~_Reithrodontomys sumichrasti australis_~ J. A. Allen.--Seven specimens from the vicinity of Volcan Irazú, Cartago, Costa Rica, are from within the geographic and altitudinal range recorded for the subspecies by Hooper (1952:82). One female, KU 26967, trapped on March 2, 1947, on the SW slope of Volcan Irazú, 8500 ft., contained five embryos that were 17 mm. in crown-rump length. ~_Reithrodontomys sumichrasti dorsalis_~ Merriam.--A total of 93 females are among 195 specimens from 24 localities in Guatemala that lie within the geographic and altitudinal range recorded by Hooper (1952:78) for _dorsalis_. Two females were pregnant; KU 71363, taken on January 28, 1956, 7 mi. E, 2 mi. S La Unión, Quetzaltenango, Guatemala, contained three embryos that were 7 mm. in crown-rump length, and KU 65245, taken on December 15, 1954, 1 mi. NE Nebaj, 6000 ft., El Quiche, Guatemala, contained four embryos that were 15 mm. in crown-rump length. These two females were the only pregnant ones among 36 taken in December, 23 in January, 1 in February, 19 in March, 5 in April, and 9 in August. ~_Reithrodontomys fulvescens chiapensis_~ Howell.--GUATEMALA.--Baja Verapaz: 1/2 mi. N, 1 mi. E Salamá, 3200 ft., 1 (KU 65378--January 28, 1955); 1 mi. S Rabinal, 3450 ft., 4 (KU 65379-82--January 29, 1955); 5 mi. N, 1 mi. W [Santa Cruz] El Chol, 6000 ft., 1 (KU 65375--January 30, 1955). Guatemala: 5 mi. S Guatemala City, 4950 ft., 2 (KU 65371-72--March 13, 1955); 7 mi. S, 6 mi. E Guatemala City, 5800 ft., 1 (KU 65370--March 14, 1955). Santa Rosa: 2 mi. N, 2 mi. W Cuilapa [= Cuajiniquilapa], 2980 ft, 2 (KU 65376-77--March 5, 1955). The specimens from the departments of Guatemala and Santa Rosa are from localities that lie on the Pacific slope and are southwest of the previously known range of the species (see Hooper, 1952:93). The specimens from 1/2 mi. N and 1 mi. E Salamá and from 1 mi. S Rabinal are paler dorsally than other Guatemalan specimens available to us, including the specimen from the nearby locality, 5 mi. N and 1 mi. W El Chol. Specimens from Nicaragua that are recognizable by the E-shaped pattern of the worn occlusal surface of the third upper molars and by the S-shaped occlusal pattern of the third lower molars as of the species _Reithrodontomys fulvescens_, extend the known range of the species approximately 200 kilometers southeast from the vicinity of Tegucigalpa, Honduras (Hooper, 1952:93). The Nicaraguan specimens are described below as a new subspecies. ~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.