PRELIMINARY REPORT ON FOSSIL VERTEBRATES OF THE SAN PEDRO 

VALLEY, ARIZONA, WITH DESCRIPTIOKS OF NEW SPECIES 

OF RODENTIA AND LAGOMORPHA. 

By JAMES w. GIDLEY. 

INTRODUCTION. 

On the initiative of the United States Geological Survey and with th~ cooperation of the 

United States National Museum, I was privile ed during February, March, and . part of 

April, 1921, to collect fossil vertebrates in the 

San Pedro Valley, Ariz., where remains had previously been located by Kirk Bryan, of the 

Geological Survey. The results of this expedition are here published in part. 

The special problem involved was the determination of the age of the sedimentary deposits, 

which up to that time had been termed PleistoGene. Two localities, a,pparently at slightly 

different . horizons, yielded material representing a fauna sufficiently varied and distinctive 

to establish their age as Pliocene. 

The locality first visited is a small area of 

badlands about 3 miles east of the Curtis ranch ' which is on the State road about 14 miles 

northwest of Tombstone and an equal distance 

southeast of Benson by road. The second 

locality is west of the State road about .2 miles 

south of Benson. These two localities are 

about 12 miles apart and on opposite sides of 

the San Pedro Valley. The first locality 

yielded by far the greater bulk of material, 

but the species represented in the collection 

from the second are more numerous. Stratigraphically there seems to be no difference in 

the level of the beds of the two localities and ' structurally they are very similar, yet, so far 

as I am able to determine, they contain. no 

·species in common. Because of this fact as ' 

well as the general character and assemblage 

of the forms represented, I am led to consider 

them as of slightly different age, the beds at 

the Benson locality being apparently the older. 

Most of the mammal material is fragmentary, 

but several good specimens were procured, 

including enough material for the restoration 

of the dermal armor and skeleton of a Glyptotherium and a possible skeletal restoration of 

a mastodon, both from th~ Curtis locality. 

The material from the Benson ·locality .here 

described was all collected at one spot, a fossil 

bone quarry opened up and worl~ed by Kirk 

Bryan and me. Immediately associated material from this quarry includes fragmentary specimens of Hipparion, Pliauchena?, Platygonus, 

and Pliohippus or Hippidium?, together with a 

new species of h?x turtle and eight new species 

·of birds, not all of which are satisfactorily 

definable from the scanty material obtained. 

The greater part of the specimens included 

in these collections have not yet been prepared, 

but those belonging to the orders Rodentia 

and Lagonl.orpha have been cleaned and 

studied, and the new species are here described. 

Those from the Curtis locality were all found · 

during the excavation of one of the mastodon 

skeletons. Immediately associated with them 

were remains of a llama, a canid, a mustilid, 

a small land turtle, an edentate, and two 

species of small birds. 

A tentative list of the orders, families, 

gener!1, and species, so far as they have been 

determined, represented in each locality · is 

given on page 120. 

119 
120 SHORTER CONTRJBUTIONS TO GENERAL GEOLOGY, 1922. 

Preliminary list of fossil vertebrates from the San Pedro Valley, Ariz. 

Number of species. Number of species. 

Benson. Curtis. Benson. Curtis. 

--- ---

MAMMALIA. MAMMALIA-COntinued. 

Pro boscidia: Lagomorpha: 

Elephantidae: Leporidae: 

Of. Dibelodon, probably n. sp. ___ 2 L epus, 3 sp., possibly new ....... 2 1 

Cf.Gompotherium, probably n. sp. 1 Sylvilagus or Brachylagus sp ...... 1 ···-·-· Perissodactyla: · Edentata: 

Equiidae: Glyptodontidae: 

Equus, undet ................ _ ... ................... 2 Glyptotherium, n. sp ............. .. ........... 1 

Pliohippus, undet .............. 1 ................ ------ Hipparion, undet. .............. 1 ................. Total Mammalia .......... 23 22 

Artiodactyla: ------ Camelidae: REPTILIA. 

Lama, n. sp ..................... 1 

Of. Procamelus, undet ........... 1 1 Testudines: 

Of. Pliauchenia, undet .......... 1 1 Testudinidae: 

Tayassuidae: Testudo, 2 sp. undet . ........... 1 1 

Platygonus cf. P. vetus, or n. sp .. 1 ................. Kinosternodae: 

Cervidae: . Kinosternon, new sp ........... 1 / 1 

Odocoileus, n. sp ................ ................. 1 Batrachia: 

MerJtcodus near M. necatus ...... . 1 1 Salientia: 

Of. erycodus, n. sp ............. 1 Ranidae: 

Carnivora: Rana or Bufo, not yet deterCanids, 3 n. sp ..................... 1 2 Inined .................... 1 ............ Felid?, n. sp ........................ 1 ------ Mustilid, sp ......................... 1 1 Total Reptilia ........ 3 2 

Rodentia: ------ Sciuridae: AVES. 

Citellus cochisei, n. sp ............ ................. 1 

Citellus bensoni, n. sp ............ 1 Galliformes: 

Geomyidae: . Odontophoridae: 

Geomys parvidens, n. sp .......... 1 Undeterinined ... , ............. .................... 1 

Geomys minor, n. sp ............ 1 ............. eolinus sp. undet .. ----.-. 0 0 0. 0 0 1 .. ........... Cratogeomys bensoni, n. sp ...... 1 .................. Fainily undet ....................... 1 .. .............. 

