

Figured specimen. USNM 163620.

Occuren.ce. 'Dhruma Formation, upper part, at 

Aramco locality L-919B.

Genus PACHYCERAS Bayle, 1878

Pachyceras cf. P. schloenbachi (Roman)

Plate 1, figures 18-21

cf. Stepheoceras scTiloenbaclii Roman, 1930, Lyon Univ. L?,b.

G6ologie Travaux, pt. 14, mem. 11, p. 173, pi. 13, figs. 6, Ga. 

Pachyceras cf. P. ttcliloenbachi (Roman). Arkell, 1952, Royal

Soc. London Philos. Trans., ser. B, v. 236, no. 633, p. 291,

pi. 30, figs, la, b.

This species is represented in available collections by 

three specimens, of which the largest two resemble the 

specimen figured by Arkell (1952, pi. 30, figs, la, t). 

The large illustrated specimen bears faint primary ribs 

on the lower parts of the flanks and more numerous, 

broad secondary ribs on the upper parts of the flanl*s. 

These secondaries incline slightly forward on the flanks 

and then cross the venter transversely without reduction 

in strength.

The small illustrated specimen has not been compressed. The whorl section is ovate, slightly higher 

than wide. The flanks are flattened and converge gently 

to a moderately narrow venter. The umbilicus is fairly 

narrow. The umbilical wall is vertical below but rounds 

evenly into the flanks. The primary ribs are broad, low 

to faint, and divide at or a little below the middle of 

the flanks. Some secondary ribs arise freely on the 

upper part of the flanks. All secondary ribs are stronger 

than the primary ribs and become higher and broader 

ventrally.

The specimen shown on plate 1, figures 18, 19 at. a 

diameter of 22 mm has a whorl height of 10.5 mm, a 

whorl thickness of 10 mm, and an umbilical width of 

5 mm.

Figured specimens. USNM. 163621, 163622.

Occurrences. Dhruma Formation, from 11 to 19 

meters above base of Atash Member at locality KK9- 

112 to -120; Tuwayq Mountain Limestone at localities 

L-916A and Aramco S-1197.

Genus ROLLIERITES Jeannet, 1951

Rollierites? cf. R. tenue (Rollier)

Plate 1, figures 16, 17

cf. Rollieriles tenue (Rollier). Jeannet, 1951, Beitr, Geolo-sie 

Schweiz Geophysik. Ser., Lf. 13, v. 5, p. 126, pi. 47, figs. 8 9, 

text fig. 299 on p. 127.

One small laterally compressed internal mold appears 

to 'be fairly evolute. Its primary ribs are moderately
D14 CONTRIBUTIONS TO PALEONTOLOGY

strong, are swollen near the umbilicus, and pass into 

pairs of equally strong secondary ribs at about onefourth to one-third of the height of the flanks. Its secondary ribs incline forward to the flanks, arch gently 

forward on the venter, and become stronger ventrally. 

A few secondary ribs are loosely connected with the primary ribs. The adapical end of the mold, which is least 

compressed, has a whorl height of 13 mm and a whorl 

thickness of 10 mm.

The ribbing on this species is similar to that on Rollie rites tenue (Eollier) (Jeannet, 1951, p. 126, pi. 47, 

figs. 8, 9) and on R. ri-chei (Roman) (Jeannet, 1951, p. 

124; Roman, 1930, p. 172, text fig. 3). Its whorl section, 

as preserved, appears to be a little thinner than that of 

those species.

Figured specimen. USNM 163623.

Occurrence. Dhruma Formation at Aramco locality 

L-929.

Family PERISPHINCTIDAE Steinmann, 1890 

Genus GROSSOITVRIA Siemiradzki, 1898

Grossouvria sp. 

Plate 3, figures 1-4

The genus Grossouvria is represented by two fragmentary specimens. One of these is an internal mold and 

the other retains considerable shelly material. Both bear 

strong, moderately spaced, adorally inclined primary 

ribs. These ribs divide above the middle of the flanks 

into pairs of equally strong secondary ribs that recurve 

backward on the upper parts of the flanks and cross the 

venter transversely. Some secondary ribs are loosely connected with the primary ribs. The internal mold shows 

parts of two whorls, has evolute coiling, and bears one 

deep constriction; its whorl section is ovate and slightly 

wider than high, and its ribs are slightly reduced in 

strength along the midline of the venter. The specimen 

that retains some shell bears a lateral lappet and its 

ribs are not reduced in strength on the venter.

