Chapter II: Part 2

The shape and dimensions of the incisive foramen long have been recognized as providing specific characters. Large size of the foramen is probably correlated with the requirement for a large amount of moisture reaching Jacobson's organ in the nasopalatine space; the moistening of the sensory epithelium is certainly involved. There seems to be a certain correlation between small size of the incisive foramen and high degree of humidity in the environment. Shapes and dimensions of the foramen appear as simple or multiple biotypes and provide characters which can be employed to differentiate subspecies, species and even subgenera. Usually a character, say a general shape, occurs in nearly all populations of a given subspecies but the particular shape seems to be more closely correlated with ecological conditions, especially humidity. Animals which live far away from large rivers usually have larger foramina than animals which live close to rivers.

Both the premaxilla and the maxilla develop processes which form a sheath for the vomer. This vomerine sheath forms a bridge which longitudinally crosses the incisive foramen; the structure of this bridge varies widely. Sometimes the maxillary part is not developed and the sheath is incomplete posteriorly; sometimes this maxillary part is very slender and merely touches the premaxillary part. The premaxillary part, however, is always well developed.

Teeth

Considered by itself the variation in the tooth pattern can lead to erroneous conclusions as to differentiation of species, because the number of folds on the occlusal face of a tooth and the depth of certain folds may be subject to great individual variation as shown by examination of more than one large series of specimens of the same kind, age and sex from a single locality. Also there are geographic gradients or clines, in number of folds. Nevertheless the variation in number of folds, when measured at sufficient intervals along a cline, may provide quantitative characters useful in differentiating subspecies.

FIGS. 2-9. _Proechimys_ (_Proechimys_) _semispinosus liminalis_,
female, MN no. 6243, Rio Quichito. Fig. 2, unworn crown. Figs. 3-8,
cross sections at 0.5 mm. intervals, showing changes in the main fold
and counterfolds at increasing depths as the tooth was ground down.
Fig. 8 is 3 mm. below surface shown in fig. 2. Fig. 9, posterior view
with proximal end of the tooth open showing basal ends of folds.
Later in life the proximal end closes and three roots are formed.

FIGS. 10-17. _Proechimys_ (_Trinomys_) _iheringi denigratus_, female,
SEPFA no. 17060, Mata do Ribeirão da Fortuna. Figs. 10-16
corresponding to figs. 2-8. Fig. 17, posterioventral view with
proximal end of the tooth open and part of walls cut away, showing
basal ends of folds. Later in life, as in _Proechimys_, the proximal
end closes and three roots are formed. ]

The main fold involves both the occlusal face of the tooth and the side wall. The counterfolds, which are smaller counterparts of the main fold, in most instances also implicate the wall of the tooth opposite to that marked by the main fold, but are to be seen mostly on only the occlusal face of the tooth. Unerupted teeth with the crowns unworn and other teeth which had barely broken through the gums were ground down to permit the making of drawings of the surfaces at different levels. This study revealed that the main fold is deepest in the wall of the tooth. The development of the main fold varies in two different ways: in all samples from southeastern and eastern Brazil it is strongly developed, deeply grooves the tooth through its crown and, in younger individuals, completely divides the occlusal surface of the tooth. As use wears down the crown, the main fold soon becomes separated from the opposite wall and then gradually shortens toward its basal portion. In the other type, common to animals of all the remaining part of the range of the genus, the main fold is rather short, never reaching the opposite wall. In this case, however, one of the counterfolds usually appears almost opposite the main fold in such a way that in non-erupted or just-erupted teeth the main fold and one counterfold may be connected by a shallow groove that may give the impression of extension of the main fold and, therefore, lead to false interpretations. Closer examination shows that the counterfold which apparently meets the main fold is really situated anteriorly or posteriorly to it, in upper or lower teeth respectively. One subspecies in the subgenus _Trinomys_ differs from the general characteristics of the subgenus in sometimes showing a small main fold in P4 whereas it is large in all other cheekteeth. The structural differences here mentioned in the main fold were never before recognized. Therefore, the meaning of "quadrilaminate" pattern, "three outer folds" or "three inner folds" (of authors) is not consistent insofar as the two groups are concerned.

Writers have more or less tacitly admitted three as the usual number of counterfolds present in the upper molariform teeth. Ellerman, for example (1940:117), states: "Upper cheekteeth normally with three outer and one inner folds each, these soon becoming isolated as islands. A few species, which will be discussed below, vary slightly in pattern." Thomas (1921:140) erected the subgenus _Trinomys_ on the basis of the upper molariform teeth having only three laminae. Actually a meticulous study of widely varying samples shows that the number of counterfolds may vary from _one_ to _five_, the usual number being three or four. One of the most important facts to record on this subject is that young specimens with slightly worn molariform teeth are more apt than either adult or younger specimens to show the maximum number of counterfolds. Usually nonworn teeth show rounded crests and valleys of different depth. For example, it is common to see one continuous groove giving the impression of a main fold crossing the occlusal surface transversely. The slightest wear of the occlusal surface, however, shows that really there are two valleys instead of one. The two are the main fold and one counterfold. In this case, it would be easy to confuse the two types of teeth, one with the main fold short and the other with the main fold extending almost all the way across the occlusal surface.

Some of the counterfolds are especially shallow and tend to disappear in an early stage of wear, and adult individuals may have these folds completely worn away. Advanced wear usually develops a cuplike occlusal surface with only the remains of the main fold and also remains of one or more counterfolds represented by small enamel islands (Figs. 2 to 17). In the form _Proechimys iheringi iheringi_, for example, every tooth shows three counterfolds in the upper molariform teeth of individuals in which the wear is not advanced. This number, however, is less in all or part of the molariform teeth of older individuals.

Adjacent counterfolds may appear to be coalesced in many instances. Coalescence is more likely to be seen in species where a wider variation in the number of the counterfolds is involved and it appears as a gradient in the reduction of the number of counterfolds.

Of great importance, as a general feature of molariform teeth, is the relative size as related to the geographical distribution, showing, again, a natural division in the genus. In all forms of southeastern Brazil the premolars are larger than the first molars, the first molars are larger than the second molars, and the second molars are larger than the third molars. The forms from central and northern Bahia, Brazil, have the molariform teeth more or less the same size. The forms from the remaining part of the area occupied by the genus have premolars smaller than the first molars, the first molars smaller than the second molars, but the second molars larger than third ones.

HABITS

_P. dimidiatus_ was studied in the field and laboratory. _P. dimidiatus_ in captivity showed regular diurnal activity, coming out of the nest for food at intervals. Individuals were fed a cereal mixture and nuts of small size. The animals usually buried the nuts in the sand of the outer cage. While holding the nut with the mouth and front feet, the animal patted the sand rapidly, thus burying the nut, and it then pushed more sand over the place with the front feet.

Sometimes the emergence from the nest is followed by a long yawning and stretching ceremony. The animal spreads the fore and hind legs widely apart, while the back is curved down and the head and tail turn upward. Then one of the hind legs is stretched backward and, at the same time, the mouth is opened widely and the tail is moved in an undulatory fashion. The operation may be repeated using the other legs, or not.

_P. dimidiatus_ was regularly found in climax forest. The best shelter and nesting ground was usually under boulders, commonly not farther than 10 meters from water. The entrance to the nest was kept clean. No more than two adult animals (male and female) were captured in the same shelter, and only a few times were young captured in the same place with adults. Nesting places were located also at the bases of trees and near fallen logs where litter accumulates.