Heteromyidae: Anseriformes: 

JJipodomys minor, n. sp .......... 1 ............. Anatidae: 

Muridae: Dendrocygna, n . sp ............... 1 - --...... - Subfainily Cricetinae: Brant a, n. sp .................... 1 - ........... - Peromyscus brachygnathus, Charadriiformes: " 

n. sp .................... 1 .. .............. Scolopacidae: 

P eromyscus minimus, n. sp .. 1 ................ Micropalama, n. sp .............. 1 - .......... - Peromyscus sp .............. 1 .................. Family undet., medium-sized form .. 1 .. ............... 

Eligmodontia arizonae, n. sp. 1 ................. Columbiformes: 

Onychomys pedroensis, n. sp. 1 Fainily undet. A pigeon somewhat 

Onychomys bensoni, n. sp ... 1 smaller than the domestic dove .... ................ 1 

Sigmodon curtisi, n. sp ...... 1 Passeriformes: I 

Sigmodonm~nor, n. sp .. _ ... '1 Fringillidae: 

Sigmodonmedius, n. sp .. _ . . 1 ................... Small sp., undet ............ . ... 1 ------- &ubfainily Neotomeniae: Other passerines represented by 

Neotomafossilis, n. sp ....... 1 .............. scanty material.. ....... •..... . .... 1 1 

Subfamily Microteinae: ------ Neojiber sp ....... 0 •• 0. 0 ••• 0 ................... 1 Total Aves ..... 0 •••••• _ ••••••••• 8 3 I 

The reptilian remains, including at least GEOLOGIC HORIZON AND CLIMATIC CONDITIONS 

two species of turtles, probably new, are INDICATED. 

being described by C. W. Gilmore, and the This preliminary study reveals littie positive 

bird bones are being studied and will be des- evidence regarding the exact geologic horizon 

cribe.d by Alexander Wetmore, of the Biolog- of the beds in San Pedro Valley, beyond what 

ical Survey, Department of Agriculture. The is stated' above. They seem to be clearly 

tentative lists of Reptilia and Aves given Pliocene? and the peculiar mingling of modern 

above are furnished by these gentlemen. and more ancient forms seems to point rather 
FOSSIL VERTEBRATES OF THE SAN PEDRO VALLEY, ARIZONA. 121 

definitely to a late stage of Pliocene time. 

Unfortunately, the material of these collections represents for the most part new species 

that can not be correlated with known faunas 

of other localities where the age of the b~ds 

has been established. However, the species 

are sufficiently numerous and varied to constitute a standard for comparison;' and future 

field work in this region will almost certainly 

bring to light material that will' defini~ely and 

-correctly determine the proper. sequence of 

these deposits. 

The facts that there are here two or three 

species of true horse (Eq_uus) and that the 

rodents are all referable to modern genera, 

some of which are found living in this general 

region, may suggest Pleistocene age. But 

to offset this evidence of a seemingly more 

modern fauna, the mastodons and glyptodonts are of distinctly Pliocene types, and one 

<>f the canids, though modern in skull and 

dental modifications, has the type of humerus 

belonging to the Miocene and Pliocene canids, 

in that the entepicondylar foramen is prominently present. This feature and the pres-

-ence of Hipparion, Pliohippus, and Merycodus, 

together with the fact that the 15 or more 

species of rodents include no living species, 

-constitute rather conclusive evidence of a 

faunal assemblage that is older than Pleistocene. 

This general assemblage of species, including 

:ptoboscidians, camels, horses, glyptodonts, 

and an extinct species of the ocellated turkey 

:related to a group now living only in Central 

.America and southern Mexico, suggests that 

the climate at the time the beds were laid 

down was rather warm and moist, probably 

. :subtropical or even tropical. 

The presence of a true llama, the glyptodont, and a rodent belonging to a genus now 

Jiving only in South America seems to indicate 

an intermingling of forms of South American 

·origin, and the presence in these Pliocene 

deposits of a rodent and camel of definite 

South American living types suggests the 

derivation of their South American relatives 

from North America and favors the suggestion 

of an exchange of faunas· between the two 

.continents which took place somewhere 'near 

this· epoch of geologic time. 

DESCRIPTIONS OF SPECIES. 

Order RODENTIA. 

The order Rodentia is represented in the San 

Pedro Valley by 17 species, 11 of which occur 

at the Benson locality and 6 at the Curtis locality. Of these species, 15 are here described as 

new, and 2 are not certainly determined on the 

scanty material in hand. However, though 

all the species represented seem to be new, each 

is readily referable to one of ten living genera, 

distributed among four families-the Sciuridae, 

Geomyidae, Heteromyidae, and Muridae. The 

species belonging to the Muridae represent three . 

subfamilies-the Cricetinae, N eotomeniae, and 

Microteinae. 

Family SCIURIDAE. 

The family Sciuridae is represented by two· 

new species, both belonging to the genus 

Oitellus. 

Citellus cochisei Gidley, n. sp. 

Plate XXXIV, figures 1, 2. 

Type.-Portion of a right maxillary containing all the cheek teeth (catalog No. 10490, U.S. 

N.at. Mus.). 

Paratype.-Portion of a left lower jaw (catalog No. 10491). 

Locality.-Both are from the Curtis locality, 

in sec. 25, T. 18 S., R. 21 E., and were found in 

exhuming a mastodon skeleton. 

Description.-Length of upper cheek-tooth 

series 10.5 millimeters. Molars relatively wide, 

m1 and m2 one-third wider than long; lophs 

and valleys simple and narrow; both posterior 

transverse lophs of the molars completely 

united with protocone, forming a short, narrow 

valley opening outward and extending inward 

not more than one-half the width of the tooth 

crown, as in Oynomys. The anterior transverse lophs are more depressed and except in 

m3 are much longer than the other lophs, extending inward and upward to disppear in the 

anterior wall of the protocone. P 4 differs 

from the anterior two molars only in being less 

wide and in having_ the anterior loph relatively 

and actually more extended anteriorly. 

