Chapter I: Part 1

Speciation in the Brazilian Spiny Rats
(Genus Proechimys, Family Echimyidae)

BY
JOÃO MOOJEN

University of Kansas Publications
Museum of Natural History

Volume 1, No. 19, pp. 301-406, 140 figures in text
December 10, 1948

University of Kansas
LAWRENCE
1948

UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors: E. Raymond Hall, Chairman, A. Byron Leonard,
Edward H. Taylor

Volume 1, No. 19, pp. 301-406, 1 plate, 140 figures in text

Published December 10, 1948

UNIVERSITY OF KANSAS
Lawrence, Kansas

PRINTED BY
FERD VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS
1948

22-3343

Speciation in the Brazilian Spiny Rats
(Genus Proechimys, Family Echimyidae)

By
JOÃO MOOJEN

CONTENTS

PAGE
INTRODUCTION 305

METHODS AND TERMINOLOGY 305

ACKNOWLEDGMENTS 308

PALEONTOLOGY 308

SPECIATION 311
Subgeneric variation 312
Specific variation in the subgenus _Proechimys_ 314
Subspecific variation in the subgenus _Proechimys_ 317
Specific variation in the subgenus _Trinomys_ 320
Subspecific variation in the subgenus _Trinomys_ 322

TAXONOMIC CHARACTERS 323
Size and proportions of external parts 323
Pelage 324
Skull 326
Incisive foramen 326
Teeth 327

HABITS 330

CHANGES WITH AGE 331

Genus PROECHIMYS 333

ARTIFICIAL KEY TO SUBGENERA AND SPECIES 334

Subgenus PROECHIMYS 338
_Proechimys goeldii_ 338
_Proechimys goeldii steerei_ 338
_Proechimys goeldii goeldii_ 340
_Proechimys semispinosus_ 342
_Proechimys semispinosus liminalis_ 343
_Proechimys semispinosus amphichoricus_ 344
_Proechimys semispinosus kermiti_ 345
_Proechimys longicaudatus_ 346
_Proechimys longicaudatus brevicauda_ 349
_Proechimys longicaudatus boimensis_ 350
_Proechimys longicaudatus longicaudatus_ 351
_Proechimys longicaudatus leucomystax_ 352
_Proechimys longicaudatus roberti_ 353
_Proechimys guyannensis_ 355
_Proechimys guyannensis villicauda_ 355
_Proechimys guyannensis ribeiroi_ 361
_Proechimys guyannensis hyleae_ 361
_Proechimys guyannensis nesiotes_ 363
_Proechimys guyannensis leioprimna_ 364
_Proechimys guyannensis oris_ 365
_Proechimys guyannensis arescens_ 366
_Proechimys guyannensis riparum_ 367
_Proechimys guyannensis arabupu_ 369

Subgenus TRINOMYS 369
_Proechimys dimidiatus_ 371
_Proechimys iheringi_ 373
_Proechimys iheringi iheringi_ 378
_Proechimys iheringi bonafidei_ 378
_Proechimys iheringi gratiosus_ 379
_Proechimys iheringi panema_ 380
_Proechimys iheringi denigratus_ 381
_Proechimys iheringi paratus_ 382
_Proechimys setosus_ 384
_Proechimys setosus setosus_ 385
_Proechimys setosus elegans_ 387
_Proechimys albispinus_ 388
_Proechimys albispinus albispinus_ 390
_Proechimys albispinus sertonius_ 391

INCERTA SEDIS 392
_Proechimys myosuros_ 392

CONCLUSIONS 393

TABLE OF MEASUREMENTS 395

LITERATURE CITED 400

INTRODUCTION

The spiny-rats included in the genus _Proechimys_ are common in almost every forest of South America above the Tropic of Capricorn, and in Central America northward to approximately 12° N, in Nicaragua. In size and proportions they are similar to the brown rat _Rattus norvegicus_ but actually they belong to a very different suborder of rodents--the Hystricomorpha. The hystricomorphs are represented in South America by a large variety of animals, of which capybaras, agoutis and cavies are common representatives.

The pelage of the spiny-rats has a large number of flattened, spinelike hairs, especially on the back. The color ranges through different tints and shades of reddish-brown more or less evenly distributed on the upper parts; the underparts are usually pure white, sharply contrasting with the brown color above. The tail is bicolored, brown above and white below.

The spiny-rats live in forests of different types, generally in the proximity of water. Shelter is usually procured under boulders, stumps or masses of roots. The reproductive rate is low; on the average, there are only two young per litter and only two litters per year.

Sixty-odd names have been given to species and subspecies of _Proechimys_ in the last hundred and fifty years and no serious revision of the taxonomy of the genus was undertaken in the last century. The purpose of the present work is to provide means of understanding species and subspecies within the genus and to describe the different kinds known to occur within the confines of Brazil.

METHODS AND TERMINOLOGY

PELAGE.--It was found advisable to use a standardized nomenclature
for hairs. The names here proposed are a choice of those used in
the literature, with the suffix "_form_" as an element of
uniformity. I feel that it would be advantageous if everyone
adopted a similar universal system in mammalogy.

The names listed below are used as nouns and are considered as
English versions which could easily be adapted to different
languages. These names may be complemented with adjectives as
needed. Examples are lanceolate aristiforms, spinous aristiforms,
and woolly setiforms.

_Aristiforms:_ The most conspicuously developed hairs in a
three-layered pelage or the corresponding hairs in a simpler
pelage. Names previously used for these hairs are: guard hair,
leithaar and jarre.

_Setiforms:_ Common to all species and most numerous throughout the
pelage; second in conspicuousness, being the dominant hairs in the
middle layer. Synonyms are: over hairs, grannenhaare and soies.

_Villiforms:_ The smallest hairs in the three-layered pelage.
Synonyms are: underfur, wollhaar and duvet.

_Vibrissiforms:_ The vibrissae proper, or any typically sensory
hair.

TEETH.--The tritubercular nomenclature was abandoned because of
overwhelming difficulties; more research on the Hystricomorpha is
certainly needed before the tritubercular nomenclature can be
applied with confidence. The following names are used for features
of the molariform teeth:

_Main fold:_ The inner or lingual fold in the upper molariform
teeth and outer or labial fold in the lower molariform teeth.

_Counterfold:_ Any outer or labial fold in the upper or any inner
or lingual fold in the lower molariform teeth.