This species closely resembles some of the small 

variants of Grossouvria. curvicosta- (Oppel) illustrated 

by Pfaehler-Erath (1938, pi. 1, figs, la, b, 2a, b) in 

size, shape, and ornamentation.

Figured specimens. USNM 163624,163625.

Occurrences. Dliruma Formation, upper part, from 

11 to 16 meters above base of At ash Member at localities 

KK9-112 and -117.

REFERENCES CITED

Arkell, W. J., 1951, Monograph of the English Bathonian ammonites, pt. 1: Palaeontographical Soe. (v. 104), p. 1-46, 

London.

 1952, Jurassic ammonites from Jebel Tuwayq, central 

Arabia: Royal Soc. London Philos. Trans., ser. B, v. 236, 

no. 633, p. 241-313, pis. 15-30.

 1956, Jurassic geology of the world: London, Oliver & 

Boyd, 806 p., 46 pis., 28 tables, 102 figs.

 1958, Monograph of the English Bathonian ammonites,

pt. 8: Palaeontographical Soc. (v. 112), p. ?09-264, London. 

Arkell, W. J., and Lucas, Gabriel, 1953, Decou^erte recente du

genre Ermooercw Douville dans 1'atlas sahsrien occidental;

consequences stratigraphiques et pale^ogeographiques : Acad.

Sci. Oomptes Bendus, p. 2257-2250. 

Arkell, W. J., and others, 1957, Mollusca 4 Cephalopoda, Amrnonoidea, pt. L of Moore, R. C., ed., Treatise on invertebrate

paleontology: New York and Lawrence, Fans., Geol. Soc.

America and Univ. Kansas Press, 490 p. 

Bramkamp, R. A., Gierhart, R. D., Brown, G. F., and Jackson,

R. O., 1956, Geology of the Southern Tuwayq quadrangle,

Kingdom of Saudi Arabia: U.S. Geol. Survey Misc. Geol.

Inv. Map 1-212, scale 1: 500,000. 

Bramkamp, R. A., and Ramirez, L. F., 1958, Geology of the

Northern Tuwayq quadrangle, Kingdom of Saudi Arabia:

U.S. Geol. Survey Misc. Geol. Inv. Map 1-207, scale

1:500,000. 

Bramkamp, R. A., Ramirez, L. F., Brown, G. F., and Pocock,

A. E., 1963, Geologic map of the Wadi Ar Rrnah quadrangle.

Kingdom of Saudi Arabia: U.S. Geol. Survey Misc. Geol.

Inv. Map 1-206, scale 1: 500,000. 

Douville, Henri, 1916, Les terrains secondaires dans le massif

du Moghara a 1'est de Pisthrne de Suez; Paleont.: Acad.

Sci. Paris Me'rn., ser. 2, v. 54, p. 1-184, 21 pis., 50 text figs. 

Douville, Robert, 1912, Etudes sur les Oardioce~atid6s de Dives,

Villers-sur-Mer et quelques autres gisernents: Soc. Geol.

France Mem. 45, v. 19, 77 p., 5 pis. 

Imlay, R. W., 1962, Late Bajocian ammonite? from the Cook

Inlet region, Alaska: U.S. Geol. Survey Prof. Paper 418-A,

p. A1-A14, pis. 1-5, 4 text figs. 

Jeannet, Alphonse, 1951, Die Eisen-und ITanganerze der

Schweiz; Stratigraphie und Palaontologie des oolithischen

Eisenerzlagers von Herznach und seiner Umgebung, pt. 1:

Beitr. Geologie Schweiz, Geophysik Ser.. Lf.. 13, v. 5, 240

p., 107 pis. 