In the greater width of tooth crowns, the less 

extent of their median external reentrant valleys, and the relative shortness of the heel of 

the last molar, this species suggests Oynomys, 

' i 
122 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1922'. 

but it differs from species of that genus in the 

much more brachyodont tooth crowns, he 

greater relative depth of the median external 

reentrant valleys, and the incipiency, amounting to almost total absence, of the posterior reentrant valleys so prominent in species of 

Gynomys. The first of these features might be 

considered as a character of degree only, indicating · less advanced specialization, but the 

other two I consider characters that denote 

relationship with the living species of Gitellus 

rather than with those of the genus Gynomys. 

The lower jaw, as indicated by specimen No. 

· 10491, which carries the incisor and the anterior two cheek teeth, is relatively short and 

deep, the incisor narrow and pointed, and the 

cheek teeth relatively wide to a degree cor-

. responding with those of the upper series. 

This species compares in size with G. evermani, 

but it differs from all the living forms in one or 

more of the characters enumerated above. 

Citellus bensoni Gidley, n. sp. 

Plate XXXIV, figures 3, _4. 

Type.-A first or second upper molar of the 

right side and a last upper molar of the left 

side (catalog No. 10531, U.S. Nat. Mus.). 

Paratype.-The cheek-tooth series of a left 

lower jaw (catalog No. 10532, U.S. Nat. Mus.). 

Locality.-Both from the Benson locality. 

Description:-L~ngth of cheek-tooth series 

(estimated . from measurements of the paratype), 10.3 millimeters; upper molar of about 

the same proportion as the corresponding one 

of G. cochisei at the base but much narrower 

at the summit, owing to the greater slope of the 

inner wall of the protocone; the three transverse lophs about equal in length, the posterior 

·one being broken up into two distinct but 

slightly joined cuspules, the inner one of which 

is a rounded cone entirely disconnected from 

the protocone. 

An upper m3 which I associate with the type 

specimen, like that of G. cochisei, has arelatively small heel portion . as compared with 

living species, and in addition there is a welldefined isolated cone-shaped cuspule near the 

center of the posterior basin. 

This species seems to approach 0. beecheyi 

much more closely than any other living species but differs from it in a few apparently 

important particulars. In G. beecheyi the 

crowns of the upper molars are relatively narrower than in the fossil species, being nearly 

as long as wide; the lingual wall of the protocone is less sloping, and the exterior or buccal 

face of this cusp is much more sloping. Other 

differences noted in the living species are the 

generally less broken up condition of the posterior transverse lophs; the somewhat shallower transverse valleys, the posterior one of 

which usually has a small cuspule at its external 

entrance; and the relatively broader and less. 

completely inclosed posterior valley of the last 

upper molar. 

Beyond the fact that the last lower molar,. 

like the upper, is relatively smaller, and the 

valleys and cusps are somewhat more sharply 

defined than in G. beecheyi, there is little to 

distinguish between the lower cheek teeth of 

that species and G. be~soni. 

Family GEOMYIDAE. 

Three new species . referable to two living 

genera of geomids ~re represented in the collection. 

Geomys parvidens Gidley, n. sp. 

Plate XXXIV, figures 5, 6. 

·Type.-The anterior portion of a skull carrying the incisors and all the cheek teeth except 

the first and last of the right side (catalog No. 

10492, U. S. Nat. Mus.). 

Paratype.-Portion of the right lower jaw 

carrying all the teeth except m3 (catalog No. 

10493, U.S. Nat. Mus.). 

Locality.-Both from the Curtis locality. 

Description.-Length of upper cheek-tooth 

series 5.5 millimeters; width across first upper 

molars (measured. to outer borders) 6.7 millimeters; size small, about the same as that of 

Geomys texensis,· rostrum relatively short and 

heavy; incisors with two very unequal grooves, 

the smaller one close to the inner border of the 

crown, the larger one almost exactly bisectingits anterior face, making the outer of the three . 

ridges thus formed slightly but definitely largest; 

the cheek teeth are relatively small . and not 

greatly expanded laterally, m1 and m2 being 

almost evenly elliptical in outline but with the 

outer edges slightly compressed; p4 with anterior lobe decidedly smaller and less laterally 

expanded than the posterior one; m3 as wide 

as long, subtriangular, relatively small. 

Besides being about equal in size to G. texensis, G. parvidens is almost identical with that 
FOSSIL VERTEBRATES OF THE SAN PEDRO VALLEY, ARIZONA. - 123 

species in the character of the incisors, but it 

differs from G. texensis and the other living 

sp~cies of the genus in general in the less lateral 

expansion of the cheek teeth, the shorter and 

deeper rostrum, and the less progressive character of p4 • 

The lower jaw referred to this species is 

relatively short, with prominent masseteric 

ridge and the submental foramina lying almost 

directly under the anterior end of the masseteric 

ridge. The anterior lobe of p4 is relatively 

small and subcircular, with the walls very little 

flattened. 

p4 with outer reentrant angle rather widely 

V-shaped, the inner one forming a distinct U; 

posterior wall of last molar in the type specimen 

with two distinct and two faint parallel longitudinal grooves forming three low but distinct 

closely grouped median longitudinal enamel 

ridges. , 

This species differs from all living species of 

geomids examined in having the area of the 

anterior porti'on of the masseteric ridge more 

depressed and in the position of the anterior 

submental foramen, which is nearly as in the 

two above-described species of Geomys. In 

Geornys minor Gidley, n. sp. living species this foramen is anterior to the 

Plate XXXIV, figures 7, 8. masset~ric ridge and nearly level with it. In 

-the fossil species it is lower and more posterior Type.-Portion of a right lower jaw lacking 

th I t 1 ( t I N 10494 U S N t in position, lying almost directly under the 

e as mo ar ca a og o. , . . a . anterior extremity of the masseteric ridge. 