Records of animals kept in captivity show that the species _dimidiatus_ survives more than two years. Specimen MN no. 5448 [M] was adult when captured by the Serviços de Estudos e Pesquisas sobre a Febre Amarela on December 5, 1938, and died on January 17, 1942. Therefore, it lived for more than 1,139 days.

_Proechimys dimidiatus_, in Rio de Janeiro, as well as _P. i. bonafidei_ and _P. i. iheringi_ which live in the same region, were found breeding from September to November and from March to May. _Proechimys longicaudatus roberti_, in Anapolis, Goiaz, was found breeding from July to November and from January to March. _P. g. hyleae_ and _P. g. leioprimna_ in the lower Tapajoz and lower Tocantins rivers, Pará, were found breeding in January.

It seems that in the Central Plateau and southeastern Brazil, _Proechimys_ has two litters per year, one in the early spring and a second in the late summer. The number of young per litter varies from 1 to 5, although 2 is the usual number.

CHANGES WITH AGE

_Juveniles._--The animals are born with a thick pelage of thin aristiforms and thin setiforms. The color is uniformly blackish brown. The nose, hands, feet, ears and tail are pinkish; P4 and M1 are already erupted and the second molars are included in the bony alveoli. The incisors are orthodont; the rostrum is short and the braincase is wide. The posterior part of the skull is greatly curved dorsally. No change is noticed in the pelage before the second molars erupt and become functional.

_Adolescents._--As soon as the second molars become functional, the pelage starts molting on the back. The thin aristiforms are still in place but the aristiforms of the adult pelage may be noticed growing under them in an oval patch which extends from behind the shoulders caudad to the hips. At that age the first, agouti-colored aristiforms appear on the mystacial region, immediately behind the vibrissiforms. The rostrum gradually lengthens and the braincase appears to become less inflated.

By the time the third molars erupt, the aristiforms start showing among the setiforms which are now changing to agouti color in the same area on the back, while the thin aristiforms of the juvenal stage disappear. The agouti setiforms are appearing also posteriorly from the mystacial region to the sides of the head and neck and, at the same time, on the frontal region. The patch of glossy aristiforms and setiforms on the back is sharply differentiated from the dull juvenal pelage of the sides and rump. In a later stage the area of agouti setiforms on the sides of the neck extends to the outer sides of the arms and finally reaches the area on the back where the agouti setiforms were already developed.

_Adults._--When the third molars become functional, the agouti setiforms are in place except for those on the upper sides of the neck. The aristiforms have now extended over their normal area of distribution. As soon as the third molars show wear, the premolars and first molars have the counterfolds isolated in the occlusal surfaces as enamel islands. Wearing gradually isolates all counterfolds.

_Senile_ individuals.--Progression of wear soon eliminates the signs of the shallowest counterfolds from the occlusal surface and finally the tooth is reduced to a short crown with a cuplike occlusal surface completely filled with dentine. Only the main fold usually remains; it is more or less reduced in size.

From the records of the Serviços de Estudos e Pesquisas sobre a Febre Amarela, the following data for males of _Proechimys longicaudatus roberti_ were obtained:

======================+=========+==========+========+=========+=======
| Number | | Length | | Length
AGE | of | Weight | of head| Length | of
| cheek- | in grams | and | of tail | hind
| teeth | | body | | foot
----------------------+---------+----------+--------+---------+-------
One day old | 2 | 20.5 | 70 | 53 | 24
17 days old | 2 | 26.0 | 110 | 60 | 28
Juvenile | 2 | 85.0 | 150 | 105 | 39
Adolescent | 3 | 115.0 | 175 | 120 | 45
Adolescent (older) | 3 | 180.0 | 195 | 135 | 45
Adult | 4 | 200.0 | 223 | 158 | 48
Senile individual | 4 | 360.0 | 230 | 170 | 48
----------------------+---------+----------+--------+---------+-------

The weights and measurements (except for one- and 17-day-old animals) represent averages of specimens of the different ages.

Genus =Proechimys= J. A. Allen

_Genotype._--_Echimys trinitatis_ Allen and Chapman, by original designation.

_Proechimys_ Allen and Chapman, 26 December 1899, Bull. Amer. Mus.
Nat. Hist., 12(20):264, orig. description; Tate, 1935, Bull. Amer.
Mus. Nat. Hist., 68(5):398; Ellerman, 1940, The families and genera
of living rodents, Brit. Mus. (Nat. Hist.), 1:115.

_General characters._--Muriform echimyids of medium size; pelage
with flattened and lanceolate and sometimes clavate aristiforms,
varying greatly in width and distributed over most of the dorsal
surface from shoulders to hips or base of tail; setiforms also
flattened, evenly distributed throughout; entire ventral surface
and inner sides of legs white or, rarely, invaded by some buffy
color; tail shorter than, equal to, or slightly longer than, head
and body, bicolored and with a few bristles between scales,
sometimes heavily penicillated; feet long and narrow; pollex
rudimentary; hallux shorter than fifth toe; ears wide and long;
mammae 2-1=6.

_Skull._--Generally elongate and strongly built, with supraorbital
ridges well developed, frequently extending across parietals
toward occipital region; zygomatic arches variable in depth,
always with postorbital process; infraorbital foramen with or
without lower groove for transmission of nerve; incisive foramen
usually large; vomerine sheath complete or incomplete;
mesopterygoid fossa extending forward at least to plane of third
molars; bullae large; angular process of mandible turned upward.

FIGS. 18-19. _Proechimys_ (_Proechimys_) _goeldii steerei_, sex ?,
USNM no. 105537, "Hyutanaham." Upper teeth at left (fig. 18).

FIGS. 20-21. _Proechimys_ (_Trinomys_) _dimidiatus_, male, MN no.
6256, Pedra Branca. ]

_Teeth._--Incisors opisthodont, orthodont or proodont, not grooved;
upper molariform teeth with a main internal fold and one to five
external counterfolds which usually appear as enamel islands in
worn teeth, these counterfolds barely implicating the lateral wall;
lower molariform teeth with folds as in the upper molariform teeth
except that they are reversed and the number of internal
counterfolds is usually fewer in the molars.

ARTIFICIAL KEY TO THE SUBGENERA AND SPECIES

1. (_a_) Tail less than 90 per cent of head and body; aristiforms
not evident on outer thighs and rump; skull
with ridges across parietals; size of upper cheekteeth
increasing from P4 to M2; main fold small.
subgenus PROECHIMYS, 2

(_b_) Tail 90 per cent or more of head and body; aristiforms
evident on outer thighs and rump; skull with
no ridges across parietals; size of upper cheekteeth
decreasing from P4 to M3; main fold large.
subgenus TRINOMYS, 5

2. (_a_) One or more upper molars with four counterfolds 3
(_b_) Upper molars with no more than three counterfolds, 4

3. (_a_) Aristiforms wide (more than 0.7 mm). _P. semispinosus_, p. 342
(_b_) Aristiforms narrow (less than 0.7 mm) _P. goeldii_, p. 338

4. (_a_) Aristiforms wide (0.9 mm or more), or narrow (0.6
to 0.7 mm) but then with only two counterfolds in
each lower molar _P. guyannensis_, p. 355
(_b_) Aristiforms narrow (0.5 to 0.65 mm) but with one or
more lower molars having three counterfolds.
_P. longicaudatus_, p. 346

5. (_a_) Aristiforms narrow (0.5 mm) and limber; no differentiated
light-colored aristiforms on outer thighs and
rump; incisive foramen short and widest posteriorly
_P. dimidiatus_, p. 371
(_b_) Aristiforms 0.6 mm or more and stiff; differentiated
light-colored aristiforms on outer thighs and rump;
incisive foramen elongated and constricted posteriorly 6

6. (_a_) Skull large, more than 50 mm in total length, incisors
opisthodont _P. iheringi_, p. 373
(_b_) Skull small, less than 49 mm in total length, incisors
orthodont or proodont 7

7. (_a_) No clavate aristiforms, tail with white tip,
_P. setosus_, p. 384
(_b_) Clavate aristiforms among the ordinary ones, tail
without white tip _P. albispinus_, p. 388

Subgenus =Proechimys= J. A. Allen

_General characters._--Pelage with lanceolate aristiforms limited
to an area on the dorsal surface between the shoulders and the
hips; length of tail less than 90 per cent of length of head and
body; skull with conspicuous ridges; extension of supraorbital
ridges always evident on parietals; infraorbital foramen usually
with separate groove for transmission of nerve; palate usually
extended posteriorly as far as third molars; incisors opisthodont;
molariform teeth with a small main fold, never extended
transversely to opposite wall in occlusal surface of tooth; usually
one counterfold anterior to main fold in upper molariform teeth and
posterior to main fold in lower molariform teeth; premolars usually
smaller than first molars, first molars smaller than second molars
but second molars larger than third molars.