Orbigny, Alcide d', 1842-51, Paleontologie Francaise; Terrains

Jurassiques, v. 1, Cephalopoda: Paris, 642 p., 234 pis. [For

details on dates see C. Davies Sherborn, 1899. On the dates

of the "Paleontologie Frangaise" of d'Orbi-my: Geol. Mag..

new ser., v. 6, p. 223-225.] 

Pfaehler-Erath, Irene, 1938, Sur quelques Grovsouvria et Choffatia du Callovien de Chezery (Jura francais) : Schweizer.

Palaeont. Gesell. Abh., v. 60, 29 p., 4 pis. 

Potonie, Robert, 1929, The ammonitischen Nebenformen des

Dogger ( Apsorroceras., Spirocera-s, Parapatoceras) : Preuss.

Geol. Landesanstalt Jahrb., v. 50, p. 216-261, pis. 17-19. 

Powers, R. W., Ramirez, L. F., Redmond, C. D., and Elberg, E.

L., Jr., 1966, Geology of the Arabian Peninsula; Sedimentary geology of Saudi Arabia : U.S. Geol. Survey Prof. Paper

560-D, p. D1-D147, pis. 1-10,14 text figs. 

Quenstedt, F. A. von, 1856-58, Der Jura: TuMngen, p. 1-208,

pis. 1-24 (1856) ; p. 209-842, pis. 25-100 (1858). 

 1883-88, Die Ammoniten des Schwabischen Jura: Stuttgart, E. Schweizerbart, 3 v., 1140 p., 126 pis. 

Roman, Frederic, 1930, Etudes sur le Callovien de la Vallee dn

Rhone; Faune du mineral de fer de a vonlte: Lyon Univ.
SOME JURASSIC AMMONITES FROM CENTRAL SAUDI ARABIA D15

La'b. Geologie Travaux, pt. 14, mem. 11, p. 167-197, pis.

13-21. 

Roman, Frederic, and Petouraud, O., 1927 Etude sur la fauna

du Bajocien superieur du Mont cVOr Lyonnais (Ciret),

Cephalopodes: Lyon Univ. Lab. Geologic Travaux, pt. 11,

mem. 9, p. 5-55, pis. 1-7. 

Steineke, Max, Bramkamp, R. A., and Sander, N. J., 1958, Stratigraphic relations of Arabian Jurassic oil in Weeks, L. G.,

ed., Habitat of oil a symposium: Am. Assoc. Petroleum

Geologists Symposium, Tulsa, Okla., June 1958, [vol.], p. 

1294-1329.

Torrens, H. S., 1965, Revised zonal scheme for the Bathcnian 

stage of Europe: Carpatho-Balkan Geol. Assoc., 7th Gong., 

Sofia, September 1965, Part 2, v. 1, p. 47-55, 2 text fig's.

Westermann, G. E. G., 1965, Septal and sutural patterns in 

evolution and taxonomy of Thamboceratidae and Clydoniceratidae (M. Jurassic Animonitina) : Jour. Paleontology, 

v. 39, no. 5, p. 864-874, pis. 101, 102, 4 text figs.

INDEX

[Italic numbers indicate descriptions and major references]

