Part 2

Four specimens of meridionalis trapped in July at the type locality, only one mile from the locality of capture of the February-taken specimens, are distinctly darker dorsally and slightly darker ventrally than the three meridionalis trapped in February and March, but resemble the latter three in shortness of tail and in having short, "peppered" dorsal pelage. We lack specimens of chiapensis in summer pelage. According to Hooper (1952:122) the summer pelages of R. f. chiapensis and R. f. helvolus are indistinguishable. Our meridionalis differ from five summer-taken specimens of helvolus in shorter, more "peppered," and distinctly darker dorsal pelage.

Six skulls of meridionalis were matched with six skulls of chiapensis having approximately the same amount of wear on the teeth, and the series were compared, pair by pair, in various cranial characters. In five of the six pairs meridionalis had a less inflated braincase, and smaller postpalatal foramina, and in each of the six pairs meridionalis had a greater depression in the frontonasal region and posteriorly more acute incisive foramina. Four external measurements and nine cranial measurements were compared using the series of meridionalis, the series of chiapensis from Guatemala, and Hooper's (1952:213) measurements of seven chiapensis from central Chiapas. The lesser average and maximum total length of skull in meridionalis than in either series of chiapensis suggests that meridionalis has a smaller skull. Externally, the lesser total length of meridionalis is largely owing to its shorter tail; there is little difference in length of head and body between meridionalis and chiapensis. The longest tail among our meridionalis is shorter than the shortest tail among the chiapensis (disregarding two Guatemalan specimens of chiapensis that probably had injured tails). The interorbital breadth of meridionalis is on the average greater and the depth of cranium is less than in chiapensis. There is some overlap in the range of each of these two cranial measurements, but in all meridionalis the interorbital breadth exceeds 42 per cent of the depth of cranium, and in all chiapensis is less than 42 per cent. The length of the incisive foramina in meridionalis, expressed as a percentage of the total length of the skull, is usually greater than in chiapensis.

One of our specimens (KU 71389) contained four embryos that measured 5 mm. in crown-rump length.

Measurements.--Selected measurements of the holotype, followed by the average and extreme measurements of six specimens of meridionalis (including the holotype) from the vicinity of the type locality are: total length, 154, 152.0 (148-154); length of tail, 82, 82.0 (81-83); length of hind foot, 17, 18.0 (17-19); length of ear from notch, 13, 13.3 (12-14); total length of skull, 21.4, 21.13 (20.3-21.7); zygomatic breadth, 10.0, 10.38 (10.0-10.6); breadth of braincase, 10.1, 10.17 (9.9-10.4); depth of skull, 8.2, 8.00 (7.8-8.3); interorbital constriction, 3.7, 3.53 (3.4-3.7); breadth of rostrum, 3.8, 3.75 (3.6-3.9); length of rostrum, 7.4, 7.33 (7.1-7.7); length of incisive foramen, 4.6, 4.47 (4.2-4.6); length of upper molar tooth-row, 3.2, 3.32 (3.2-3.5). Corresponding measurements of a specimen from 11 mi. SE Darío are: 153, 82, 18, 13, 20.7, 10.3, 10.1, 7.8, 3.4, 3.6, 7.2, 4.3, and 3.2.

Specimens examined, 8, as follows: NICARAGUA.--Estelí: 9 mi. NNW Estelí, 4 (KU 71386-89--July 15, 1956); 8 mi. NNW Estelí, 3 (KU 71393-95--February 5, 1956). Matagalpa: 11 mi. SE Darío, 1 (KU 71392--March 21, 1956).

Specimens of Reithrodontomys fulvescens helvolus used in comparisons: OAXACA: 3 mi. ESE Oaxaca, 1 (KU 68891--June 24, 1955); 3 mi. W Mitla, 4 (KU 68892-95--August 5 to 9, 1955).

~Reithrodontomys gracilis anthonyi~ Goodwin.--EL SALVADOR.--Santa Ana: 2 mi. SE San Cristóbal, 2950 ft., 2 (KU 65401-02--March 6, 1955). GUATEMALA.--Jutiapa: 2-1/2 mi. W, 2-1/4 mi. N San Cristóbal [El Salvador], 2900 ft., 5 (KU 65396-400--March 6, 1955).