=Proechimys goeldii= Thomas

_General characters._--Size large; tail short; aristiforms narrow
and soft, usually concealed in pelage by setiforms; general color
of upper parts some tint of orange, gradually becoming lighter on
sides with no conspicuous, dark longitudinal band on back; feet
dark; ventral surface of body and inner side of legs white but
sometimes with some buff locally; skull broad and strongly built
but not conspicuously ridged; zygomatic expanse great and rostrum
not elongate; incisive foramen narrow; bullae large and inflated;
upper molariform teeth with three to four counterfolds, M3
ordinarily with four; lower premolars with four, and molars with
three, counterfolds.

=Proechimys goeldii steerei= Goldman

_Proechimys steerei_ Goldman, Proc. Biol. Soc. Washington, 24:238,
28 November 1911 (original description); Goldman, 1912, Proc. Biol.
Soc. Washington, 25:186; Tate, 1935, Bull. Amer. Mus. Nat. Hist.,
68(5):400; Ellerman, 1940, The families and genera of living
rodents, Brit. Mus. (Nat. Hist.), 1:119; Osgood, 1944, Zool. Ser.
Field Mus. Nat. Hist., 29(13):204.

_Type locality._--Hyutanaham, Upper Purus, _Lábrea_, Amazonas,
Brazil. _Type:_ United States National Museum, no. 105535, adult
male; collected in 1901 by Prof. J. B. Steere.

_Range._--Known only from the type locality and Porto Velho.

_Diagnosis._--Upper parts Mars Orange on back, grading to
Ochraceous-Tawny on sides; zygomatic breadth narrow; nasals short;
incisive foramen narrow and short; vomerine sheath complete and
thick; upper molars usually with four counterfolds.

_Pelage._--_Aristiforms on middorsal region_: Grayish basally,
gradually blackening toward tip; total length, 16 to 19 mm;
maximum width, 0.5 mm. _Setiforms on middorsal region_: Grayish on
basal third, gradually blackening toward tip but interrupted by a
Mars Orange, subapical zone 1.5 mm long; total length, 16 to 19
mm; maximum width, 0.06 mm. _Setiforms on outer thighs_: Whitish
basally, gradually blackening toward tip but interrupted by Orange
Rufous or Ochraceous-Tawny, subapical zone; total length, 14 to 16
mm; maximum width, 0.05 mm.

_Skull._--Large and strong; rostrum rather pointed posteriorly;
supraorbital ridges not much expanded and extending across
anterior half of parietals; infraorbital foramen without groove
for transmission of nerve, or groove obsolete; zygomatic arches
slender; postorbital process of zygoma involving mostly squamosal;
incisive foramen short and narrow (4.5 × 2.5 mm) with margins
almost parallel or tapering gradually caudad and extending toward
palate as ridges; posterior margin of incisive foramen
approximately 2.5 mm anterior to premolars; vomerine sheath
complete, with both elements well-developed; mesopterygoid fossa
never extending anterior to middle of M3; bullae large, well
inflated and with shallow grooves.

_Teeth._--Upper molariform teeth: P4 with three counterfolds;
upper molars with four counterfolds each or, less commonly, three.
Lower premolars with four counterfolds; lower molars with three
each.

_Comparisons._--From _P. g. goeldii_, _steerei_ differs in: Back
and sides with more reddish; narrower interorbitally and across
zygomata; palatilar length less and nasals shorter; maxillary part
of vomerine sheath thicker; usually four instead of three
counterfolds in M3.

_Remarks._--This subspecies is clearly related to _P. goeldii_. One skull from Porto Velho, Rio Madeira, _Guaporé_, Brazil (CNHM no. 21558) may belong to an unnamed subspecies but is provisionally included here.

In the field notes of Professor Joseph Beal Steere, an entry for no. 72 reads: "Big white bellied wood rats x two young found in nest of grass on the ground with the two young--_much darker_ young female." No. 77 in his field notes corresponds to the type specimen.

_Specimens examined._--Total number, 4, from Brazil, as follows:
Amazonas. _Lábrea_, Hyutanaham, 3 (USNM); Territ. Guaporé, Porto
Velho, 1 (CNHM).

=Proechimys goeldii goeldii= Thomas

_Proechimys goeldii_ Thomas, June 1905, Ann. Mag. Nat. Hist., 15
(ser. 7):587, (orig. descr.); Thomas, 1912, Ann. Mag. Nat. Hist., 9
(ser. 8):89; Thomas, 1920, Ann. Mag. Nat. Hist., 6 (ser. 9):277,
Tate, 1935, Bull. Amer. Mus. Nat. Hist., 68(5):400; Osgood, 1944,
Zool. Ser. Field Mus. Nat. Hist., 29(13):199.

_Proechimys cayennensis goeldii_, Ellerman, 1940, The families and
genera of living rodents, Brit. Mus. (Nat. Hist.), 1:121.

_Type locality._--Santarem, _Santarem_, Pará, Brazil. Type: British
Museum (Nat. Hist.), no. 5.1.25.6, adult female; presented by Dr.
E. A. Goeldi.

_Range._--Margins of the Amazon, between Jamundá and Tapajoz
rivers.

_Diagnosis._--Upper parts Ochraceous-Tawny; wide across zygomata;
nasals of moderate length; incisive foramen long and narrow;
vomerine sheath complete but maxillary part slender; first and
second upper molars with four counterfolds.

_Pelage._--_Aristiforms on middorsal region_: Whitish basally and
gradually blackening toward tip which is extended as long, thin
filament; total length, 22 to 24 mm; maximum width, 0.5 mm.
_Setiforms on middorsal region_: Gray basally, gradually
blackening toward tip but interrupted by Ochraceous-Tawny,
subapical zone 3.3 mm long; total length, 19 to 21 mm; maximum
width, 0.06 mm. _Setiforms on outer thighs_: Whitish basally,
gradually blackening toward tip but interrupted by
Ochraceous-Tawny, subapical zone 3 mm long; total length 14 to 16
mm; maximum width, 0.04 mm.

_Skull._--Large and strong; nasals pointed posteriorly;
supraorbital ridges moderately developed and extended caudad
across anterior third of parietals; zygomatic arches strong;
postorbital process of zygoma involving mostly squamosal; incisive
foramen elongate and narrow (5 to 6.5 x 2.3 mm) with margins more
or less parallel and raised to form ridges which extend posteriorly
to within 3 mm of plane of premolars; vomerine sheath complete,
with maxillary part thin and extended caudad as medial crest;
mesopterygoid fossa extending forward as far as posterior faces
of second molars or slightly short thereof; bullae large and
inflated.