Page 

Age significance of ammonites from Saudi

Arabia........................... Dl

Ancyloceras tenul. ............................ 11

annulatum, Spiroceras................ 6, 9, 11; pi. 1

Arabian Peninsula mapping project.......... 1

Aramco L Series localities.................... 8

Aramco S series localities..................... 8

Atash Member, Dhruma Formation-----.-... 4,

8,10,12,13,14

Beds bearing Dorsetensia...................... 4

Beds bearing Ermoceras- ..................... 11

Beds bearing Micromphalites------------------ 9

bifurcatum, Spiroceras-...,..-... 4, 5, 6, 9, 10; pi. l 

Biological relationships-..-.-...-.....-...-... 1

Bouleiceras.-.-.-.-.-.---.-.--..-.....-.....-. 4

sp........................................ 6,9

Bouleiceratinae...-..---..---...-.---.-----.-. 4

bramkampi,Nejdia .-.-..................... 6,8,9

busqueti, Micromphalites..... ----------------- 6,8,10

Cadomites..................................... 4

cardioceratoides, Dhrumaites -, 6,9,10, 11; pis. 1,3,4 

Cleistosphinctes........... .................... 4

clydocromphalus, Micromphalites (Clydomphalites)................_......... 6,10

(Clydomphalites) clydocromphalus, Micromphalites.... ...............__.... 6,10

Clydoniceras.................................. 4,6

Clydoniceratidae.-__.........___------ 4,6,11

coronatoides, Ermoceras (Telermoceras)-.....-. 6,8

coronatum, Erymnoceras..-................... 7

curvicosta, Orossouvria......................... 14

DhibiMember.---.-..-.-.-.-,.-_---_. 4,9,10,11,12

Dhruma Formation.--....-. 3,4,8,9,10,11,12,13,14 

age..---........-..-.--..--..--...-----. i

Dhrumaites........................ 4,6,7,8,10,11,12

beds... - - .- . g

cardioceratoides---.-....... 6, 9,10, 11; pis. 1,3, 4

sp.............................. 6, 10, 18; pi. 3

zone.-..-----.-----....................... 8

Dorsetensia................................... 4

liostraca.................................. .6,9

sp...........-..- ..-.____ __._.__ 6,9

Echinoids from Arabia....................... l

elegans, Ermoceras............................ g

Micromphalites. --------------.-._.._-..... 6,10

Ermoceras............................... 3,4,5,9,11

inerme....................................

mogharense.............................. 6,9,

(Telermoceras) coronatoides................ e

sp.- .... ...-..................... 6

zone--.-....-.-----.........-.............

Erymnoceras................................. 4,

coronatum. --.--------..--..............._

zone_.--.-----.---.--..-.--.......-.

jarryi................................ .....

phUbyi.................. 6, 7, 8, 9,10, 12, 13; pi

Erymnoceras Continued Page 

(Erymnocerites)........................... D4

leuthardti---.-.- .--.-.-- .-.....-. 13

sp......................... 6, 7, 10, IS; pi. 2

(Pachyerymnoceras)....................... 4

jarryi...................... 6, 7, 8, IS; pi. 2

Erymnocerites... ------------------------------ 13

erymoides, Tulites............................ 6,8,12

Fauaal sequences and correlations ------------ S

Garantiana garantiana........................ 6

garantiana, Oarantiana....-._-.-.-.-.------.-- 6

Geographic and stratigraphic distribution.... 8

Orossouvria---.--_---.______-__.______..___.__ 4,14

curvicosta ................................. 14

sp..............................6,7,l<U4;pl. 3

Hammatoceratidae. ............

Harpoceratinae..--------._.--..

HUdaitet........................

Hildoceratidae_--------------

Hildoceratinae_..............

Hisyan Member.. -.............

humphriesianum, Stephanoceras.

inerme, Ermoceras. -------------

jarryi, Erymnoceras (Pachyerymnoceras') . 6, 

6, 7, 8, IS; pi. 2

KK series localities.-.

