Reithrodontomys fulvescens meridionalis, new subspecies
Type specimen.—Skin and skull of adult male, no. 71388 Museum of Natural History, University of Kansas, from 9 mi. NNW Estelí, Estelí, Nicaragua; obtained by J. R. Alcorn on July 15, 1956; original number 21,464.
Diagnostic characters.—A short-tailed Reithrodontomys fulvescens having a distinctly streaked or "peppered," and short pelage composed of relatively dark hairs as well as relatively brightly colored hairs on dorsum and white-tipped hairs on venter; and having shallow skull, elongate and posteriorly attenuate incisive foramina, small postpalatal foramina, broad interorbital region, and mid-dorsal depression at junction of nasal and frontal bones.
Comparisons.—Each of three adults of meridionalis (trapped in February and March) can be distinguished from seven adults of the geographically adjacent R. f. chiapensis from Guatemala (trapped in late January and in March) by shorter tail, more streaked or "peppered" dorsal pelage, yellower hue of non-blackish parts of hairs on dorsum, less distinct mid-dorsal darkening, and more whitish (less buffy) venter.
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).