For incisors Thomas (1921:141) is followed: _opisthodont_,
_orthodont_ and _proodont_ depending on the angle between the
exposed part of incisors and the ventral surface of the rostrum.

The capital letters P and M designate premolars and molars,
respectively, of the upper jaws; lower case letters p and m
designate corresponding teeth in the lower jaws.

MEASUREMENTS.--Measurements of skins were used only when provided
by the collector. The length of the hind-foot is intended to be
always _cum unguis_, but in a few instances it is impossible to be
sure whether the collector included the nail. Length of tail was
used only when the tail seemed not to be mutilated. Ear
measurements taken by collectors are scarce. In spite of the
apparent usefulness of length of ear, it was found to be
inadvisable to take the measurement on the dry skins.

The following measurements of the skull are used in the tables:

_Greatest length:_ From the anteriormost part of the nasals to the
posteriormost part of the supraoccipital.

_Condylo-incisive length:_ From the anterior face of one incisor,
at the alveolus, to the posteriormost part of the exoccipital
condyle of the same side.

_Zygomatic breadth:_ Maximum distance across zygomata in a plane
perpendicular to longitudinal axis of the skull.

_Length of nasals:_ Maximum length of one or both, whichever is
the greater.

_Interorbital constriction:_ Least width between the orbits on top
of the skull.

_Palatilar length:_ From the posterior face of an incisor, at the
alveolus, to the nearest part of the posterior edge of the
palatine bone.

_Crown length of cheekteeth:_ From the anterior border of P4 to
the posterior border of M3.

In the accounts of species, measurements of aristiforms and
setiforms are used. The hairs measured were taken from the
middorsal region and outer thighs, and the measurements are means.

All specimens of which measurements are here recorded, as for
example in the tables, are fully adult; each specimen shows some
wear on each of the four upper molariform teeth unless otherwise
indicated.

Capitalized color terms are after Ridgway "Color Standards and
Color Nomenclature," Washington, D. C., U. S. A., 1912. One
setiform was taken from the animal and placed over the rectangles
in Ridgway's charts and the examination made under a microscope
with low (×7) magnification and natural light. This method was
found to give the most satisfactory results.

The following abbreviations are used for names of institutions:

AMNH--American Museum of Natural History.
CNHM--Chicago Natural History Museum.
DZ--Departamento de Zoologia da Secretaria de Agricultura, São
Paulo, Brazil.
MCZ--Museum of Comparative Zoology at Harvard College.
MN--Museu Nacional, Brazil.
MZ--Museum of Zoology, University of Michigan.
SEPFA--Serviço de Estudos e Pesquisas sobre a Febre Amarela, Brazil.
USNM--United States National Museum.
UZM--Universitets Zoologiske Museum, Copenhagen.

ACKNOWLEDGMENTS

Approximately two thousand skins and skulls were assembled at the
Museum of Natural History, University of Kansas, through the
coöperation of the authorities in the various institutions of North
America, Brazil and Denmark, as listed immediately above. This
comprehensive material was used to obtain a more complete
understanding of the group, and for the loan of these specimens I
am extremely grateful to the authorities of each of the
institutions.

First of all I acknowledge the encouragement given me in the
_Proechimys_ project by Heloisa Alberto Torres, Director of the
Museu Nacional, Rio de Janeiro. I extend my thanks also to Stephen
D. Durrant, of the University of Utah, for helpful corrections in
the preparation of the manuscript; to Mrs. Virginia Cassell Unruh,
for the preparation of the drawings of the skulls; to Miss Alice
M. Bruce for assistance in drawing the maps; and to my daughter,
Julieta, for help in assembling data and for typing.

Dr. Remington Kellogg, Curator of Mammals in the United States
National Museum, and the late Dr. Wilfred H. Osgood, formerly
Curator Emeritus of the Department of Zoology in the Chicago
Natural History Museum, generously permitted me to use their
private lists of South American mammals. These lists contain much
unpublished data, as for example, proof, in Kellogg's list, that
_Proechimys guyannensis_ (E. Geoffroy Saint-Hilaire, 1803)
antedates _P. cayennensis_ (Desmarest, 1817). I register here my
gratitude to both these zoölogists and acknowledge other critical
assistance from Dr. Kellogg.

The John Simon Guggenheim Memorial Foundation awarded me a
fellowship for which I am deeply grateful. This expression of the
Foundation's interest in education and good neighborliness made
possible the completion of the present paper.

Finally I desire to express my deepest gratitude to Professor E.
Raymond Hall, Director of the Museum of Natural History and
Chairman of the Department of Zoology at the University of Kansas
whose untiring aid and guidance has enabled me to terminate this
study.

PALEONTOLOGY

The only known, significant, fossil _Proechimys_ comes from deposits in the limestone caves of Lagoa Santa, Minas Gerais, Brazil. These deposits, of Late Pleistocene or Recent age, were extensively studied by P. W. Lund and the results published in a series of French and Danish papers. F. Ameghino (1934:110) studied another fauna from a deposit of similar age in the cave of Iporanga, São Paulo, Brazil. _Proechimys_ is recorded in his account under the inclusive specific name _fuliginosus_.

The molariform teeth of the fossil described by Lund (1841:pl. 21, fig. 14) shows its close relationship to the living form _P. s._ _elegans_ (Lund) which still inhabits the same region. It belongs in the more specialized subgenus _Trinomys_ which seems to have been derived from _Proechimys_. _Trinomys_ has the main fold in the molars always greatly developed and the fold tends to set apart one lamina in the occlusal surface. The Lagoa Santa fossil, like some specimens of the living subspecies, has a small main fold in P4. However, the main fold is large in all upper molars and in the lower molariform teeth which are notably specialized in the extreme reduction of the number of counterfolds to only one.

One hypothesis concerning the evolution of the genus is that a more primitive group of _Proechimys_ lived in all of the Central Plateau of Brazil in the Pleistocene Time. The climatic conditions at that time might have been such as to support large forests but, since the Pleistocene, these climatic conditions may have changed from humid to the present drier conditions, which support the dominant, savanna, floral climax. Actually the extinct fauna from the caves includes animals which have disappeared from the area and now live only in more humid areas, as for example _Myocastor_, which has shifted to the lowlands to the west and south.

