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).