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.
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 850m altitude (Fazenda Boa 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. 750m), 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 120m 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.