Possibly climatic changes were responsible for the faunal shift from the region that is now a plateau in Central Brazil. This climatic change may have resulted from the gradual uplift of the eastern part of the continent. This uplift prevents part of the trade winds which come from the east from carrying the same amount of moisture inland as they did previously. In fact, the Andean revolution, even if it occurred as late as Late Tertiary, would have had no perceptible influence on the amount of water precipitated on the more eastern parts of the continent. Oliveira and Leonardos (1943:617) point out that after a Cretaceous submersion of the central part of Brazil, there was a general uplift. The authors (_op. cit._:689) mention the presence of continental Cretaceous deposits in the Central Plateau of Brazil, in support of these changes, and state that "pelo menos em certas zonas do litoral a elevação do continente prolongou-se até o Pleistoceno."

Berry (1942:373) concluded, among other things, that there was a southward extension "in South America of equatorial floras in the lower Miocene," and (_op. cit._:372) that ... "east of the Andean Axis in the south temperate zone there was a normal mesophytic flora ... instead ... of present day large steppes."

My idea is that a tropical forest still covered the Central Plateau of Brazil in (early?) Pleistocene times and that populations of _Proechimys_ of a primitive type, similar to _P. g. steerei_, for example, lived in that extensive forest-climax. The gradual uplift of the plateau, however, gradually brought about drier conditions in this region. As a result a large cliseral change was initiated, which shifted the forest-climax to the more humid eastern escarpments and lowlands that were gradually being developed, while the savanna climax was being established on the plateau. Eventually the effect of the decreasing moisture was locally accentuated by the erosion of the sandstones (Oliveira and Leonardos, 1943:690) in northeastern Brazil, thus depriving it of a natural reservoir of rain water. An arid belt was developed which now constitutes an efficient geographic barrier to the distribution of many kinds of animals.

One marginal species may have shifted eastward with the forest-climax to effect the Recent distribution. The eastern species became completely isolated from the main group, accumulated mutations, and evolved into the subgeneric type _Trinomys_. The generic trend that gave rise to _Trinomys_ probably remained more stable as far as supraspecific changes are concerned. The lack of barriers in the distributional area of the original group favored the dispersal and submergence of mutations and, therefore, there was but little further supraspecific evolution. The speciation in both subgenera finally resulted from gradual differentiation of varying populations since they show combinations of the generic biotypes and possess few truly qualitative characters.

The cliseral changes in the Central Plateau, which developed the dry belt, a barrier, might explain the evolution of a few more supraspecific groups of mammals, as indicated by the presence of similar forms in the Amazonian region and in Southeastern Brazil. Among these _Echimys_ and _Phyllomys_, in the same family with _Proechimys_, show differences that are parallel to those observed in _Proechimys_. One of these parallel changes is the increased lamination of the cheekteeth. Although _Echimys_, from the Amazonian region, has upper molariform teeth with the four laminae fused, _Phyllomys_ has the four laminae completely separated.

None of the genera known from the Upper Oligocene and Miocene of Argentine deposits seems to be directly ancestral to _Proechimys_.

SPECIATION

The detection of differences of systematic worth between populations of animals, represented by skins and skulls, is a step preliminary to deducing the factors responsible for the differences. Ordinarily the factors which cause heritable differences have to do with geographic isolation and adaptation to ecological conditions. When differences in the structure of the animal are known, a person is led to speculate on the factors which could cause them. For one thing, does the observed degree of difference tend to isolate animals possessing the "new" character from the other animals? It would seem to me that the isolation once started by one of these differences tends to be accentuated with time and the difference itself thus then becomes a factor responsible for further differentiation.

Whether or not transition from one character to another occurs gradually, in its geographic expression, and thus whether or not intergradation occurs between two subspecies, can be ascertained by the analysis of a series of population-samples appropriately distributed geographically. If two characters of systematic worth are known to blend in one part of the geographic range of a subgenus, and if the same two characters are seen in two other populations, far removed geographically from each other and without any samples of annectent populations to provide actual evidence of intergradation, then such intergradation is to be inferred.

The available collections of _Proechimys_ mostly were made haphazardly with the result that there are extensive areas from which no specimens as yet are available. Thus, actual proof of intergradation is often lacking in areas where it almost certainly occurs. In some extensive areas, however, many samples, from relatively regular intervals, have been available and they provide genuine proof of intergradation. These instances have served as a guide for estimating whether other samples should be considered to be full species or instead merely subspecies of the same species.

Lack of intergradation in any of the characters may be accepted as the criterion of full species. Where two populations occupying the same range (sympatric populations) show different qualitative characters, they almost certainly do not crossbreed. Furthermore the characters that distinguish such kinds of nonintergrading animals are likely to be considered as of full specific value when detected in far distant parts of the range of the subgenus.

In a genus that is widespread and continuously distributed, it is useful to know which characters always distinguish full species and which ones, sometimes or always, distinguish only subspecies, since in a population from a small island, there is, ordinarily, less individual variation than in a corresponding population from the mainland or a larger island; under certain circumstances a person might be tempted to give specific rank to the population when its characters actually are analogous to those separating subspecies elsewhere.

Sometimes it is convenient to recognize species-groups, a systematic category without nomenclatural status, intermediate between the species and the subgenus. When there are two groups of species not sharply separated, including one species whose characters overlap those of each of the two groups, it would seem most appropriate to recognize only species-groups instead of subgenera. When, on the other hand, the two groups of species have mutually exclusive characters and a species with intermediate characters is unknown, the two groups of species can conveniently be accorded separate subgeneric rank.

SUBGENERIC VARIATION

A few characters are common to one group of species and other features are common to a second group. The most striking of these features is the character of the main fold in the molariform teeth. In one group the fold transversely crosses the crown of the tooth and in the other it extends scarcely halfway across. No specimen is intermediate in this respect. These two groups, furthermore, are separated geographically by an important barrier, the arid belt that starts in the northeastern littoral of Brazil (Ceará), and that extends south and southwesterly, more or less accompanying the São Francisco River in the Plateau, to about 20° S. _Proechimys_ is thought not to inhabit this arid belt. At the latitude of 20° S the conditions become more suitable for _Proechimys_, especially along the rivers which flow eastward, but there the Plateau is replaced by mountains: the Serra Geral at the west, and Serra da Mantiqueira at the south; these ranges are bare of forests at higher elevations. Two groups of species of _Proechimys_ are, therefore, kept geographically isolated: one group lives in southeastern Brazil, and the other lives in a large area to the west which starts at 21° S in Paraguay and Brazil and widens northward and includes, farther west, central and northern Brazil and all the South American countries above 21° S, as well as Central America northward to southern Nicaragua.