Mus.)· There is also between the cheek teeth and the Paratype.~A right upper incisor (catalog anterior border of the coronoid process in 0. 

No. 10534, U.S. Nat. Mus.). b · b d' · 1 k d 1 · r;,nson~ a narrow u t 1st1nct y mar e ongi- Locality.-Both from the Benson locality. tudinal fossa. 

Description.-Length of cheek-tooth series This species is referred to Oratogeomys on the 

(estimated) 5.4 millimeters; the jaw is slightly ~vidence of an associated upper incisor of appro- - smaller than _ that of G. parvidens and differs priate size which has the single groove char_ac- frorn.it otherwi(Se in having the anterior masseteric area more depressed, the submental teristic of this genus. 

:foramen slightly farther back in position, the 

cheek t~eth relatively larger, and the anterior 

lobe of p4 more nearly circular in outline; no 

anterior fossa between cheek teeth and coronoid 

process. 

An associated upper incisor tooth is of appropriate size for the species It shows the characteristic grooving of .a true Geomys, and it is 

this fact which has determined the generic 

reference of G. minor. 

Cratogeornys bensoni Gidley, n. sp. 

Plate XXXIV, figures 9-11. 

Type.-A portion of a left lower j,aw carrying 

all teeth (incisors broken) (catalog No. 10495, 

U. S. Nat. Mus.). 

Paratype.-An upper incisor (catalog No. 

10496, U.S. Nat. Mus.). 

Locality.-Benson locality. The species is 

represented by four other pieces of the lower 

jaws from the same locality. . 

Description.-Lengt)l of cheek-tooth series 8 

millimeters (measured at summits of teeth). 

About the- size of the living species Geomys 

brevicepsJ· cheek teeth not greatly compressed; 

Dipodornys minor Gidley, n. sp. 

Plate XXXIV, figure 16 

Type.-A nearly complete right lower jaw 

containing the incisor and the first cheek tooth 

(catalog. No. 10499, U. S. Nat. Mus.)'. 

Locality.--Benson locality. 

Description.-Length of cheek-tooth row, 

measured from extreme borders of the alveoli, 

4.7 millimeters; size and general jaw characters 

about as in the living species Perodipus chapmani, differing only in its more _slender proportions and in the somewhat m'ore reduced 

condition of the coronoid process. The fourth 

lower premolar, the only one of the cheek-teeth 

series present, is a long crowned and anteriorly 

curved tooth which is double-lobed, the anterior lobe having an anterior reentrant angle as 

in P. chapmani, but this tooth differs from the 

tooth of that species in having the posterior 

lobe relatively wider. Also the alveolus of the 

last molar is only about one-half the width of 

that of the other molars, indicating that this 

tooth is relatively more reduced than in the 

living species~ 
124 SHORTER CONTRI~UTIONS TO GENERAL GEOLOGY, 1922. 

Family MURIDAE. 

The family Muridae is rather abundantly 

represented at both localities. The 12 determinable species are distributed among three· 

subfamilies, 10 belonging to the Cricetinae, 1 

. to the Microtinae, and 1 to the N eotomeniae. 

Genus PEROMYSCUS. 

Specimens found at the Benson locality are 

referable to three species of Peromyscu~. Two 

of these are new, although one is apparently 

closely related to the P. taylori group. The 

other new species is more distinctive. The 

third, represented by a single lower jaw lacking the cheek teeth, has not been determined. 

Peromyscus brachygnathus Gidley, n. sp. 

Plate XXXIV, figure 12. 

Type.-The greater portion of a right lower 

jaw c.arrying all the teeth (catalog No. 10501, 

U.S. Nat. Mus.). 

Locality. -Curtis locality. 

Description.-Length of cheek-tooth series, 

2.8 millimeters; about the size of P. tayloriJ· 

jaw relatively short anterior to cheek teeth; 

last molar very much reduced, as. much as in 

any living species of Onychomys. The teeth 

are too much worn to determine accurately 

their normal height in unworn condition, but 

they appear to be of the depressed type of P. 

taylori. 

The form and position of the anterior extension of the masseteric ridge, the general character of the coronoid region, and the relatively 

broadly expanded anterior lobe of the anterior 

cheek tooth seem to determine the generic reference of this species, but it differs from aU 

living species of the genus in the relatively 

short jaw and the greater reduction of the last 

lower cheek tooth, which seems to have nearly 

or quite lost its hinder lobe. 

Peromyscus minimus Gidley, n. sp. 

Plate XXXIV, figt.Ire 13. 

Type.-Portion of a left lower jaw carrying 

all the teeth (catalog No. 10500, U. S. Nat. 

Mus.). 

Locality.-Benson locality. 

Description.-Size very small, length of cheektooth series 2.6 millimeters; cheek-tooth cusps 

depressed, wit):! well-marked cingula at the entrance of the external valley, and with tendency to inclose the internal ones by an uprising of the inner enamel wall between the 

cusps; anterior lobe of the first cheek tooth, 

p4, relatively narrow but two-cusped at the 

summit; posterior lobe of last cheek tooth 

small, almost as much reduced as in Onychomys . 

This species seems more nearly related to 

P. taylori than to any other living species but 

differs from it in having a narrow divided anterior lobe of the first cheek tooth and a more 

reduced hinder molar. It further differs from 

that species and more nearly agrees with others 

of the genus in the wider angle at which the 

coronoid portio'n of the ascending ramus diverges from the alveolar portion of the jaw. 