_Teeth._--Molariform teeth large, P4-M3 averaging more than 9 mm
in length. Upper molariform teeth: P4 and M3 with three
counterfolds; M1 and M2 with four counterfolds each. In lower
teeth, p4 with four counterfolds and each molar with three
counterfolds.

_Comparisons._--Differences from _P. g. steerei_ are given in the
account of that subspecies.

_Remarks._--Specimens from the type locality were not available. Specimens from Fazenda Paraiso, Faro, were relied upon as representative of the subspecies. These agree with the type according to Thomas (1912:89). However, the skin of the type was changed in color by preservative (Thomas, 1905:587) and the best skin he saw was from Faro (1912:89).

Thomas (1920:277) applied the name _goeldii_ also to specimens from Manacaparú, a place a short distance above Manaus on the Solimões (Amazon) River and from Acajutuba, near Manaus, on the Negro River. In referring to these specimens (2 from Manacaparú and 2 from Acajutuba) Thomas (_loc. cit._) said "Five molar laminae are frequently, if not invariably, present among these specimens." He did not, however, mention whether or not the number of laminae was constant in both M2 and M3. One specimen from Acajutuba, in the collection of Museu Nacional (MN no. 1973 [M]), actually has five laminae in M3, but the specimens in the American Museum from Faro agree absolutely with Thomas' original description of _goeldii_.

Osgood (1944:199) doubted that _goeldii_ was a valid species. Evidence that Osgood's doubt was unjustified is furnished by the fact that Thomas (1912:89) pointed out that his specimen from Faro agrees with the type. Likewise, my two specimens from Faro agree with the type insofar as it has been described. Thomas (1912:89) mentioned two additional skulls from the type locality which, he stated, agree with the type which was received from the Museu Goeldi, Pará.

_Specimens examined._--Total number, 4, from Brazil as follows:
Pará, _Faro_, Faro, Fazenda Paraiso, 2 (AMNH); Amazonas, _Manaus_,
Manaus, 1 skull (AMNH); Amazonas, _Manaus_, Acajutuba, 1 (MN).

_Additional records._--Total number, 7 (British Museum), from
Brazil, as follows: Pará, _Santarem_, Santarem (Thomas, 1912:89;
1920:277), 3; Amazonas, _Manaus_, Acajutuba (Thomas, 1920:277), 2;
_Manacaparú_, Manacaparú (Thomas, 1920:277), 2.

=Proechimys semispinosus= (Tomes)

_General characters._--Size large; tail short and hairy;
aristiforms wide and stiff, especially well-developed on back;
general color on upper parts some shade of ochraceous, usually much
darker on back and forming a conspicuous dorsal band; feet dark;
ventral surfaces and inner sides of legs white; skull elongate and
strong with ridges well developed; incisive foramen long and
narrow; bullae large; usually four counterfolds in M3 and M2;
usually three but sometimes four counterfolds in M1 and even P4;
lower premolar with four and lower molars with three counterfolds.

=Proechimys semispinosus liminalis= subspecies nova

_Type locality._--Rio Quichito, affluent from the south of the
Javarí River, near _Benjamin Constant_, Benjamin Constant,
Amazonas, Brazil. _Type_: Museu Nacional, no. 6253, adult female,
collected in August, 1942, by E. Parko.

_Range._--Known only from the type locality.

_Diagnosis._--Color uniformly dark, setiforms marked with
Ochraceous-Tawny; skull wide across zygomata; nasals short;
prepalatilar part of skull long; incisive foramen long and narrow;
vomerine sheath incomplete or complete; M2 and M3 almost always
with four counterfolds; M1 more rarely with four counterfolds.

_Pelage._--_Aristiforms on middorsal region_: Gray basally,
gradually blackening toward tip which is generally extended as a
filament; total length, 21 to 23 mm; maximum width, 0.9 to 1 mm.
_Setiforms on middorsal region_: Gray basally, gradually
blackening toward tip but interrupted by Ochraceous-Tawny,
subapical zone 3 mm long; total length, 22 to 24 mm; maximum
width, 0.06 mm. _Setiforms on outer thighs_: Whitish basally,
gradually blackening toward tip but interrupted by Ochraceous-Buff,
subapical zone 2.5 mm long; total length, 13 to 15 mm; maximum
width, 0.08 mm; some with gray base, blackening gradually toward
tip, without any subapical zone; some with Light Ochraceous-Tawny,
subapical zone.

_Skull._--Large and strongly built throughout; supraorbital ridges
expanded and thick, extending, in old specimens, across parietals
to anterior angles of interparietals; interparietal ridges always
conspicuous; rostrum elongated; nasals blunt posteriorly;
zygomatic arches strong; infraorbital foramen with
weakly-developed groove for transmission of nerve; postorbital
process of zygoma involving mostly squamosal; incisive foramen
averaging 6 x 2.7 mm, widest in middle part and posteriorly
constricted, with raised margins which do not extend across
maxillae as ridges; posterior margin of incisive foramen
approximately 1.5 mm anterior to plane of premolars; vomerine
sheath incomplete or, sometimes, complete but always with
maxillary part slender; mesopterygoid fossa not extending forward
past centers of third molars; bullae moderately developed.

_Teeth._--Upper molariform teeth: P4 always with three
counterfolds; M1 with three counterfolds in 9 of 10 specimens and
four counterfolds in remainder; M2 with four counterfolds in 7
specimens, three counterfolds in remainder; M3 with four
counterfolds in 6 specimens, three counterfolds in remainder.
Lower premolar always with four, and molars with three,
counterfolds.

_Comparisons._--From _P. s. semispinosus_, _liminalis_ differs in:
darker color; wider aristiforms; greater percentage of upper
molars with four counterfolds. From _P. s. amphichoricus_,
_liminalis_ differs in: lighter upper parts of almost uniform
color instead of with conspicuous, blackish, middorsal,
longitudinal band; more strongly built skull; longer incisive
foramen; vomerine sheath usually incomplete instead of always
complete.

_Specimens examined._--Total number, 10 (MN) from the type
locality.

=Proechimys semispinosus amphichoricus= subspecies nova

_Type locality._--Mount Duida, Esmeralda, _Amazonas_, Venezuela;
altitude 325 m. _Type_: American Museum of Natural History, no.
77020, adult male; collected 16 October 1920 by Olalla Bros.

_Range._--Headwaters of Negro and Orinoco rivers, along boundary
of Brazil and Venezuela.

_Diagnosis._--Color dark, blackish on middorsal area; subapical
zone of setiforms on back Buckthorn Brown, but many with distal
parts black; skull broad across zygomata; nasals long;
prepalatilar area of skull long; incisive foramen long and narrow;
vomerine sheath complete; upper molars usually with four
counterfolds but P4 usually with only three.

_Pelage._--_Aristiforms on middorsal region_: Grayish basally,
gradually blackening toward tip; total length, 18 to 20 mm;
maximum width, 0.8 to 1.0 mm. _Setiforms on middorsal region_:
Gray basally, gradually blackening toward tip but interrupted by a
light (16 i), Buckthorn Brown, subapical zone 2 mm long; total
length, 18 to 22 mm; maximum width, 0.03 mm. Most of them,
however, whitish basally, gradually blackening toward tip without
any distinctively-colored, subapical zone; total length, 24 to 26
mm; maximum width, 0.5 mm. _Setiforms on outer thighs_: Whitish
basally, gradually blackening toward tip but interrupted by an
Ochraceous-Buff, subapical zone 3.5 mm long; black tip short; total
length, 17 to 19 mm; maximum width, 0.05 mm.