The two groups which are here treated as subgenera may be designated as follows:

_Trinomys_--main fold deep: aristiforms well-developed on the rump and outer thighs; tail no less than 75 per cent of length of head and body; skull without ridges across the parietals; no conspicuous groove for transmission of nerve inside infraorbital foramen; molariform teeth decreasing in size from premolar to third molar; 1 to 3 counterfolds in the molariform teeth.

_Proechimys_--main fold shallow: aristiforms not developed on rump and outer thighs; tail less than 75 per cent of length of head and body; groove for transmission of nerve present in infraorbital foramen of several subspecies; molariform teeth increasing in size from premolar to second molar; 2 to 5 counterfolds in molariform teeth.

Most of these characters vary but do not overlap. Subgeneric rank is here accorded to the two groups of _Proechimys_ characterized immediately above.

The primary cause of the subgeneric differentiation is thought to have been geologic changes in the continental area. As already pointed out (see Paleontology), decreasing humidity in the Central Plateau of Brazil may have caused a migration southwestward of one or more of the species along with the forests. Once isolated geographically, the species probably differentiated at an accelerated rate.

The fact that a much larger number of subspecies occupies the larger geographic range of the subgenus _Proechimys_ would not be sufficient to prove that this subgenus, _Proechimys_, is nearer to the primitive group than _Trinomys_, the subgenus occupying the smaller range with fewer subspecies. The paleontological evolution of the rodents, however, consistently points to teeth with a larger number of counterfolds (as seen in _Proechimys_) as the primitive condition. The extension of the main fold, tending to set apart one lamina in each upper molariform tooth, seems to be a specialization; reduction in the size of the head and body, increase in length of tail and decreasing size of molars posteriorly also may be specializations. The main point, however, is to establish if _Trinomys_ is a relic group rather than a "differentiated" one. If an intermediate form were known which connected _Trinomys_ with one species of _Proechimys_ more than with another or even if _Trinomys_ itself more closely resembled one of the groups of species of the subgenus _Proechimys_ than it did another, we would assume that divergence and selection accounted for the subgeneric variation. The lack of any such connecting link favors the first idea, namely that _Trinomys_ differentiated rapidly with the aid of geographic variation.

If _Trinomys_ is, as I am inclined to consider it, the result of "differentiation," its subgeneric features are to be admitted as "new" and therefore the most primitive species in the genus should be found in the subgenus _Proechimys_.

It is a matter of common sense to admit the two groups considered above as subgenera rather than genera. Since the two structural plans were established they would, and do, act as different sources of variation. On the other hand, the morphological differences do not give the two groups an amount of morphological differences that would justify full generic rank for each.

SPECIFIC VARIATION IN THE SUBGENUS PROECHIMYS

Most of the described forms in the subgenus were initially named as distinct full species. More recently, however, in accordance with the ideas now prevalent in systematic work, many of the named kinds were reduced to the rank of subspecies. Tate first made a geographic arrangement (1935:399-400) and later (1939:177-178) provisionally synonymised several named kinds of _Proechimys_ with _Proechimys_ "_cayennensis cayennensis_." A similar tendency was clearly displayed by Ellerman (1940:115-122) who allocated 29 names, out of 33 (in the subgenus, as here understood), to the species _Proechimys guyannensis_ and gave full specific rank to four other named kinds. Osgood (1944) also had the same viewpoint; that is to say, he appeared to have the idea that there were only two full species in the subgenus in Brazil--admitting this orally--and consequently he synonymised some full species where two or more occurred in the same place, thinking that he was dealing with individual, rather than specific, differences. Evidently the number of species in the subgenus cannot be great because the known kinds show few patterns worthy of specific designation and therefore the majority of the existing names should be suspected of having no more than subspecific value. Nevertheless none of the above writers presented real evidence in support of his arrangement.

Criteria for the recognition of full species are most easily recognized where two or more different species live together. In the literature, _P. goeldii_ and _P. "oris"_ were mentioned by Thomas (1912:89) as having been collected in the same place; _P. mincae_ and _P. canicollis_, by H. H. Smith (in Allen, 1904:440); _P._ "_leucomystax_," from Utiarití, by Miranda Ribeiro (1914:42) and _P._ "_longicaudatus_," from the same place, by Allen (1916:569) were other examples. In these, and other alleged instances of two or more kinds occurring together, detailed study of the specimens concerned was necessary to learn the true facts. Also with the opportunity to compare collections from several different places, new facts emerged. _P. longicaudatus_, as it was conceived of by Allen, was a composite species, but in one locality, Utiarití, Ribeiro and Allen actually were dealing with two distinct species.

The species, or subspecies belonging to different species, living together are: _goeldii_ and _hyleae_, at Fazenda Paraiso; _goeldii_ and _riparum_ in Manaus; _boimensis_ and _hyleae_ in Tauarí; _leucomystax_ and _villicauda_ in Utiarití; _mincae_ and _canicollis_ in Bonda; _gularis_ and _hendeei_ on the banks of Rio Napo ("same trap lines," according to P. Hershkovitz, _In Litt._). Study of samples of the above named pairs of kinds of _Proechimys_ showed the following specific differences: _goeldii_ is large with narrow aristiforms, has a large and strongly built skull, with four counterfolds in one or more upper molars: _hyleae_ is smaller, has wide aristiforms, smaller skull with less pronounced ridges, and never has more than three counterfolds in the upper molariform teeth; _riparum_ closely resembles _hyleae_; _boimensis_ has thin aristiforms, small skull and no more than three counterfolds in the upper molariform teeth in contrast to _hyleae_, already discussed; _leucomystax_ closely resembles _boimensis_; _villicauda_ closely resembles both _hyleae_ and _riparum_; _mincae_ is similar to _hyleae-riparum-villicauda_; _canicollis_ has the number of counterfolds in all molars reduced to two; _gularis_ is large, has a strongly built and ridged skull, some upper molariform teeth with four counterfolds and wide aristiforms; _hendeei_ closely resembles _leucomystax_ and _boimensis_.