The subspecies anthonyi has been known previously by seven specimens, none of which is fully adult, judging from Hooper's (1952:134) comment that the adult pelage of anthonyi is unknown. Six of our seven specimens are clearly adults as is shown by well-worn teeth and degree of development of temporal ridges. The seventh is a young animal in process of postjuvenal molt. Individuals from our series in general resemble specimens of Reithrodontomys mexicanus orinus from the vicinity of Guatemala City but differ from the latter as follows: dorsal pelage brighter (with less suffusion of black), "peppered" in appearance, shorter and sparser; ears distinctly paler, owing both to the paler color of the skin and the paleness of the hairs inside the pinna; dark tarsal stripe not extending onto hind foot; ears and hind feet uniformly smaller; averaging smaller in cranial dimensions (but there is considerable overlap), braincase less convex dorsally.

Measurements of the adult anthonyi now available show that the subspecies reaches a greater size than was apparent in the sample available to Hooper. Consequently the three largest adults would be identified as R. mexicanus according to Hooper's key (1952:31), rather than R. gracilis, and the three smallest adults could not be unequivocably identified as either one species or the other.

The ranges of R. gracilis and R. mexicanus are allopatric except in southern Guatemala where the ranges overlap. However, the two species have not been taken there at the same place.

In comparison with May-taken adults of R. g. harrisi from 3 mi. SW Managua, Nicaragua, the adult anthonyi average brighter (more orange) in color (but two of the anthonyi cannot be distinguished by color when placed with the harrisi), and are larger in total length, length of tail, and size of skull.

One female (KU 65400) contained two embryos that measured 18 mm. in crown-rump length.

Average and extreme external and cranial measurements of the six adults are: total length, 183.6 (170-198); length of tail, 106.0 (95-113); length of hind foot, 18.0 (18); length of ear from notch, 14.0 (14); total length of skull, 22.21 (21.4-22.8); zygomatic breadth, 11.20 (10.9-11.7); breadth of braincase, 10.90 (10.3-11.4); depth of skull, 8.36 (8.0-9.0); length of rostrum, 7.60 (7.3-7.8); breadth of rostrum, 4.24 (4.0-4.6); interorbital constriction, 3.78 (3.6-4.0); length of incisive foramen, 4.05 (3.8-4.3); length of upper molar tooth-row, 3.28 (3.1-3.4). Weight in grams of the adults averaged 14.3 (12-17).

~Reithrodontomys gracilis gracilis~ Allen and Chapman.--GUATEMALA.--El Petén: Uaxactún, 1500 ft., 2 (KU 65384-85--April 3, 1955).

These specimens are the first of the subspecies to be recorded from Guatemala. Uaxactún is near, but not within, the range of R. g. gracilis as mapped by Hooper (1952:131). The male, KU 65384, and female, KU 65385, are adults with comparatively unworn molar teeth. Respective external measurements are: total length, 178, 175; length of tail, 106, 102; length of hind foot, 18.5, 19; length of ear from notch, 14, 14.

~Reithrodontomys gracilis harrisi~ Goodwin.--NICARAGUA.--Estelí: 9 mi. NNW Estelí, 1 (KU 71342--July 15, 1956). Managua: 3 mi. SW Managua, 15 (KU 71345-59--February, May, June, 1956); 4 mi. W Managua, 2 (KU 71360-61--June 26, 28, 1956).

Comments on the series from 3 mi. SW Managua have appeared elsewhere (Englert, 1959:153). The specimen from 9 mi. NNW Estelí contained four embryos that measured 5 mm. in crown-rump length.

~Reithrodontomys gracilis pacificus~ Goodwin.--EL SALVADOR.--San Salvador: 1 mi. NW San Salvador, 1 (KU 71396--July 29, 1956).

In coloration (being but slightly paler), and in small size, this specimen resembles the description of R. g. pacificus given by Hooper (1952:135) and ten specimens of pacificus (nine from Guatemala and one from Chiapas) examined by us. Because of this resemblance and the marked contrast with specimens of R. g. anthonyi discussed above we assign this specimen to pacificus. In comparison with two topotypes (AMNH 79062, 79090) of R. g. anthonyi from Sacapulas, Guatemala, taken on February 9 and March 2 that are essentially the same age as KU 71396, the latter specimen is darker dorsally, the tail is darker both dorsally and ventrally, and the skull is smaller. In paleness of upper surface of hind feet, length of palate relative to length of incisive foramina, and size of bullae, KU 71396 resembles anthonyi. We interpret these resemblances to anthonyi as evidence of intergradation between pacificus and anthonyi. Felten (1958:9) referred two specimens from El Salvador (one from San Salvador and one from Amate de Campo, Departmento de La Paz) to anthonyi, without comparison with pacificus and with no mention of examination of other specimens of Reithrodontomys gracilis. When the distribution and variation of R. gracilis in this region are more adequately known these two specimens may well be reassigned to pacificus. Hooper (1952:134) observed that two specimens from Monte Cristo Mine in eastern El Salvador were the smallest and darkest of the R. g. anthonyi examined by him and approached R. g. pacificus in these particulars. Possibly these specimens from Monte Cristo Mine also should be assigned to pacificus rather than anthonyi. External measurements of KU 71396 are: total length, 167; length of tail, 99; length of hind foot, 19; length of ear from notch, 13. The specimen contained four embryos that measured 10 mm. in crown-rump length.