P. minimus is distinguished from P. brachygnathus in that the jaw is somewhat more 

slender in proportions; the masseteric ridge is 

less advanced forward; the · cheek teeth are 

slightly narrower; the anterior lobe of the first 

cheek tooth is narrow and double cusped, while 

that of P. brachygnathus is wider and undivided, 

and the .last cheek tooth is somewhat less 

reduced. 

Peromyscus sp. 

Plate XXXIV, figure 14. 

A second and larger species, about equaling 

Peromyscus m. gambeli in size, is represented by a 

lower jaw (catalog No. 10502, U.S. Nat. Mus.) 

lacking all the cheek teeth. Length of cheektooth serie~ as estimated by measurement of 

the alveoli, 3.8 millimeters. This jaw, in its 

general form and in the position of the anterior extremity of the masseteric ridge, is 

sufficiently characterized to make certain its 

generic reference, but its specific features can 

not be determined until the cheek teeth are 

known. 

Genus ELIGMODONTIA. 

The genus Eligmodontia, the living species 

of which are confined to the South America 

continent, is represented by a single species in 

the fossil collection from Arizona. 

Eligmodontia arizonae Gidley, n. sp. 

Plate XXXIV, figure 15. 

Type.-Greater porti~n of a left lower jaw 

containing the complete dentition (catalog 

No. 10503, U.S. Nat. Mus.). 

Paratype.-Single lower jaws of two other 

individuals (catalog Nos. 10504, 10505). 

Locality.-All from Benson locality. 
FOSSIL VER,TEBRATES OF THE SAN PEDRO VALLEY, ARIZONA. 125 

Description.-Length of cheek-tooth series 

3.6 millimeters; about the size of. the living 

. species E. morgani, but may be distinguished 

from it by its relatively greater depth of jaws, · 

its decidedly shorter symphysis, and , the less 

reduced condition of the last molar. 

The anterior lobe of the first cheek tooth is 

distinctly notched by an anterior ~edian reentrant angle, as is usual in Peromyscus, whereas in the living species of Eligmodontia this 

lobe is usually evenly convex in front. The 

fossil species from Arizona, however, is readily 

distinguished from Peromyscus by the characters which ally it to Eligmodontia, namely, 

by the form and position of the masseteric 

ridge, which extends forward to the extrem.e 

anterior border of the cheek-tooth series; by 

the form and situation of the capsular process 

for the reception of the base of the incisor, 

which is placed high upon the ascending ramus 

and is marked by a decided sulcus between it 

and the coronoid; and by the form of the last 

cheek tooth, which in species of Eligmodontia 

is more reduced than in Peromyscus. 

Onychomys pedroensis Gidley, n. sp. 

Plate XXXV, figure 1. 

Type.-Portion of a left lower jaw carrying 

the first and last cheek teeth (catalog No. 

10506, U.S. Nat. Mus,). 

Paratypes.-Other lower jaw portions (catalog Nos. 10507, 1Q508, U.S. Nat. Mus.). 

Locality.-All from Curtis ·locality. 

Description.-Length of · the cheek teeth 

4.5 millimeters; size somewhat larger than 

0. leu. ruidosae, which it so~ewhat more 

nearly resembles than any other living species. 

It further differs from that species in its relatively greater depth of jaw, the greater degree 

to which the masseteric ridge is carried forward, and the somewhat less reduced condition of the last cheek tooth. 

Onychomys bensoni Gidley, n. sp. 

Plate XXXV, figure 3. 

Type.-Portion- of a right lower jaw containing complete dentition (catalog No. 10509, 

U., S. Nat. Mus.). 

Locality.-Benson locality. 

Description.-Length of cheek-tooth series 

3.9 millimeters; about the size of 0. torridus 

but with less reduced last molar, as in the 

larger sp~cies 0. leu. ruidosae. The hinder lol;>e 

91048°-23-9 

of the last molar is less reduced even than in 

the last-mentioned species. 0. bensoni differs 

from all the living species of the genus in 

having more widely open valleys and less conspicuous lophs in the mola_r teeth; a more 

depressed heel on the last lower molar, which 

is distinctly lower than the anterior or triconid 

portion; and apparently a · relatively larger 

and higher coronoid process. 

Sigmodc;m curtisi Gidley, n. sp. 

Plate XXXV, figure 2. 

Type.-The greater parts of both lower jaws 

carrying complete dentition (catalog No. 10510, 

U.S. Nat. Mus.). 

Paratype.-Portion of a . right lower jaw 

.with cheek teeth (catalog No. 10511, U. S. 

Nat. Mus.). 

Locality.-Both from Curtis locality. 

Description.-Length of cheek-tooth series 

7 ~illimeters; about th'e size of S. hispidus 

arizonae, which it 1Seems to . r-esemble more 

nearly, but it differs from that as well as the 

other living specieg in the more open valleys of 

the reentrant angles, the . more compressed 

lophs, the less hypsodont condition of the 

cheek teeth, the relatively deeper posterior 

inner reentrant valley of p4 and m1, and especially the form and proportions of the cusps of 

the last lower molar, which is relatively larger, 

with the hinder · cusp relatively broader and 

fuller than in the living species. A feature 

that is characteristic of this and the species 

described below· and is not observed in any of 

the living species is noted in the last molar, in 

which the great extension and flattening of 

the inner or lingual wall .of the posterior lobe 

forms a sharp right angle -rith the posterior . 

wall of the reentrant angle on that side. 

I take pleasure in naming this species for 

Mr. Milton Curtis, in recognition of his efficient 

assistance in the field. 

Sigmodon minor Gidley, n. sp. 