The evidence obtained from study of specimens where two or more species occurred together was applied to the remaining samples and the geographic distribution was worked out. As a result the arrangement below was made, including all valid kinds already named and those here newly named from Brazil. The names of kinds I do not consider as belonging to the subgenus (and genus) are excluded. These are _Echimys macrourus_ Jentink, not seen, and _Proechimys cayennensis hoplomyoides_ Tate (= genus _Hoplomys_). The application of names is tentative, however, because the types deposited in Europe have not been seen. An asterisk denotes the forms not seen by me.

_Proechimys guyannensis: arabupu, arescens, bolivianus, cherriei,
chrysaeolus, guairae, o'connelli, guyannensis*, hyleae, leioprimna,
mincae, nesiotes, ochraceus, oris, poliopus, ribeiroi, riparum,
trinitatis, urichi, vacillator*, villicauda, warreni._

_Proechimys longicaudatus: boimensis, brevicauda, elassopus,
hendeei, leucomystax, longicaudatus, nigrofulvus, pachita,
rattinus*, roberti, securus, simonsi._

_Proechimys semispinosus: amphichoricus, burrus, calidior,
centralis, chiriquinus, colombianus, decumanus, goldmani*,
gorgonae, gularis, hilda*, ignotus, kermiti, liminalis,
panamensis, rosa*, rubellus, semispinosus._

_Proechimys goeldii: goeldii, steerei._

_Proechimys canicollis._

_Proechimys guyannensis_ appears to be more plastic than any other species. In size of animal, width of aristiforms, color and number of counterfolds in the cheekteeth, it shows marked response to variations in geographic conditions. _Proechimys longicaudatus_ is apparently less plastic; only the number of counterfolds shows marked variation. _Proechimys semispinosus_ varies much within its range. _Proechimys goeldii_ seems to be relatively uniform. _Proechimys canicollis_ shows relatively little variation throughout its range but probably is divisible into two or more subspecies.

The primitive _Proechimys_ probably was large with a short tail, narrow aristiforms, strongly built skull, and five counterfolds in each molariform tooth. Primitiveness here is inferred from characters which now are of general occurrence in the whole group as opposed to those restricted in geographic occurrence.

It is a curious fact that in this genus, populations from small islands are more primitive than populations on the mainland. Apparently a small population restricted to a small island tends to revert to the primitive type. The homozygous condition will tend toward a generalized genotype and the disappearance of secondary biotypes. _P. i. iheringi_ on the Island of São Sebastião averages larger, has thinner aristiforms, and a stronger skull than the same subspecies on the mainland, and the cheekteeth usually have two and three counterfolds. The same subspecies on the mainland has no more than two counterfolds. _Proechimys semispinosus gorgonae_ and _Proechimys semispinosus ignotus_, living on Gorgona and San José islands, respectively, are both characterized by large size, short tails, strong and conspicuously ridged skulls, and cheekteeth frequently with four and five counterfolds. On the mainland, closely related subspecies, like _P. s. panamensis_, _chiriquinus_ and _gularis_, far less frequently have four counterfolds in more than one or two teeth. More striking still is the population-sample of _gularis_ from the island of Llunchi, in the Rio Napo, eastern Ecuador. In it there is a higher ratio of cheekteeth with four counterfolds than there is in the samples from the banks of the river.

The two insular forms, _P. s. gorgonae_ and _P. s. ignotus_, referred to as primitive in the discussion above, have wide aristiforms, which is contrary to what would be expected in a primitive _Proechimys_. Supposing, however, as actually seems to be the fact, that narrowness of the aristiforms depends on an increased number of genes, we deduce that the population from the mainland, that gave rise to the populations of the islands, did not have all of the genes necessary to make the aristiforms narrow. In fact the subspecies known on the mainland, near the aforementioned islands, have wide aristiforms.

Another point which favors the idea that narrow aristiforms result from an increased number of genes is that, generally, the aristiforms are narrow in any species whose geographic range is extensive and relatively uniform.

_Proechimys goeldii_ is the species which has the largest number of characters that are judged to be primitive, and it may be the oldest stock. _P. semispinosus_, _P. longicaudatus_ and _P. guyannensis_ may have been derived from an early splitting of the genus or they may have branched off the main stem at different times. _P. canicollis_, however, seems clearly to be an offshoot of _P. guyannensis_; _canicollis_ shows greater resemblance to _guyannensis_ than to any other species. _P. g. vacillator_ is another close relative of _P. guyannensis_ with the number of counterfolds almost as much reduced as in _P. canicollis_. Conceivably, _vacillator_ is a full species, but the reduction in number of counterfolds in the teeth more probably expresses only one extreme of a gradient, as will be discussed below.

SUBSPECIFIC VARIATION IN THE SUBGENUS PROECHIMYS

In spite of the lack of specimens from areas in which _Proechimys_ certainly occurs, it is evident that the genus has great plasticity and that the number of subspecies will be greatly increased as additional material is studied. Only perfunctory examination of samples from outside the area of Brazil shows me that there are several unnamed subspecies there. My impression is that Allen's _trinitatis_, of Trinidad, the genotype of _Proechimys_, will eventually be split.

There are two main lines of subspeciation in _Proechimys guyannensis_. The one south of the Amazon River includes _P. g. bolivianus_, in Bolivia, _P. g. villicauda_, and _P. g. ribeiroi_ occurring on the divide of the headwaters of the Amazon and Parana rivers, in Brazil, and _P. g. hyleae_ in the lower Tapajoz and _P. g. nesiotes_ in the lower Tocantins. All six subspecies have a large number of counterfolds in the molariform teeth. In these six subspecies, p4 has four counterfolds and the lower molars have three each. Toward the northeastern coast the number of counterfolds decreases to three in p4 and to two in the lower molars, as in _P. g. arescens_, _P. g. leioprimna_ and _P. g. oris_.

In northern South America, north of the Amazon River, the subspecies with the greatest number of counterfolds is _P. guyannensis warreni_ (known from only the Demerara River area); p4 has four counterfolds and the lower molars have three each. The number decreases in all the adjacent populations: _P. g. guyannensis_, in the Guianas, _P. g. trinitatis_, and _P. g. urichi_ (going westward from the Guianas to Venezuela) have the counterfolds reduced to three in p4, but the lower molars still have the same number of counterfolds, namely, three, although there is a tendency for them to coalesce; farther west, on the coast, the number decreases to three counterfolds in p4 and to only two in the lower molars as in _P. g. guairae_ and _P. g. mincae_. Subspecies south of the coast show the same reduction of counterfolds, _P. g. cherriei_ and _P. g. o'connelli_ being examples; _P. g. ochraceus_ and _P. g. poliopus_ have the reduction carried to the upper molars, M3 having usually only two counterfolds; _P. g. chrysaeolus_ in the valley between the Madalena and the Cauca rivers seems to be somewhat isolated and shows reversion to three counterfolds in the lower molariform teeth; directly southward of the range of _P. g. warreni_ the number of counterfolds decreases to three in all lower cheekteeth (population at Ayan-Tepuy, southern Venezuela), and then to three in p4 and to two in the lower molars, as in _P. g. arabupu_ on the Brazilian side of Mount Roraima, and the reduction is extended to the upper molars in _P. g. vacillator_.