_Skull._--Large and slender; rostrum elongate; nasals bluntly pointed posteriorly; supraorbital ridges thick (but not expanded) and extending across parietals but almost obsolete in middle part of parietals; infraorbital foramen with weakly-developed groove for transmission of nerve; postorbital process of zygoma involving mostly squamosal; incisive foramen 5.5 x 2.8 mm wide in anterior third, with margins constricted posteriorly and extending as ridges approximately 2 mm beyond posterior margin of incisive foramen; posterior margin of incisive foramen approximately 2.5 mm anterior to premolars; vomerine sheath complete with maxillary part weak and premaxillary part extending posteriorly beyond middle of incisive foramen; mesopterygoid fossa extending forward as far as middle of M3; bullae well inflated and elongated.

_Teeth._--P4 with four counterfolds in one of five specimens and with three in remainder; M1 with four counterfolds in three of five specimens and with three in remainder; M2 with three counterfolds in one specimen and with four in all four remaining specimens; M3 always with four counterfolds. Lower premolars with four counterfolds and lower molars with only three.

_Comparisons._--The subspecies is easily distinguishable from _P. s. angularis_ by: larger number of black setiforms on back, forming an almost black longitudinal band; more elongate skull; larger and longer bulla; longer incisive foramen which is more constricted posteriorly.

_Specimens examined._--Total number, 6 (AMNH), as follows:
Venezuela, territ. _Amazonas_, Esmeralda, Mt. Duida, altitude 325
m., 4; Venezuela, territ. _Amazonas_, Rio Cassiquiare, Quemapuré,
1; Brazil, Amazonas, _São Gabriel_, Rio Uaupés or Caiari, Tatú, 1.

=Proechimys semispinosus kermiti= Allen

_Proechimys kermiti_ Allen, 30 December 1915, Bull. Amer. Mus. Nat.
Hist., 34(22):629 (orig. descr.); Allen, 1916, Bull. Amer. Mus.
Nat. Hist., 35(30):569; Tate, 1935, Bull. Amer. Mus. Nat. Hist.,
68(5):400; Ellerman, 1940, The families and genera of living
rodents, Brit. Mus. (Nat. Hist.), 1:119.

_Type locality._--Lower Rio Solimões (up the Solimões 50 to 60
miles on the north bank of the river), _Manacaparú_, Amazonas,
Brazil. _Type_: American Museum of Natural History, no. 37124,
adult female; collected 20 April, 1914, by Leo E. Miller (Roosevelt
Brazilian Expedition).

_Range._--Known only from type locality.

_Diagnosis._--Upper parts Tawny, with darker longitudinal band on
back, gradually becoming Ochraceous-Buff on sides; zygomata widely
spread; nasals long; incisive foramen long; vomerine sheath
incomplete; only M3 with four counterfolds.

_Pelage._--_Aristiforms on middorsal region_: Grayish basally,
gradually blackening toward tip; total length, 18 to 20 mm;
maximum width, 0.8 mm. _Setiforms on middorsal region_: Grayish
basally, gradually blackening toward tip but interrupted by Tawny,
subapical zone 2 mm long; total length, 18 to 20 mm; maximum
width, 0.06 mm; some blackened toward tip without subapical zone.
_Setiforms on outer thighs_: Whitish basally, gradually blackening
toward tip but interrupted by Ochraceous-Buff, subapical zone
2.5 mm long; total length, 18 to 20 mm; maximum width, 0.05 mm.

_Skull._--Large, elongate, and strongly built; rostrum not
conspicuously elongated; nasals bluntly pointed posteriorly;
supraorbital ridges wide and extending posteriorly across parietals
almost to level of interparietal; infraorbital foramen with
moderate development of groove for transmission of nerve; zygomatic
arches slender; postorbital process of zygoma involving mostly
squamosal; incisive foramen 6.5 mm long and 2.7 mm wide, wider in
anterior third and gradually constricted posteriorly, with margins
extended toward palate as ridges; vomerine sheath incomplete,
maxillary part threadlike; mesopterygoid fossa extending forward as
far as anterior third of m3; bullae large and well inflated.

_Teeth._--P4 with three counterfolds; M3 with four counterfolds;
M1 and M2 with three counterfolds. Lower premolars with four
counterfolds; lower molars with three counterfolds.

_Comparisons._--From _P. s. amphichoricus_, _kermiti_ differs in:
upper parts Tawny instead of Buckthorn Brown; incisive foramen
longer and wider; vomerine sheath incomplete; only M3 instead of
usually all molars, with four counterfolds. From _P. s.
liminalis_, _kermiti_ differs in: upper parts Tawny instead of
Ochraceous-Tawny; aristiforms narrower; M3 only, instead of
usually M2 and M3, with four counterfolds.

_Specimens examined._--Only the type.

=Proechimys longicaudatus= (Rengger)

_General characters._--Size medium to large; tail short;
aristiforms long and narrow; general color on upper parts
Ochraceous-Buff to Ochraceous-Orange, finely and uniformly lined
with blackish and not forming evident dark band on back; feet
dorsally white or gray; underparts of body and inner sides of legs
white; skull elongate and slender with moderate ridges; incisive
foramen of medium size; vomerine sheath complete or incomplete;
bullae large and elongate; upper molariform teeth with three
counterfolds; lower molariform teeth with three counterfolds but
commonly one or two molars have only two although premolar may have
four.

_Remarks._--The identity of "_Echimys longicaudatus_ Rengger" can be ascertained only after samples have been collected in the area indicated by Rengger: "unter dem ein und zwansigsten Breitengrade" in Paraguay. Of the samples available to me, those from Urucum, in western Brazil, are geographically nearest the type locality. North of Urucum, both in Brazil and Bolivia, two species of _Proechimys_ live together and one of them is the same species as that at Urucum. Of the two species found to the northward in Brazil and Bolivia, the one that ranges farther south probably will occur at the locality indicated by Rengger. Provisionally, therefore, the name _longicaudatus_ is allocated to the Urucum sample (see Osgood, 1944:198). In fact, the lack of a type specimen and the general nature of Rengger's description make "_Echimys longicaudatus_" a _nomen vanum_. If two species are found living together in the region of northern Paraguay indicated by Rengger it probably will be impossible to be sure to which one his vague description applies.

The form from Urucum, to which the name _Proechimys longicaudatus_ is here applied, is undoubtedly closely related to _Proechimys leucomystax_ Ribeiro, from Utiarití, on the Rio Papagaio and also to _P. roberti_ and _P. boimensis_, all from Brazil. _P. longicaudatus_ is used as the name of the species because it is the oldest of the four names.

=Proechimys longicaudatus brevicauda= (Günther)

_Echimys brevicauda_ Günther, 1 April 1877, Proc. Zool. Soc. London
for 1876, (49):748, fig. 9.

_Proechimys brevicauda_ Ihering, 1904, Rev. Mus. Paulista, S.
Paulo, 6:422; Osgood, 1914, Zool. Ser. Field Mus. Nat. Hist.,
10(12):168; Thomas, 1924, Ann. Mag. Nat. Hist., 13 (ser. 9):534;
Thomas, 1927, Ann. Mag. Nat. Hist., 19 (ser. 9):553; Thomas, 1927,
Ann. Mag. Nat. Hist., 20 (ser. 9):604; Thomas, 1928, Ann. Mag.
Nat. Hist., 2 (ser. 10):262; Thomas, 1928, Ann. Mag. Nat. Hist., 2
(ser. 10):292; Tate, 1935, Bull. Amer. Mus. Nat. Hist., 68
(5):399; Osgood, 1944, Zool. Ser. Field Mus. Nat. Hist., 29
(13):201.