Plate XXXV, figures 4, 5. 

Type.-Portion of a left lower jaw carrying 

the complete dentition (catalog No. 10512, 

U. S. Nat. Mus.). 

Paratype.-Portion of a left maxillary carry- . 

ing the anterior two cheek teeth (catalog No. 

10513, .U. S. Nat. Mus.). 

Locality.-Curtis locality. Five other lower-

·jaw portions, most of them with complete 
126 SHOR.TER CONTRJBUTIONS '1"0 GENERAL GEOLOGY, 1922. 

dentition (catalog Nos. 10514 to 10518), are 

also referable to this species. 

Description.-Length of cheek-tooth series 

4.7 millimeters; smaller than S. medius and 

decidedly smaller than any of the living 

species examined. This species is distinguished from the living forms by the same 

characters observed in S. medius, except that 

the external reentrant valleys of the upper 

molars (as shown by specimen No. 10513) are 

of the normal modern type. S. minor differs 

from S. medius only in its smaller size, having 

a relatively ' narrower anterior lower cheek 

tooth, in which the anterior lobe is relatively 

smaller, with the adjacent reentrant valleys 

nearly equal in length. The reentrant valleys 

of the upper cheek teeth are oblique to the 

same degree and of about the same proportionate depth, but the molar crowns of both 

the upper and lower series are less hypsodont. 

Sigmodon medius Gidley, n. sp. 

Plate XXXV, figures 6, 7. 

Type.-Portion of a right lq.wer jaw containing the complete dentition and an associated fragment of a right maxillary carrying 

the anterior two cheek teeth, possibly of the 

same individual (catalog No. 10519, U. S. 

Nat. Mus.). 

Paratypes.-Four other lower-jaw portions 

(catalog Nos. 10520 to 10523, U.S. Nat. Mus.). 

Locality.-All from the Benson locality. 

Description.-Length of cheek-tooth series 5.5 

millimeters; somewhat smaller than the living 

species S. sanctae martae, with which it seems 

to compare more nearly than with other living 

forms. Its resemblances are noted in the form 

of the anterior lobe of the first cheek tooth, in 

which the anterior internal reentrant valley 

. considerably exceeds the opposing outer one in 

length; in the decided angulation of the posterior portion of the inner wall of the last molar; 

and in the relatively heavy symphysis and 

considerable depth of jaw. It differs from 

this and other living species in having the 

cheek-tooth crowns slightly less . hypsodont, , 

the reentrant valleys more open, and the lophs 

correspondingly narrower, while there is present 

in t4e last molar a small but distinct reentrant 

notch on its inner side opposite the posterior 

reentrant valley. 

The two upper ·cheek teeth show the same 

character of the more open valleys observed in 

the lower cheek · teeth. Another difference 

noted is the form of the external reentrant 

valleys of these teeth, which clearly distinguishes them from the corresponding teeth of 

living species. The external reentrant valleys, 

instead of being straight, open directly outward, while their inner portions bend backward, 

forming a decided angle in their posterior 

enamel walls. In the living species these valleys run obliquely forward and outward in a 

nearly straight or but slightly curved line. 

Two other lower jaws in the collection (Nos. 

10521 and 10522) differ slightly in minor characters from the type but are here referred to 

this species. These differences, which consist 

wholly in a somewhat smaller size and a less 

proportionate depth of jaw, correspond to 

differences observed between males an females 

of the living species. S. sanctae martae. I 

therefore assume that the type specimen and 

specimen No. 10520, which agrees with it in 

every particular, represent males, while the 

smaller jaws just mentioned represent females 

of the species. 

Neotoma fossilis Gidley, n. sp. 

. Plate XXXV, figures 8-10. 

Type.-Portion of a right maxillary carrying 

the anterior cheek tooth and the alveoli for 

middle cheek tooth (catalog No. 10524, U. S. 

Nat. Mus.). 

Paratypes.-Portion of a left lower jaw carrying the incisor and alveoli for the cheek teeth, 

and two right lower cheek teeth (catalog Nos. 

10525 and 10526, U. S. Nat. Mus.). 

Locality.-Benson locality. 

Description.~Length of anterior cheek tooth 

3.2 millimeters; width 2.2 m,illimeters; about 

the size of N. intermedia gilva. The following 

characters distinguished this from all living 

species: First upper cheek tooth relatively 

short and wide; no indication of an· anterior 

internal reentrant valley; posterior internal 

reentrant valley nearly as long as the the external one; posterior notch of anterior palatial 

opening opposite the anterior: root of the first 

cheek tooth. · 

The two lower teeth referred to this species 

also show distinctive characters. The anterior one (p4) is entirely devoid of the anterior 

reentrant valley so prominent in such a form as 

N. cinera, and both these teeth are like the· 

corresponding ones of this species in h~ ving the 
FOSSIL VERTEBRATES OF THE SAN PEDRO VALLEY, ARIZONA. 127 

posterior external reentrant valleys pitted in a 

way to form a nearly circular enamellJke in 

well-worn teeth. These lower teeth differ from 

those of all living species in having_ the main 

cross lophs directed somewhat obliquely inward and backward instead of squarely across 

the long axis of the tooth. I 

The lower-jaw specimen shows nothing peculiar except that the capsular bulb at the base of 

the incisor is somewhat less prominent than is 

usual in the living species. 

N eo fiber sp. 

Plate XXXV, figure 14. 