On the north bank of the Amazon, the only population of _P. g. hyleae_ known to me (from Obidos) has four counterfolds in p4 and three in the lower molars; _P. g. riparum_, from Manaus, also on the north bank of the Amazon, has three counterfolds in p4 and two counterfolds in the lower molars. _P. g. hyleae_ occurs also on the south bank of the Amazon. _P. g. riparum_, therefore, may be the northern part of the southern cline, instead of the southern end of the northern cline.

The whole picture, as outlined above, may be explained by assuming that the species _P. guyannensis_ differentiated somewhere on the Central Plateau of South America, with three counterfolds in each upper molariform tooth, four counterfolds in the lower premolar and three counterfolds in the lower molars. The species might have extended its range to the Guianas and then all the biotypes with reduced number of counterfolds might have slowly developed by natural selection. The gradient is, broadly, from subspecies with greater number of counterfolds in more humid areas, to a gradually lessening number of counterfolds in less humid areas.

_Proechimys longicaudatus_ is limited in the south to the headwaters of the Parana River drainage, where the subspecies _P. l. roberti_ and _P. l. longicaudatus_ are found. The species ranges northward through the Tapajoz drainage, with _P. l. leucomystax_ in the headwaters and _P. l. boimensis_ in the lower course. To the northwest and west the species is represented in Bolivia by _P. l. securus_; _P. l. elassopus_, _P. l. simonsi_, _P. l. pachita_, and _P. l. hendeei_ occur in Peru and _P. l. brevicauda_ in Peru and Brazil; and _P. l. nigrofulvus_ occurs in Ecuador. Again in _P. longicaudatus_ it seems that the number of counterfolds follows a gradient from more humid areas with four counterfolds in p4, as seen in _nigrofulvus_, _pachita_, _simonsi_, _elassopus_ and _brevicauda_, decreasing to three or four in _securus_, to three in _longicaudatus_, but with m3 having only two counterfolds in _leucomystax_ and _roberti_. _P. l. boimensis_, widely separated in the lower Tapajoz (no samples being known from the intervening range) may be the end of a cline started by _leucomystax_ with only 2 counterfolds in m3 and ending to the northward with four counterfolds in m3. Over the same area the counterfolds in p4 increase from 3 to 4.

Of _Proechimys goeldii_ I have had inadequate material but there seems to be a similar gradient in it which may be traced from _P. g. steerei_ to _P. g. goeldii_. _P. g. steerei_ has four counterfolds in more upper molars than occurs in the other subspecies.

_Proechimys semispinosus_ has its wide range in the mountainous, western area of South America, the headwaters of the Amazon drainage and northward in Central America and the nearby Pacific Islands. In these populations a gradient may exist in the number of counterfolds which is varied in every population. The highest number seems to occur in the populations from northern Peru and Ecuador, decreasing from there in all directions, except in the Panamanian and Columbian islands. In gross examination, it seems that the size of the animals increases to the northwards.

SPECIFIC VARIATION IN THE SUBGENUS TRINOMYS

Some specific characters are duplicated in each of the two subgenera; that is to say, there are some parallel developments and they give the common generic stock its biotypical variability. Among these parallel developments are the width of the aristiforms, the amount of pigment in the agouti-colored setiforms, and the shape of the nasal bones. Other characters, however, appear in one subgeneric group and not in the other. The specific variation will be discussed separately for each subgenus.

The aristiforms are narrow and soft in _P. dimidiatus_ and in the other species are wide and stiff, and on the outer thighs and rump some are light-colored. _P. albispinus_ has the maximum number of light-colored aristiforms; they are present over the sides and back. This species has, however, a type of aristiforms unique in the genus--the clavate type. The tail is longer in _P. iheringi_ and _P. setosus_ than in _P. dimidiatus_ and _P. albispinus_; the longer type is associated with a penicillate tip suggesting an adaptation to arboreal habit. The skull and nasals are longer in _P. dimidiatus_ and _P. iheringi_ than in _P. setosus_ and _P. albispinus_. In the latter two species the longitudinal dorsal outline of the skull is conspicuously convex as opposed to slightly convex in the other two species. The palate is longest in _P. dimidiatus_ and _P. iheringi_ extending posteriorly to the level of the second molars; it is slightly shorter in _P. setosus_ and shortest in _P. albispinus_ where it does not extend behind the level of the first molars. The incisors are opisthodont in _P. dimidiatus_ and _P. iheringi_ and orthodont in _P. setosus_ and _P. albispinus_ and even proodont in one part of the last species.

The molariform teeth have a large number of counterfolds in both _P. dimidiatus_ and _P. iheringi_, although the number varies but little in the first species and much in the second. The variation in _P. iheringi_ decreases in populations of increasingly more northern geographic distribution; in both _P. setosus_ and _P. albispinus_ the number of counterfolds is greatly reduced; there is only one in most specimens of _P. albispinus_. The incisive foramen is small and nearly round in _P. dimidiatus_, larger and elongate in _P. iheringi_, very narrow and fissurelike in both _P. setosus_ and _P. albispinus_.

The characters of _Trinomys_, as briefly outlined above, seem to be the result of one original species having split first into four species which provide a gradient for certain characters. Subsequently one of these four species, _P. iheringi_, split into six subspecies and another gradient, parallel to the first, and involving the same characters, is to be seen.

The interrelationship among the species is evident, not only because they have the same subgeneric characters, but because the full species themselves provide successive steps in a stairway of increasing specialization from _P. dimidiatus_ to _P. albispinus_.