Leptosphinctes................................ 4

liostraca, Dorsetensia__-_.-.___-_____._.__.... 6,9

Lytoceras..................................... 4

sp. ---------- ----- .-------------__.. 6,10

Lytoceratidae....-.-.............-.-._-...... 4

Ly toceratina..-..-.---....-....-.-.-......... 4

madagascariense, Protogrammoceras............ 6,9

Mapping project of the Arabian Peninsula.... 1

Marrat Formation---.---...- ............... 3,8,9

Micromphalites...................... 4,5,6,8,9,10,12

busqueti...... ............................ 6,8,10

elegans.................................... 6,10

pustuliferus....----....................... 6,10

(Clydomphalites) ........................ 4

clydocromphalus..... .---...-...-..-..- 6,10

sp........................................ 6,10

zone..- - -_ __--_ _ 8,10

mirabile, Thamboceras......................... 6,9

mogharense, Ermoceras....................... 6,9,11

Mollusks from Arabia.______________________ 1

Nejdia........................................ 4

bramkampi................................ 6,8,9

Normannites.-.-........................... 3,4,5,11

orbignyi.... .............................. 3

sp............................... 3,6,8, 11; pi. 1

Oecotraustes................................... 4

Page

Oppelidae.. -.--..-.-.------------------------ D4

orbignyi, Normannites ... ...... ... -....-.------ 3

Otoitessauzei... ---------------- ------- - 4

Pachyceras. ............................ --- 4,13

jarryi... ............................... 13

tchloenbachi--- 6,7,8,10,13 pi. 1

Pachyceratidae ---------------------------- 4,12

Pachyerymnoceras.-.-------- --- - --- ---------- 13

(Pachyerymnoceras) jarryi, Erymnoceras .... ... 6,

6, 7, 8, IS pi. 2

Perisphinctidae _ --------------- - --- 4,14

philbyi, Erymnoceras...--.------. 6, 7, 8, 9, 10, If; pi. 2

Phymatoceratinae. -----...------------------- 4

planus, Thambttes. ------------------------ 6,8,9,10

Protogrammoceras. ... ------------------------- 4

madagascariense-.---- ..... _-_-_-_-.-..--- 6,9

sp.. - -- 6,9

Pseudoperisphinctinae .-.. .- - 4

pustuliferus, Micromphalites- ------------------ 6, 10

rlchei, 

ie 

riche

-------- 4,13

-------- 14

6,7,8,13-pl. 1

sauzei, Otoietes.. ..-.-.-------. --------- . - . - 4

schloenbachi, Pachyceras..-.----. 6, 7,8, 10, IS- pi. 1

Sonninidae. ---------------------------------- 4

Spiroceras. .................. ........ .- ... -- 4,10

a«BM?aiMm. ----------------------- 6,9,11; pi. 1

bifurcatum. -. 4, 5, 6, 9, 10, 11; pi. 1

Spiroceratidae. -------------------- -------- 4,10

Stephanoceras.. .-..-.-- -..--..--------- -----3, 4, 5

humphriesianum--- ------------------- *

zone..-.------------------------------ 4

Stephanoceratidae -- ------- --------- 4,11

Stratigraphic and geographic distribution . . . . 8

Stratigraphic comments-.-- ---------------- S

Strenocerassubfurcatum.. .. .- - . 4,5

subfurcatum zone _-_-_. -_.- _-------- 4

subfurcatum, Strenoceras. ..................... 4,5

Systematic descriptions ....... - --- 10

Teloceras. ---.--... --- ------------------------ 3,4,5

( Telermoceras) coronatoides, Ermoceras. .... ... 6, 8

tenue,Rollierites - .............. 6, 7, 8, IS, 14: pi. 1

tenui, Ancyloceras ..........---.....-.-------- 11

Thambites.. ........................... 4,5,6,8,9,10

planus- -------------------------- 6,8,9,10

zone--------------------------------- 8,9,10

Thamboceras... ------------------------------ 4, 6

Thamboceratidae- --------------------------- 3,4

TMZito. ------------------------------------ 4,5,6

erymnoides . ---------------------------- 6, 8, 12

Tulitidae --------------------------- 4

Tuwayq Mountain Limestone- ----- 3, 4, 7, 8, 9 12, 13

D17

PLATES 1-4
PLATE 1

[All figures are natural size unless otherwise indicated on plate]

FIGURES 1-6. Spiroceras bifurcalum (Quenstedt) (p. D10).

1, 2. Ventral and lateral views of hypotype, USNM 163610 from locality

KK8-3. Dhruma Formation, near base of middle part. 

3, 4. Lateral and ventral views of hypotype, USNM 163609 from locality KK8-3. Dhruma Formation, near base of middle part. 

5, 6. Ventral and lateral views of hypotype, USNM 163608 from locality KK8-basal. Dhruma Formation, at base of middle part. 

7, 8. Spiroceras annulatum (Deshayes) (p.D 11).

Lateral and ventral views of hypotype, USNM 163611 from locality

KK7-131. Dhruma Formation, near base of middle part. 

9-12. Normannites? sp. (p. Dll).

Ventral (9, 12) and lateral (10, 11) views of worn specimens, USNM 

132147 from Aramco locality S-1058. Dhruma Formation, near top 

of lower part, in Dhibi Member. 

13-15. Dhrumaites cardioceratoides Arkell (p. Dll).