A nearly complete cheek tooth, apparently 

the left upper middle one; from the Curtis 

locality (catalog No. 10527, U. S. Nat. Mus.), 

seems to represent the genus Neofiber. It is 

slightly smaller than the corresponding tooth of 

Neofiber alleni, with which I compared it, but 

has all its characteristics. Except the slight 

variation in size, they differ only in that the 

base of the fossil tooth is closed by the formation of rootlets, whereas th~ specimens of the 

living species examined seemed to indicate 

g~owth from a persistent pulp. However, this 

difference may be, in part, at least, an age 

character, as in the closely related genus Ondatra, in which both conditions are found on 

examm1ng a number of· specimens of various 

ages. 

Order LAGOMORPHA. 

Four species of Lagomorpha are represented 

in the collection, three from th~ Benson locality 

and one from the Curtis locality. They seem 

not to be referable to any living species, but the 

material representing them is too fragmentary 

to warrant any attempt at diagnostic descriptions. 

Species No. 1. 

Plate XXXV, figure 15. 

Represented ·by a portion of a left lower jaw 

carrying p4, m11 m2 (broken), and the alveoli 

for the other two cheek teeth and the incisor; 

from the Benson locality (catalog No. 10530, 

. U. S. Nat. Mus.). This specimen represents a 

species about the -size of Lepus campestris, or 

slightly smaller, and it agrees with that species 

r~ther closely both in jaw and tooth characters. 

Species No. 2. 

Plate XXXV, figure 11. 

Represented by two upper incisors (broken), 

a first lower cheek 'tooth of the left side, and a 

median lower cheek tooth of the left side, from 

the Benson locality (catalog No. 10529, U. S. 

Nat. Mus.). 

These teeth represent a sm.all species about 

the size of Sylvilagus aud. arizonae or Brachylagus idahoensis. However, ·there are some 

peculiarities in one or another of all these teeth 

that make uncertain their definite reference to 

either of these living genera. The incisors are· 

of a type to fit in with either genus, although 

there is not quite the difference in relative size 

·of the two lobes formed by the anterior longitudinal groove. In the molar tooth the posterior 

lobe is about intermediate in relative size bebetween that of S. aud. arizonae and B. idahoensis, and both lobes are somewhat less laterally 

expanded and less sharply angulate than in 

either of these species. The anterior lower c4eek 

tooth, which is of the right side, is peculiar and 

differs from that of any living species that has 

come under my observation. It is of the same 

general form as that of S. aud. arizonae but is 

proportionately a little wider, being nearly as 

wide as long, and is void of any reentrant angles 

except the normal two outer ones. Moreover, 

the posterior one of these extends but little 

more than halfway across the tooth. In aU 

living forms examined this reentrant either 

extends entirely across to the inner wall of the 

tooth or -meets an opposing reentrant from the 

inner side. 

Species No.3 • . 

Plate XXXV, figure 13. 

In the collection from the Curtis locality 

are a portion of a right lower jaw carrying the 

anterior two cheek teeth (catalog No. 10528, 

U.S.Nat.Mus.) and a lower right anterior tooth 

of a· second individual, which represent a species 

about the size of Lepus californicus erennicus, 

or somewhat smaller. The fossil- spedes 

seems to differ from the latter, however, in the 

proportions of all the tooth lobes which are 

somewhat narrower and in having the anterior 

lobe of the first cheek and tooth set farther inward, so that the reentrant valley faces decidedly 

forward and outward, instead of almost directly 

outward, as in the living species. 
128 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1922. 

Cf. Lepus sp. 

Plate XXXV, :figure 12. 

A fourth species of Lagomorpha (catalog 

No. 10535, U. S. Nat. Mus.1 is represented in 

the material from the Benson locality by the 

two incisors of the right side in a fragment of 

the premaxillary. It differs from the others 

in having an unusually high inner ridge on the 

large incisor. In fact, the tooth is remarkable 

in that the plane of its upper face is very oblique 

to the perpendicular plane of' the skull, as 

in Ochotona, but the plane of its lower surfaces 

is nearly at -right angles to the perpendicular 

median plane of the skull, as in the true rabbits, 

and its summit has the characteristic wear of a 

short anterior chisel point and posterior ledge 

or shelf observed in all species of rabbits but not 

found in· the Pica group. The longitudinal 

enamel groove is filled with cement, but this 

feature has not even a generic significance. 

As this form of incis~r is suggested in some 

degree in certain species of Lepus, as L. 

.siamensis, I regard the fossil specimen as belonging to that genus. 
. I 

PLATES XX~IV-XXXV. 

I 

I 

129 

I , 

I • 

I 
PLATE XXXIV. 

[All figures about twice natural size.] 

Page. 

FIGURE 1. Citellus cochisei Gidley, n. sp. Type. Upper cheek teeth of right side, Grown view. No. 10490, 

U. B. Nat·. Mus ........................................................ ·..................... 121 

2. Citellus cochisei Gidley, n. sp. Portion of left lower jaw, tooth-crown view; 2a, side view. No. 

10491, U.S. Nat. Mus....................................................................... 121 

3. Citellus bensoni Gidley, n. sp. Type. Last left upper molar, crown view; 3a, 3b, right upper molar 

probably of same individual. No. 10531, U. S. Nat. Mus..................................... 122 

4. Citellus bensoni Gidley, n. sp. Lower cheek teeth in fragment of jaw of left side, crown view. No. 

10532, U. S. Nat. Mus...................................................................... 122 

5. Geomys parvidens Gidley, n. sp. Type. Anterior portion of skull, palate view; 5a, side view. 

No. 10492, U.S. Nat. Mus.................................................................. 122 

6. Geomys parvidens Gidley, n. sp. Portion of a right lower jaw, tooth-crown view; 6a, side view. No. 

10493, U.S. Nat. Mus...................................................................... 122 

7. Geomys minor Gidley, n. sp. Type. Portion of a right lower jaw, tooth-crown view; 7a, side view. 

No.10494, U.S. Nat. Mus ................. ~---············································· 123 