_Proechimys cayennensis brevicauda_ Ellerman, 1940, The families
and genera of living rodents, Brit. Mus. (Nat. Hist.), 1:120.

_Type locality._--Chamicuros, Rio Huallaga, Peru. _Type_: British
Museum (Nat. Hist.), no. 69.3.31.7,[F]; _Lectoparatype_: British
Museum (Nat. Hist.), no. 66.1.29.8, from Upper Amazons (E.
Barttet), selected by Thomas (1900:301).

_Range._--Region of the headwaters and upper courses of the Juruá
and Ucaiali rivers, eastern Peru and northwestern Brazil.

_Diagnosis._--Upper parts Tawny and blackish without marked
longitudinal band on back; underparts buffy or white; aristiforms
narrow; skull slender; incisive foramen wide; vomerine sheath
complete; molariform teeth with three counterfolds, except p4 with
four and m3 with only two.

_Pelage._--_Aristiforms on middorsal region_: Blackish basally,
gradually blackening toward tip which is extended as a long
filament; total length, 18 to 20 mm; maximum width, 0.65 mm.
_Setiforms on middorsal region_: Gray basally, gradually
blackening toward tip but interrupted by Tawny, subapical zone 1.2
mm long; total length, 19 to 21 mm; maximum width, 0.1 mm.
_Setiforms on outer thighs_: Whitish basally, gradually blackening
toward tip but interrupted by Ochraceous-Tawny, subapical zone 3
mm long.

_Skull._--Slender but not elongated; nasals tapering posteriorly;
interparietals wide; supraorbital ridges not much extended and
faintly shown across parietals; jugals dorso-ventrally "wide" (3.5
mm); postorbital process of zygoma weakly developed; incisive
foramen 5.5 x 3 mm, oval, with posterior borders raised to form
ridges which extend toward premolars; vomerine sheath complete,
with maxillary part laterally compressed and extended toward
palate as ridge; mesopterygoid fossa extending forward as far as
third molars; bullae large and well inflated.

_Teeth._--Molariform teeth with three counterfolds, except p4
which has four and m3 which has only two counterfolds.

_Comparisons._--From _P. l. longicaudatus_, _brevicauda_ differs
in: upper parts Tawny instead of Ochraceous-Buff; lower premolar
with four instead of three counterfolds; m3 only, instead of both
m1 and m3, with two counterfolds. From _P. l. boimensis_,
_brevicauda_ differs in: upper parts Tawny instead of
Ochraceous-Orange; aristiforms wider; m3 with two instead of three
counterfolds.

_Specimens examined._--Total number, 3 (DZ), from Brazil, Amazonas,
_João Pessoa_, Rio Juruá.

=Proechimys longicaudatus boimensis= J. A. Allen

_Proechimys boimensis_ Allen, 24 July, 1916, Bull. Amer. Mus. Nat.
Hist., 35(27):523; Tate, 1935, Bull. Amer. Mus. Nat. Hist.,
68(5):400; Ellerman, 1940, The families and genera of living
rodents, Brit. Mus. (Nat. Hist.), 1:119.

_Proechimys cayennensis_ Osgood, 1944, Zool. Ser. Field Mus. Nat.
Hist., 29(13):199.

_Type locality._--Boim, Rio Tapajoz, Santarem, Pará, Brazil.
_Type_: American Museum of Natural History, no. 37486, adult male;
"October 10, 1911 (ex Museu Goeldi)."

_Range._--Along lower course of Tapajoz River.

_Diagnosis._--Upper parts Ochraceous-Orange; incisive foramen
posteriorly constricted; mesopterygoid fossa sharply pointed
anteriorly; p4 with four counterfolds, remaining molariform teeth
with three counterfolds.

_Pelage._--_Aristiforms on middorsal region_: Gray basally,
gradually blackening toward tip which is extended as a long
filament; total length, 16 to 18 mm; maximum width, 0.5 mm.
_Setiforms on middorsal region_: Gray basally, gradually
blackening toward tip, but interrupted by short (1.5 mm),
Ochraceous-Orange, subapical zone; total length 18 to 20 mm;
maximum width 0.09 mm. _Setiforms on outer thighs_: White basally,
gradually blackening toward tip but interrupted by
Ochraceous-Orange, or Ochraceous-Buff, subapical zone 3.5 mm long;
total length 15 to 17 mm; maximum width, 0.06 mm.

_Skull._--Elongate and slender; rostrum slender and long; nasals
evenly pointed posteriorly; supraorbital ridges weak and barely
reaching anteriormost part of parietals; zygomatic arches slender;
infraorbital foramen with groove for nerve-transmission obsolete;
postorbital process of zygoma weak and involving mostly squamosal;
incisive foramen 5 mm long and 2.5 to 3 mm wide, oval, with
margins not much extended caudad as ridges; posterior margin of
incisive foramen approximately 2 mm anterior to premolars;
vomerine sheath complete with maxillary part slender;
mesopterygoid fossa sharply pointed anteriorly and extending
forward as far as anterior part of third molar; bullae of medium
size, smooth and more or less triangular in contour.

_Teeth._--Crown length of upper molariform teeth 7 to 7.5 mm; all
upper molariform teeth with three counterfolds; lower premolar
with four counterfolds; lower molars with three counterfolds each.

_Comparisons._--From three of the other four subspecies found in
Brazil, _boimensis_ differs in having four, instead of three,
counterfolds in the lower premolars. Differences from _P. l.
brevicauda_ are indicated in the account of that subspecies.

_Remarks._--The material available from Boim, Tapajoz, is rather poor and of no great significance. The Museu Nacional has one specimen from Boim which agrees with the type in the American Museum of Natural History. The Museum of Comparative Zoology at Harvard College, however, has one specimen in its collection (MCZ no. 30888 [M]), adult, also from Boim, in which the color pattern is different although agreement with the type specimen is shown in cranial characters and width and length of hairs. This specimen is much darker than the other specimens (of orange-tint) assigned to this subspecies. However, in other samples of this species, similarly dark animals have been noted. It seems that the orange tint is gained only in old age. Another specimen (MCZ no. 30878 [F]) agrees in all respects with the type of the subspecies but the locality recorded on the label is Cametá, on the Tocantins River. Possibly the subspecies has a range so wide as to include Cametá but I suspect that the data on the label is incorrect as to locality. The collector marked [M] on the label although the specimen is a [F]. The mistake might have occurred through labeling of specimens at a time later than that at which they were collected. The collector was in both localities on more than one occasion.

_Specimens examined._--Total number, 5, from Brazil, Pará, as
follows: _Santarem_, Rio Tapajoz, Boim, 3 (AMNH type, MCZ 1, MN 1);
_Porto de Moz_, Tauarí, 1 (MCZ); _Cametá_ (?) 1 (MCZ).

=Proechimys longicaudatus longicaudatus= (Rengger)

_Echimys longicaudatus_ Rengger, 1830, Naturgeschichte der
Saeugethiere von Paraguay, p. 236.

_Loncheres myosuros_ Lichtenstein, 1832, Darstellung neuer oder
wenig bekannter Säugethiere, pl. 36 and text.

_Echimys myosuros Is._ Geoffroy Saint-Hilaire, 1840, Mag. Zool.,
Ann. 2 (ser. 2):15, 17; Allen, 1899, Bull. Amer. Mus. Nat. Hist.,
12(20):261.

_Echimys cayennensis_ Pictet, 1841, Mém. Soc. Phys. Hist. Nat.,
Genéve, 9:145; Waterhouse, 1848, Nat. Hist. Mammalia, 2:334.

