Our seven specimens are from near the northwestern edge of the geographic range of _orinus_ (where it meets that of _howelli_) as mapped by Hooper (1952:141). Nevertheless, they are distinctly brighter dorsally, paler ventrally, and average larger than the specimens listed in the account of _R. m. howelli_ above. Also, they match well in size and coloration the specimens from nearby Lago de Amatitlan (USNM 275406-09) and Finca San Rafael (CNHM 41770) that were referred by Hooper to _R. m. orinus_. He (_op. cit._:149) noted that these last-mentioned specimens were slightly darker than topotypes of _orinus_ and differed from them in several minor cranial features, which he interpreted as evidence of intergradation with _howelli_. ~_Reithrodontomys brevirostris_~ Goodwin.--COSTA RICA.--Alajuela: 5 mi. SW San Ramón, 1 (KU 71362--July 11, 1956). NICARAGUA.--Carazo: 3 mi. NNW Diriamba, 2 (KU 71390-91--June 16, 21, 1956). External measurements of these three specimens are respectively: total length, 179, 167, 173; length of tail, 107, 96, 101; length of hind foot, 19, 18, 18; length of ear from notch, 15, 13, 13. The teeth show about the same moderate wear in each of the three specimens. Our _brevirostris_ differ noticeably from specimens of _Reithrodontomys mexicanus cherriei_ and _R. m. lucifrons_ that we have seen in duller, darker, and less reddish color. One specimen, KU 71390, still has a patch of gray juvenal pelage on the nape; the newer pelage elsewhere is shorter and sparser than that of the other two specimens. In addition, No. 71390, a female, contained no embryos, but has two pairs of mammae, one pair pectoral and one inguinal, that are conspicuous on the dried skin; perhaps this female was lactating when captured. The mammae of KU 71362, also a non-pregnant female, are inconspicuous on the dried skin. The Nicaraguan specimens extend the known geographic range approximately 270 kilometers northwestward from near Villa Quesada, Alajuela, Costa Rica, and are the first records of the species from Nicaragua. LITERATURE CITED ENGLERT, D. C. 1959. First records of two species of harvest mice in Nicaragua. Southwestern Nat., 4:153, October 24. FELTON, H. 1958. Nagetiere (Mammalia, Rodentia) aus El Salvador, Teil 2. Senckenbergiana Biologica, 39 (1/2):1-10, 1 fig., March 31. HOOPER, E. T. 1952. A systematic review of the harvest mice (genus _Reithrodontomys_) of Latin America. Miscl. Publ. Mus. Zool., Univ. Michigan, 77:1-225, 9 pls., 24 figs., 12 maps, January 16. _Transmitted October 1, 1959._ * * * * * Transcriber's Notes: Bold text is shown within ~tildes~. Italicized text is shown within _underscores_. Bold italicized text is shown within ~_tildes and underscores_~.