8. Geomys minor Gidley, n. sp. Upper incisor of left side, front view. No. 10534, U. S. Nat. Mus... 123 

9. Cratogeomys bensoni Gidley, n. sp. Type. Portion of a left lower jaw, tooth-crown view; 9a, side 

view. No. 10495, U. S. Nat. Mus ... . ·................ ~........ ............................. 123 

10. Cratogeomys bensoni Gidley, n. sp. Portion of a right lower jaw, tooth-crown view; lOa, side view. 

No. 10497, U.S. Nat. Mus................................................................. 123 

11. Cratogeomys bensoni Gidley, n. sp. Upper incisor of right side, front view. No. 10496, U. S. Nat. 

Mus ................................................. ,........ . ........................... 123 

12. Peromyscus brachygnathus Gidley, n. sp. Type. Portion of a right lower jaw, tooth-crown view; 

12a, side view. No. 10501, U. S. Nat. Mus ............ ~..................................... 124 

13. Peromyscus minimus Gidley, .n. sp. Type. Portion of a left lower jaw, tooth-crown view; 13a, 

side view. No. 10500, U.S. Nat. Mus ... :................................................... 124 

14. Peromyscus sp. Portion of a right lower jaw, side view. No. 10502, U.S. Nat. Mus ............. ·... 124 

15. Eligmodontia arizonae Gidley, n. sp. Type. Greate;r portion of a right lower jaw, crown view; 

15a, side view. No. 10503, U. S. Nat. Mus.................................................. 124 

16. Dipodomys minor Gidley, n. sp. Type. Greater portion of ~ right lower jaw, tooth-crown view; 

16a, side view. No. 10499, U.S. Nat. Mus ............................... ,.................. 123 

130 
U. B. GEOLOGICAL SURVEEY PROFESSIONAL PAPER 131 PLATE XXXIV 

3a 

2a • 3b 

4 

5 

7a 

9 

6a 7 

11 

9a 

10 

16 

12a 

lOa 

13 16a 

13a 14 

15a 15 

FOSSIL VERTEBRATES OF SAN PEDRO VALLEY, ARIZ. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 131 PLATE XXXV 

4 

1 

1a. Sa 4a 

2a 

7 

5 

6a 8a 

11a 

12 12a 

lOa 

13 13a 14 

14a 

l5a 

FOSSIL VERTEBRATES OF SAN PEDRO VALLEY, ARIZ. 
PLATE XXXV. 

[All figures about twice natural size.] 

Page. 

FIGURE 1. ' Onychomys pedroensis Gidley, n. sp. Type. Portion of a left lower jaw, tooth-crown view; la, side 

view. No.l0506, U.S. Nat. Mus............................................................ 125 · 

2. Sigmodon curtisi Gidley, n. sp. Type. Portion of a right lower jaw, tooth-crown view; 2a,, side 

view. No.10510, U.S. Nat. Mus ................................................... :........ 125 

3. Onychomys bensoni Gidley, n. sp. Type. Portion of a left lower jaw, tooth-crown view; 3a1 side 

view. No.10509, U.S. Nat. Mus............................................................ 125 

4. Sigmodon minor Gidley, n. sp. Type. Portion of a left lower jaw, tooth-crown view; 4a, side view. 

No.10512, U.S. Nat. Mus .......................... .'........................................ 125 

5. SigmoJon minor Gidley, n. sp. Two anterior cheek teeth in fragment of left maxillary, inner-side 

view. No. 10513, U.S. Nat. Mus............................................................. 125 

6. Sigmodon medius Gidley, n . sp. Type. Portion of a right lower jaw, tootl crown view; 6a, side 

view. No.l0519, U.S. Nat. Mus........................................ . .................... 126 

7. Sigmodon medius Gidley, n . sp. Anterior two upper cheek teeth of right si :~ e, in fragment of jaw, , 

crown view. No. 10519, U.S. Nat. Mus .. . ...................... : ............................ 126 

8. Neotomafossilis Gidley, n. sp. Portion of a left lower jaw viewed from above; 8a, side view. No. 

10525, U.S. Nat. Mus........................................................................ 126 

9. Neotomafossilis Gidley, n. sp. Type_. First upper cheek tooth of right side in fragment of maxillary, 

crown view. No. 10524, U. S. Nat. Mus .......................................... _ ... _....... 126 

10. Neotomafossilis Gidley, n. sp. Anterior two lower cheek teeth of right side, crown view; lOa, inner 

side view. No. 10526, U.S. Nat. Mus. : ..................... _ . ............................... · 126 

11. cf. Sylvilagus sp. Median incisors in fragment of premaxillary, palate view; lla, front view. No. 

10529, U.S. Nat. Mus ......... "················-·-········································--- -127 

12. Lepus sp. Two upper incisors of right side in fragment of premaxillary, palate view; 12a, front view. 

No. 10535, U.S. Nat. Mus.................................................................. 128 

13. Lepus sp. cf. L. californiC'lts. Anterior two cheek teeth of right side in fragment of lower jaw, crown 

view; 13a, outer side view. No. 10528, U. S. Nat. Mus_ ........... , ...................... _..... 127 

14. Neofiber sp. Portion of a left upper molar, oblique crown view; 14a, outer side view. No. 10527, 

U S. Nat. Mus ___ ._ ..... _ ... __ . _____ . _. _ ... _. _. _ ... _. _. _ .......... _ ...... __ .. ___ .......... _ 127 

15. Lepus sp. Portion of left lower jaw, tooth-crown view; 15a; side view. No. 10530, U.S. Nat. Mus._ 127 

131 

\