Morphologically _P. dimidiatus_ and _P. iheringi_ are sometimes difficult to distinguish, especially on the basis of cranial features. Nevertheless close attention to the small, nearly round, incisive foramen of _P. dimidiatus_ versus the larger, more elongate foramen in _P. iheringi_ will permit separation of the two. However, the two species live in the same place and one is led to infer that there may be greater differences in their physiology than in their morphology. In fact Dr. H. W. Laemmert, from the Serviço de Estudos e Pesquisas Sobre a Febre Amarela in Brazil, informs me that while _P. dimidiatus_ was highly susceptible to the virus of yellow fever (18 out of 24 with virus in circulation), _P. iheringi_ showed a lower rate of susceptibility (3 out of 25 with virus in circulation). _P. longicaudatus roberti_, belonging in the other subgenus, showed no susceptibility at all.

At Teresópolis, Estado do Rio de Janeiro, the two species were found in two different forests, only a few kilometers apart, but _dimidiatus_ lived at a higher elevation, where the humidity was remarkably higher. Naturally the plant associations were different in the two forests. This seeming ecological adaptation of the two kinds of _Proechimys_ may explain why _P. iheringi_ ranges farther north; the forests to the northward are less humid.

One of the four species, _P. setosus_, subspecies _elegans_, was used by Winge (1941:80, 82) as representative of the genus _Proechimys_ when he was estimating the relationships of that genus. Because _Cercomys_, with four crests in each of its cheekteeth, was, on other grounds, regarded by him (_op. cit._: 80) as "... the most primitive genus within the group.", and because he noted in _P. s. elegans_ 4 crests in P4 and in some first molars, he concluded that _Proechimys_ was "very closely related to _Cercomys_." His conclusion seems to be correct, but actually other species of _Proechimys_ (subgenus _Trinomys_), for example, _P. dimidiatus_, have four or more crests in each cheektooth, and, therefore, may be considered as more closely related to _Cercomys_ than is _P. setosus_. If a large number of crests indicates primitiveness, _P. dimidiatus_, always with four, is more primitive than any other species in the subgenus _Trinomys_. Also, the large skull, long hind foot, short tail and thin aristiforms of _P. dimidiatus_, in my opinion, are primitive characters.

SUBSPECIFIC VARIATION IN THE SUBGENUS TRINOMYS

One of the species of _Trinomys_, _Proechimys iheringi_, is here subdivided into six subspecies which show a clinal variation. _P. i. iheringi_, in the southernmost part of the range of the species (Ilha de São Sebastião), has three counterfolds in the upper cheekteeth of almost every young specimen but one of these counterfolds, since it is small, very shallow, and disappears after little wear, is probably in the process of disappearance; all lower cheekteeth have two counterfolds or, rarely, m3 has only one. _P. i. bonafidei_ is the next subspecies northward, where it was collected at 850 m altitude (Fazenda Bõa Fé). This subspecies still has two counterfolds in all the upper cheekteeth; only 3 out of 16 specimens fail to have these counterfolds coalesced in one or more of the teeth. In the lower cheekteeth the coalescence is evident in 18 per cent of the specimens. _P. i. gratiosus_, from Floresta da Caixa Dagua (alt. 750 m), geographically is well removed from _bonafidei_ (more than two degrees north), and no samples were obtained from the intervening area. It shows such great reduction in the counterfolds that the existence of intermediate populations is clearly suggested. Every upper cheektooth of this subspecies has the two counterfolds coalesced and in 40 per cent of the specimens M3 has only one counterfold; in the lower cheekteeth 60 per cent of the specimens have only one counterfold in m3. _P. i. panema_, occurring approximately 100 kilometers to the northward of _P. i. gratiosus_ (lowland form), has one counterfold in M3 in only 20 per cent of the specimens but the lower third molar has only one counterfold in 80 per cent of the specimens. In _P. i. denigratus_, from about 3 degrees north of the range of _P. i. panema_, the reduction is proportionately greater: P4 now is the only upper cheektooth with two counterfolds in every specimen; all molars tend to have only one; p4 has also two counterfolds but all lower molars have only one.

The relative size of the tail also varies in a cline from south to north. Its length is approximately 87 per cent of the length of the head and body in _P. iheringi_; 88 per cent in _bonafidei_; 99 per cent in _gratiosus_; 100 per cent in _panema_; and 103 in _denigratus_.

One of the subspecies, _P. i. paratus_, however, seems to be completely out of the dental cline. It was collected in the near proximity of the type locality of _P. i. gratiosus_, at an elevation of 120 m lower. This subspecies has two counterfolds in all molariform teeth and only one of the two specimens known shows these counterfolds coalesced in P4 and M1. The sample, 2 specimens, is too small to be trustworthy; hence it is impossible satisfactorily to account for the break in the clinal variation. Conceivably two full species are involved, but I prefer at present to defer decision on this problem until such time as more evidence is accumulated.

_P. setosus_ is poorly represented, both of the available skins being faded. Furthermore, no type locality is known for the subspecies _P. s. setosus_.

_P. albispinus_ has only two known subspecies: _P. a. albispinus_, living in a region of higher humidity, is slightly the darker and has subapical zones of the setiforms on the sides Ochraceous-Tawny; _P. a. sertonius_, living in a much drier region, has the same subapical zone Ochraceous-Buff. The number of specimens of _P. a. sertonius_ is so few that no gradient can be detected, even if one exists.

TAXONOMIC CHARACTERS

Size and Proportions of External Parts

Absolute size of head and body, tail, hind-foot and ear are useful in distinguishing subgenera and subspecies and to some extent in differentiating species.

The length of head and body is large to medium in _Proechimys_ and medium to small in _Trinomys_. The tail is long to medium in _Trinomys_ and short in _Proechimys_. The longest tail, 242 mm, is found in _P. i. denigratus_, and the shortest tail, 123 mm, in _P. g. steerei_. The relative length of tail also provides gradients or clines.

In every species, males surpass females in average size. Nevertheless, the largest animals are usually females. How this paradoxal fact is to be accounted for, I am not sure, but it may be that the animals grow as long as they live and that females have more chances to survive longer since the care of the young keeps them closer to shelter.

_Color._--Upper parts vary from Buckthorn Brown to Ochraceous-Buff. Dark color ordinarily is correlated with an environment of higher degree of humidity and light color with lower humidity. However, species may be found in similar conditions of humidity but differing in color. _Proechimys albispinus albispinus_, for example, a light-colored form, is found in areas where the rainfall averages 1,000 to 1,500 mm of annual precipitation, in the isohygra of 80 per cent relative humidity. These conditions actually are similar to those where _P. dimidiatus_, of darker color, is found. The subspecies _albispinus_, however, ranges mostly over a dry area and the fact that it occurs also in a moist area without appreciable change in color is difficult to explain.