_Proechimys longicaudatus_ Thomas, 1901, Ann. Mag. Nat. Hist., 8
(ser. 7):532; Thomas, 1904, Proc. Zool. Soc. London, p. 240;
Allen, 1916, Bull. Amer. Mus. Nat. Hist., 35(30):569; Tate, 1935,
Bull. Amer. Mus. Nat. Hist., 68(5):400.

_Proechimys cayennensis longicaudatus_ Ellerman, 1940, The
families and genera of living rodents, Brit. Mus. (Nat. Hist.),
1:121; Osgood, 1944, Zool. Ser. Field Mus. Nat. Hist, 29(13):198.

_Type locality._--Northern Paraguay ("unter dem ein und zwansigsten
Breitengrade"). _Type_: Apparently no type specimen was
preserved.

_Range._--Western Mato Grosso, Brazil, and northern Paraguay.

_Diagnosis._--Upper parts almost uniformly Ochraceous-Buff;
incisive foramen widest posteriorly; vomerine sheath complete; p4
and m2 with three counterfolds; m1 and m3 usually with two
counterfolds.

_Pelage._--_Aristiforms on middorsal region_: Dark gray, gradually
blackening toward tip that has long filament; total length 20 to
22 mm; maximum width 0.6 mm. _Setiforms on middorsal region_:
Whitish basally, gradually blackening toward tip but interrupted
by Ochraceous-Buff, subapical zone; blackish tip extended (3.5 mm)
and thin; total length 19 to 20 mm; maximum width 0.06 mm.
_Setiforms on outer thighs_: Whitish basally, progressively
grayish or blackish toward tip but interrupted by Light
Ochraceous-Buff or Ochraceous-Buff, subapical zone; total length
18 to 20 mm; maximum width 0.06 mm.

_Skull._--Slender; supraorbital ridge notably raised; bullae
large, elongate, smooth and inflated; jugals narrow; postorbital
process of zygoma of medium size and constructed entirely of
jugal; incisive foramen wide and large (5.5 x 3 mm), being
wider posteriorly than anteriorly and with posterior margins
raised; vomerine sheath complete, maxillary part slender
and laterally flattened; mesopterygoid fossa extending forward as
far as centers, or anterior margins, of third molars; posterior
palatine foramina on plane with posterior faces, or centers, of
second molars.

_Teeth._--Upper molariform teeth always with three counterfolds.
Lower molariform teeth: p4 and m2 always with three counterfolds,
sometimes the two anterior ones coalesced in m2; m1 with three
counterfolds in one specimen (33 per cent); m3 with only two
counterfolds in all specimens.

_Comparisons._--Differences from _P. l. leucomystax_ and _P. l.
roberti_ are given in the accounts of those subspecies.

_Specimens examined._--Total number, 3 (2 AMNH, 1 CNHM), from
Brazil, Mato Grosso, _Corumbá_, Urucum.

=Proechimys longicaudatus leucomystax= Ribeiro

_Proechimys leucomystax_ Ribeiro, May, 1914, Commissão de linhas
telegraphicas estrategicas de Matto Grosso ao Amazonas, Annexo no.
5. Hit. Nat., Zool., Mammiferos, p. 42, pl. 24 (orig. descr.);
Tate, 1935, Bull. Amer. Mus. Nat. Hist., 68(5):400; Ellerman, 1940,
The families and genera of living rodents, Brit. Mus. (Nat. Hist.),
1:119.

_Type locality._--Utiarití, Rio Papagaio, Diamantion, Mato Grosso,
Brazil. _Type_: Museu Nacional, no. 2212, adult, skull only,
collected on 5 May 1909, by Prof. A. Miaranda Ribeiro, is here
designated _lectotype_. See remarks.

_Range._--Serra dos Parecís, Mato Grosso, Brazil.

_Diagnosis._--Ochraceous-Buff, richly lined with blackish, on
upper parts; some setiforms completely blackened distally;
incisive foramen regularly ovoid; vomerine sheath incomplete;
upper molariform teeth and lower premolar with three counterfolds;
m2 with three counterfolds but m1 and m3 usually with two
counterfolds.

_Pelage._--_Aristiforms on middorsal region_: Grayish basally,
gradually blackening toward tip which is extended as a long
filament; total length 21 to 22 mm; maximum width 0.65 mm.
_Setiforms on middorsal region_: Whitish basally, gradually
blackening toward tip but interrupted by Ochraceous-Buff,
subapical zone; some setiforms grayish basally and gradually
blackening toward distal portion without any colored, subapical
zone; total length 20 to 22 mm, maximum width 0.06 mm. _Setiforms
on outer thigh_: White basally, gradually becoming gray toward tip
but interrupted by Light Ochraceous-Buff, subapical zone; some
setiforms gray basally and blackening toward tip, but interrupted
by Ochraceous-Buff, subapical zone; total length 15 to 18 mm;
maximum width 0.08 mm.

_Skull._--Slender; supraorbital ridges conspicuous; bullae large,
smooth and inflated, with slight, transverse groove; jugals
narrow; postorbital processes of zygomata small and involving only
squamosal; incisive foramen of medium size but narrow (5 x 2.5
mm), regularly oval and with margins uplifted posteriorly;
vomerine sheath incomplete but maxillary part projecting forward
and sometimes almost reaching premaxillary part; mesopterygoid
fossa reaching forward as far as centers of third molars;
posterior palatine foramina at plane of posterior faces of second
molars or slightly anterior thereto.

_Teeth._--Upper molariform teeth with three counterfolds. Lower
molariform teeth: p4 and m2 always with 3 counterfolds; m1 and m3
with 2 counterfolds.

_Comparisons._--From _P. l. longicaudatus_, _leucomystax_ differs
in: upper parts richly lined, instead of scarcely lined, with
blackish; incisive foramen narrower, and regularly oval instead of
widest anteriorly.

_Remarks._--_Proechimys leucomystax_ was described mainly on the
basis of the Utiarití specimen, here designated lectotype of the
species. The specimen from the Juina River is younger, as stated
by Ribeiro in his description. Ribeiro mentions the skin of the
specimen from Utiarití as "em muito mao estado" and I presume it
was discarded as it has not been found in the collection of the
Museu Nacional, Brazil.

_Specimens examined._--Total number, 6, from Brazil, Mato Grosso:
Cáceres, Salto Sepotube, 2 (MN); Cáceres, Tapirapoã, Rio Sepotuba,
2 (AMNH); _Diamantino_, Utiarití, Rio Papagaio, 1 skull (MN);
_Diamantino_, Rio Juina, 1 (MN).

=Proechimys longicaudatus roberti= Thomas

_Proechimys roberti_ Thomas, December, 1901, Ann. Mag. Nat. Hist.,
8 (ser. 7):531 (orig. descr.); Thomas, 1904, Ann. Mag. Nat. Hist.,
14 (ser. 7):195; Thomas, 1921, Ann. Mag. Nat. Hist., 8 (ser.
9):140; Tate, 1935, Bull. Amer. Mus. Nat. Hist., 68(5):400.

_Proechimys cayennensis roberti_ Ellerman, 1940, The families and
genera of living rodents, Brit. Mus. (Nat. Hist.), 1:121.

_Type locality._--Rio Jordão, _Araguarí_, Minas Gerais, Brazil; 960
meters alt. _Type_: British Museum (Nat. Hist.), no. 1.11.3.62, old
male, collected 8 August, 1902, by A. Robert; original number, 705.

_Range._--Western Minas Gerais and southern Goiaz.