Suture lines drawn at whorl heights of 66, 88, and 145 mm respectively 

on hypotype USNM 163612 (see pi. 4), from locality KK9-73. Dhruma 

Formation, near top of middle part. 

16, 17. RolUerites"! cf. R. tenue (Rollier) (p. D13).

Ventral and lateral views of specimen, USNM 163623 from Aramco

locality L-929. Dhruma Formation, probably upper part. 

18-21. Pachyceras cf. P. schloenbachi (Roman) (p. D13).

18, 19. Ventral and laterial views of specimen, USNM 163622 from 

locality K9-K112 to -120. Dhruma Formation, upper part, Atash 

Member.

20, 21. Lateral and ventral views of specimen, USNM 163621 from 

Aramco locality L-916A. Tuwayq Mountain Limestone, near base.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 643-D PLATE 1

SPIROCERAS, NORMANNITES1, DHRUMAITES, ROLLIERITES 1, AND PACHYCERAS
PLATE 2

[All figures are natural size]

FIGURES 1, 2. Erymnoceras (Pachyerymnoceras) of. E. (P.) jarryi (R. Douvillg) (p. D13). 

Ventral and lateral views of specimen, USNM 163620 from Aramco

locality L-919B. Dhruma Formation, near top of upper part. 

3-9. Erymnoceras philbyi Arkell (p. D12)

3-5. Lateral, ventral, and apertural views of hypotype, USNM 163616 

from Aramco locality L-919A. Dhruma Formation, near top of upper 

part. 

6, 7. Lateral and ventral views of hypotype, USNM 163617 from Aramco

locality L-929. Dhruma Formation, probably upper part. 

8, 9. Ventral and lateral views of hypotype, USNM 163615 from locality

KK9-120.5. Dhruma Formation, upper part, Atash Member. 

10, 11. Erymnoceras (Erymnocerites) sp. (p. D13).

Ventral and lateral views of specimen, USNM 163619 from locality

KK9-119.5. Dhruma Formation, upper part, Atash Member. 

12, 13. Erymnoceras cf. E. philbyi Arkell (p. D12).

Lateral and ventral views of adult specimen, USNM 163618 from Aramco 

locality L-942. Dhruma Formation, at top.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 643-D PLATE 2

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13

ERYMNOCERAS, E. (PACHYERYMNOCERAS), AND #. (ERYMNOCERITES)
PLATE 3

[All figures are natural or nearly natural size unless otherwise indicated on plate]

FIGURES 1-4. Grossouvria sp. (p. D14).

1, 2. Ventral and lateral views showing lateral lappet of specimen,

USNM 163625 from locality KK9-117. Dhruma Formation, upper

part, Atash Member. 

3, 4. Lateral and ventral views of septate specimen, USNM 163624 from

locality KK9-112. Dhruma Formation, upper part, Atash Member. 

5, 8. Dhrumailes cardioceraloides Arkell (p. Dll).

5. Adapical end of large septate whorl (see pi. 4) lighted to emphasize

the presence of faint broad flexuous ribs. Hypotype, USNM 163612

from locality KK9-73. Dhruma Formation, near top of middle part. 

8. Cross-section of same large specimen. 

6, 7, 9. Dhrumaites sp. (p. D12).

6, 7. Cross section and suture lines of fragment, USNM 163613 from

locality KK8-6. Dhruma Formation, near base of middle part. 

9. Found with holotype of D. cardioceratoides Arkell but differs by having

broader saddles as in specimen shown herein on plate 4. Specimen,

USNM 163614, from Aramco locality S-1508. Dhruma Formation,

near top of middle part.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 643-D PLATE 3

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GROSSOUVRIA AND DHRUMAITES
PLATE 4

[Figure about three-fourths natural size]

FIGURE 1. Dhrumaites cardioceratoides Arkell (p. Dll).

Lateral view of large septate specimen, hypotype USNM 163612 from locality 

KK9-73. Other figures of same specimen shown on pi. 1, figs. 13-15 and 

pi. 3, figs. 5, 8. Dhruma Formation, near top of middle part.

U. S. GOVERNMENT PRINTING OFFICE : 1970 O - 364-8
GEOLOGICAL SURVEY PROFESSIONAL PAPER 643-D PLATE 4

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