Insular populations are usually darker or richer in color than corresponding continental populations. On a small island, uniformity of environment and inbreeding may be responsible for an accumulation of characters for richness of color.

Pelage

The pelage provides most useful taxonomic characters. Excepting the vibrissiform hairs, all of the elements of the pelage have a common feature, the flattened shape. The hair constellation (_cf._ Toldt, 1935) on the upper and lateral surfaces is composed of hairs of two main types: _aristiforms_ (guard hairs) and _setiforms_ (over hairs).

The aristiforms are wide, strong, and have the dorsal (= anterior) margins raised, forming a wide shallow longitudinal groove on the dorsal face of the hair. The tip is a filament that usually is lacking in aristiforms which are especially strong. Wear probably removes these tips. The aristiforms have the bases whitish or grayish and the amount of pigment gradually increases distally to a dark brown or blackish shade. On the dorsal and lateral surfaces of the head the aristiforms are small and narrow but gradually increase in length and width caudad on the animal. The maximum development is reached in the middorsal region, from where they decrease in size and number toward the lateral surfaces or caudad. This decrease in the development of the aristiforms, however, is not uniformly gradual. Generally, the aristiforms become increasingly conspicuous in a middorsal band, but they extend to the sides and onto the outer sides of the thighs; the band narrows rapidly on the rump. In the subgenus _Trinomys_, where the aristiforms attain their maximum development, they are still strong and conspicuous on the rump and sometimes around the base of the tail. In _Proechimys_ the aristiforms do not extend caudad from the hips. Also, in _Trinomys_, besides the ordinary lanceolate type, there are some aristiforms on the dorsal surface with a clavate shape; the base is wide and the distal part narrow. This parallels the conditions in the pelage of the most spiny species in the genus _Echimys_, _Echimys chrysurus_ (Lichtenstein).

The recently named subspecies _Proechimys cayennensis hoplomyoides_ Tate, 1939, shows an extraordinary development of the aristiforms on the back and sides such as occurs in the genus _Hoplomys_. Actually the small bulla, wide basisphenoid and tooth structure add to the possibility of _hoplomyoides_ being a true _Hoplomys_, and worn teeth might have been responsible for the difficulty which Tate had in allocating the form to the proper genus. However, the narrow braincase is more nearly like that of _Proechimys_ than that of _Hoplomys_. The intermediate nature of _hoplomyoides_ argues for including the genus _Hoplomys_ as a subgenus of _Proechimys_.

Species with narrow aristiforms have a rather soft and flexible pelage, while those with wide aristiforms have harsh, spiny pelage. The aristiforms vary in width from 0.45 to 1.3 mm, depending upon the species or subspecies.

Animals with narrow aristiforms tend to have a more or less uniform coloration throughout the dorsal parts. The blackish distal parts of the aristiforms regularly interline the ground color made by the subapical zone of the setiforms. If, on the contrary, wide aristiforms occur, the dorsal surface is conspicuously marked by the wide blackish lines among spots of color formed by the subapical zones of the setiforms. No clinal variation was detected in width of aristiforms but geographic variation in width was noted; for example, the subspecies of _P. iheringi_ differ in this respect.

The setiforms are narrow and flattened but are without pronouncedly raised margins. The setiforms are usually bicolored on the dorsal and lateral surfaces of the animals, with a subapical zone of some reddish-brown color, like Ochraceous-Orange or Ochraceous-Buff. They are whitish or gray on the basal parts and gradually blacken toward the tip, but have a reddish subapical zone. Common exceptions to this pattern are setiforms without subapical zones; these appear on the dorsal surface among setiforms which are normal in possessing distinctive subapical zones. Also there are setiforms without blackened tips on the lateral surfaces. Due to their relative abundance and subapical color, these setiforms are responsible for the dominant color on the upper parts. Like the aristiforms, they are longer and wider in the middorsal region of the animal and are gradually less developed on the remainder of the upper parts. Actually there is more than one type of setiform in the hair constellation; they vary in length, width and color. Attention was not given, however, to every type of setiform.

The ventral surface of the body and the inner sides of the legs are uniformly covered by short setiforms, thinner and more sparsely distributed on the inner side of the legs. These setiforms are usually uniformly white in color or, sometimes, the distal parts are buff or more richly colored.

Vibrissiforms are scattered on the dorsal and lateral surfaces of the body, and in penicillate arrangements on the head. They are longer than the pelage proper, have a nearly circular cross-section and are blackish in color.

Skull

The absolute size of the skull is proportionate to bulk of the body. The supraorbital and parietal ridges are especially developed in the _P. semispinosus_ group, where they extend across the parietals to the interparietals. In all members of the subgenus _Proechimys_, these ridges extend onto the parietal region. In _Trinomys_, however, they do not extend so far posteriorly as the parietal, but only onto the squamosal.

The rostrum varies from slender to stout. Elongate rostra are common in _Proechimys_; _Trinomys_ has a short blunt rostrum.

The infraorbital foramen commonly has a ventral groove for nerve transmission in many forms of _Proechimys_ but _Trinomys_ almost always lacks this groove. Presence or absence of the groove is a subspecific character in the subgenus _Proechimys_.

The jugals are dorso-ventrally wide in _Trinomys_ except in the species _P. setosus_. In _Proechimys_ a dorso-ventrally narrow jugal is the rule, but _P. canicollis_ has an especially wide jugal. A postorbital process appears on the jugo-squamosal suture and is here called postorbital process of the zygoma. In _Proechimys_ it is more or less weakly developed and shows no variation of systematic worth. In _Trinomys_, on the other hand, this process varies in a clinal way (_P. iheringi_) and stages of the gradient characterize populations of subspecific rank.

Linear and spatulate shape of the humular process of the pterygoid constituted specific characters for Thomas, but there is so much individual variation in the shape of this process in almost every population that it has not been used in the present account.

The mesopterygoid (interpterygoid) fossa in almost every specimen extends anteriorly to the level of M1 or M2 in _Trinomys_, and to M3 in _Proechimys_. Exceptions may occur, as in _P. hendeei_, where the fossa extends to the level of M2.

Incisive Foramen