~Reithrodontomys microdon microdon~ Merriam.--GUATEMALA.--Huehuetenango: 2 mi. S San Juan Ixcoy, 9340 ft., 10 (KU 65404-13--December 24 and 25, 1954); 3-1/2 mi. SW San Juan Ixcoy, 10,120 ft., 4 (KU 65210, 65414-15, 65417--December 27 and 28, 1954). San Marcos: 3-1/4 mi. N, 3/4 mi. E San Marcos, 9500 ft, 1 (KU 65420--March 22, 1955). Totonicapán: 5 mi. ESE Totonicapán, 4 (KU 68897-900--July 17, 1955).

All the localities from which we have examined specimens fall within the geographic range of the subspecies as mapped by Hooper (1952:168). He examined six specimens of R. m. microdon and listed external and cranial measurements for only two specimens.

Average and extreme external measurements of 13 adults (7 males, 6 females) from the vicinity of San Juan Ixcoy are: total length, 176.5 (168-187); length of tail, 105.8 (100-110); length of hind foot, 19.5 (19-20); length of ear from notch, 16.8 (15-18). The average weight in grams of these same specimens is 9.1 (8-11). Average and extreme cranial measurements of 12 specimens from the same series (7 males, 5 females) are: total length of skull, 22.55 (21.6-23.0); zygomatic breadth, 10.82 (10.2-11.2); breadth of braincase, 11.02 (10.6-11.4); depth of skull, 8.67 (8.4-8.9); interorbital constriction, 3.78 (3.6-3.9); breadth of rostrum, 3.86 (3.6-4.0); length of rostrum, 8.33 (8.1-8.6); length of incisive foramen, 4.27 (4.0-4.5); length of palate, 3.48 (3.2-3.8); length of upper molar tooth-row, 3.25 (3.0-3.4).

~Reithrodontomys mexicanus howelli~ Goodwin.--GUATEMALA.--Baja Verapaz: 5 mi. N, 1 mi. W [Santa Cruz] El Chol, 6000 ft., 3 (KU 65315, 65386-87--January 30, 1955). El Quiche: 1 mi. NE Nebaj, 6000 ft., 2 (KU 65275, 65277--December 19, 1954). Huehuetenango: 5 mi. E, 1 mi. N Huehuetenango, 7000 ft., 2 (KU 65418-19--December 22, 1954). Santa Rosa: 1 mi. WSW El Molino [= approximately 1 mi. S, 6 mi. E Cuajiniquilapa], 1 (KU 71315--August 3, 1956).

The specimen from 1 mi. WSW El Molino is from within the range of the subspecies R. m. orinus as mapped by Hooper (1952:141), coming from a locality to the southeast of the two westernmost localities shown by him for orinus. This mouse is distinctly darker than any of the specimens of orinus discussed beyond, and is as dark as the darkest howelli seen by us. In addition to the specimens of howelli listed above, we have examined 12 from Prusia, Chiapas (UMMZ 88351-58, 96810-13), and three from 3 mi. NW San Cristóbal, Chiapas (KU 66680-82).

R. m. howelli may occur at moderate elevations along the coast of southern Guatemala, or possibly this specimen represents a population of dark-colored mice that is isolated from similarly colored populations to the north and west. According to the field notes of Albert A. Alcorn, the collector, this specimen was taken in a "tree set." Perhaps pale-colored and dark-colored populations of R. mexicanus are sympatric but ecologically segregated in this region.

~Reithrodontomys mexicanus lucifrons~ Howell.--NICARAGUA.--Jinotega: 1 mi. NW Jinotega, 1 (KU 71344--April 12, 1956); 5 mi. S, 2 mi. E Jinotega, 1 (KU 71343--April 12, 1956).

Comments on these specimens have appeared earlier (Englert, 1959:153).

~Reithrodontomys mexicanus orinus~ Hooper.--GUATEMALA.--Guatemala: 5 mi. S Guatemala City, 4950 ft., 2 (KU 65388-89--March 11, 1955); 6 mi. S Guatemala City, 4680 ft., 3 (KU 65390-92--March 10, 1955); 7 mi. S, 6 mi. E Guatemala City, 5800 ft., 2 (KU 65393-94--March 14, 1955).