_Diagnosis._--Color almost uniformly Ochraceous-Orange on upper
parts; setiforms long and narrow; incisive foramen long and wide;
vomerine sheath usually complete; upper molariform teeth and lower
premolar with three counterfolds; m3 with two, and m1 and m2 with
two or three, counterfolds.

_Pelage._--_Aristiforms on middorsal region_: Whitish basally,
gradually blackening toward tip; total length, 21 to 23 mm;
maximum width, 0.6 mm. _Setiforms on middorsal region_: Whitish on
basal half, gradually blackening toward tip but interrupted by an
Ochraceous-Orange, subapical zone 6 to 7 mm long; total length 25
to 30 mm; maximum width, 0.05 mm. _Setiforms on outer thighs_:
Whitish on basal half, gradually becoming gray and then blackish
toward tip but interrupted by wide, Ochraceous-Buff, subapical
zone, the tip being brownish or blackish; total length, 22 to 23
mm; maximum width, 0.04 mm.

_Skull._--Slender; supraorbital ridges bent outward and making
sharp angle at point of frontosquamosal suture, then continuing
backward parallel to each other and extending across parietals;
squamosal taking small part in supraorbital ridges; bullae large
(11 x 8 mm), inflated, with shallow depressions; incisive foramen
not especially long but wide (5 x 3 to 3.5 mm), widest in anterior
third and constricted posteriorly; vomerine sheath usually
complete, with maxillary part reduced to slender threadlike
process or, less commonly, missing; mesopterygoid fossa extending
forward as far as centers of third molars; zygomatic arches strong
with jugals of medium dorsoventral width (approximately 3.5 mm);
postorbital process of zygoma weakly developed and involving only
squamosal; posterior palatine foramina on plane of posterior
margins of first molars or slightly anterior thereto.

_Teeth._--Upper molariform teeth usually with three counterfolds
(92.5 per cent of 42 specimens); M2 with four counterfolds in 5 per
cent of specimens; M3 with two counterfolds in 2.5 per cent of
specimens. Lower molariform teeth: p4 usually with three
counterfolds (97.5 per cent of 39 specimens); rarely with four (2.5
per cent); m1 with three counterfolds in 58 per cent and two
counterfolds in 42 per cent of specimens; m2 with three
counterfolds in 61 per cent and two counterfolds in 39 per cent of
specimens; m3 always with only two counterfolds.

_Comparisons._--From _P. l. boimensis_, _roberti_ differs in: wider
incisive foramen; lower premolar with three, and one or two lower
molars with only two, counterfolds, instead of lower premolar with
four and all lower molars with three counterfolds. From _P.
longicaudatus_, _roberti_ differs in: upper parts Ochraceous-Orange
instead of Ochraceous-Buff; incisive foramen wider in posterior
third than in anterior third.

_Remarks._--This subspecies seems to be adapted to forests of post-climactic conditions which is probably typical of most valleys and margins of the rivers in southern Goiaz and western Minas Gerais. It was found in Goiaz usually in riparian forests with climactic associations or in some advanced stage of the sere. The animals also make incursions into nearby open areas or crops of corn.

_Specimens examined._--Total number, 52, from Brazil, as follows:
Minas Gerais, _Araguarí_, Rio Jordão (effluent of Parnaiba), 960
meters alt., 2 (1 CNHM, 1 DZ); Goiaz, _Anapolis_, 1010 meters alt.,
38 (MN); Goiaz, _Pouso Alto_, 768 meters alt., 11 (MN); Goiaz, Tio
São Miguel, 2 (MN).

=Proechimys guyannensis= (E. Geoffroy)

_Mus guyannensis_ E. Geoffroy Saint-Hilaire, 1803, Catalogue des
mammifères du Museum d'Histoire Naturelle, Paris, p. 194.

_Echimys cayennensis_ Desmarest, 1817, Nouv. Dict. Hist. Nat.,
Paris, nouv. ed., 10:59.

_Proechimys cayennensis_ Allen, 1899, Bull. Amer. Mus. Nat. Hist.,
12(20):261, 264; Tate, 1935, Bull. Amer. Mus. Nat. Hist.,
68(5):399; Ellerman, 1940, The families and genera of living
rodents, Brit. Mus. (Nat. Hist.), 1:120.

_General characters._--Size medium to large; tail usually short;
aristiforms narrow to wide; general color of setiforms on back
ranging from Tawny to Ochraceous-Buff and becoming gradually
lighter on sides; no conspicuous dark longitudinal band on back;
upper parts of hands and feet white to light brown; underparts
white, including inner sides of legs; skull elongate and not
conspicuously ridged; vomerine sheath complete or incomplete; upper
premolar with three counterfolds and molars with two or three;
lower premolar with three or four counterfolds, and lower molars
with two or three.

=Proechimys guyannensis villicauda= subspecies nova

_Type locality._--Tapirapoã, Rio Sepotuba, _Cáceres_, Mato Grosso,
Brazil. _Type_: Museu Nacional, no. 1932, adult male (color faded);
collected on 2 February, 1909, by Prof. A. Miranda Ribeiro;
original number, 788 A.

_Range._--Serra dos Parecís, headwaters of Paraguai and Tapajoz
rivers.

_Diagnosis._--Aristiforms wide and stiff; general color on upper
parts Ochraceous-Orange; incisive foramen long; vomerine sheath
incomplete or complete; lower premolar with four counterfolds,
remaining molariform teeth with three counterfolds.

_Pelage._--_Aristiforms on middorsal region_: Whitish basally,
gradually becoming gray toward tip, with distal fourth blackish
and ending as a long filament; total length, 22 to 23 mm; maximum
width, 1 mm. _Setiforms on middorsal region_: Whitish on basal
half, gradually blackening toward tip but interrupted by
Ochraceous-Orange, subapical zone 5 mm long; total length, 26 to
30 mm; width, 0.04 to 0.12 mm. _Setiforms on outer thighs_: Whitish
on basal half, gradually blackening toward tip but interrupted by
Ochraceous-Buff to Ochraceous-Orange subapical zone; total length
20 to 23 mm; width, 0.03 to 0.18 mm.

_Skull._--Strong; supraorbital ridges raised and extending across
anterior fourth of parietals; nasals elongate; bullae rounded,
inflated, with shallow grooves; postorbital process of zygoma
weakly developed and constructed entirely of jugal; incisive
foramen elongate and narrow (5.5 x 2.5 mm), posteriorly constricted
with posterior margins elevated above surface of bones; vomerine
sheath incomplete or complete but, when complete, with maxillary
part filiform and delicate; mesopterygoid fossa extending forward
as far as middle, or even anterior, parts of third molars;
posterior palatine foramina on plane of centers, or even anterior
faces, of second molars.

_Teeth._--Upper molariform teeth with three counterfolds. Lower
molariform teeth: premolar with four counterfolds, molars with
three counterfolds, sometimes with two folds coalesced in center
of tooth.

_Comparison._--From _P. g. ribeiroi_, and _P. g. bolivianus_,
_villicauda_ differs in wider aristiforms. From _P. g. ribeiroi_,
_villicauda_ further differs in: larger and wider incisive
foramen; vomerine sheath incomplete or complete instead of always
complete and thick. From _P. g. bolivianus_, _villicauda_ differs
in: lower premolars always, instead of rarely, with four
counterfolds, and m3 always with three counterfolds instead of
usually with only two counterfolds.

_Specimens examined._--Total number, 4, from Brazil, Mato Grosso,
as follows: _Cáceres_, Tapirapoã, 3 (MN); _Diamantino_, Rio
Papagaio, Utiarití, 1 (AMNH).

=Proechimys guyannensis ribeiroi= subspecies nova